/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 */
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <net/netlink.h>
#include <linux/file.h>
#include <linux/vmalloc.h>

/* bpf_check() is a static code analyzer that walks eBPF program
 * instruction by instruction and updates register/stack state.
 * All paths of conditional branches are analyzed until 'bpf_exit' insn.
 *
 * The first pass is depth-first-search to check that the program is a DAG.
 * It rejects the following programs:
 * - larger than BPF_MAXINSNS insns
 * - if loop is present (detected via back-edge)
 * - unreachable insns exist (shouldn't be a forest. program = one function)
 * - out of bounds or malformed jumps
 * The second pass is all possible path descent from the 1st insn.
 * Since it's analyzing all pathes through the program, the length of the
 * analysis is limited to 32k insn, which may be hit even if total number of
 * insn is less then 4K, but there are too many branches that change stack/regs.
 * Number of 'branches to be analyzed' is limited to 1k
 *
 * On entry to each instruction, each register has a type, and the instruction
 * changes the types of the registers depending on instruction semantics.
 * If instruction is BPF_MOV64_REG(BPF_REG_1, BPF_REG_5), then type of R5 is
 * copied to R1.
 *
 * All registers are 64-bit.
 * R0 - return register
 * R1-R5 argument passing registers
 * R6-R9 callee saved registers
 * R10 - frame pointer read-only
 *
 * At the start of BPF program the register R1 contains a pointer to bpf_context
 * and has type PTR_TO_CTX.
 *
 * Verifier tracks arithmetic operations on pointers in case:
 *    BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
 *    BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -20),
 * 1st insn copies R10 (which has FRAME_PTR) type into R1
 * and 2nd arithmetic instruction is pattern matched to recognize
 * that it wants to construct a pointer to some element within stack.
 * So after 2nd insn, the register R1 has type PTR_TO_STACK
 * (and -20 constant is saved for further stack bounds checking).
 * Meaning that this reg is a pointer to stack plus known immediate constant.
 *
 * Most of the time the registers have UNKNOWN_VALUE type, which
 * means the register has some value, but it's not a valid pointer.
 * (like pointer plus pointer becomes UNKNOWN_VALUE type)
 *
 * When verifier sees load or store instructions the type of base register
 * can be: PTR_TO_MAP_VALUE, PTR_TO_CTX, FRAME_PTR. These are three pointer
 * types recognized by check_mem_access() function.
 *
 * PTR_TO_MAP_VALUE means that this register is pointing to 'map element value'
 * and the range of [ptr, ptr + map's value_size) is accessible.
 *
 * registers used to pass values to function calls are checked against
 * function argument constraints.
 *
 * ARG_PTR_TO_MAP_KEY is one of such argument constraints.
 * It means that the register type passed to this function must be
 * PTR_TO_STACK and it will be used inside the function as
 * 'pointer to map element key'
 *
 * For example the argument constraints for bpf_map_lookup_elem():
 *   .ret_type = RET_PTR_TO_MAP_VALUE_OR_NULL,
 *   .arg1_type = ARG_CONST_MAP_PTR,
 *   .arg2_type = ARG_PTR_TO_MAP_KEY,
 *
 * ret_type says that this function returns 'pointer to map elem value or null'
 * function expects 1st argument to be a const pointer to 'struct bpf_map' and
 * 2nd argument should be a pointer to stack, which will be used inside
 * the helper function as a pointer to map element key.
 *
 * On the kernel side the helper function looks like:
 * u64 bpf_map_lookup_elem(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
 * {
 *    struct bpf_map *map = (struct bpf_map *) (unsigned long) r1;
 *    void *key = (void *) (unsigned long) r2;
 *    void *value;
 *
 *    here kernel can access 'key' and 'map' pointers safely, knowing that
 *    [key, key + map->key_size) bytes are valid and were initialized on
 *    the stack of eBPF program.
 * }
 *
 * Corresponding eBPF program may look like:
 *    BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),  // after this insn R2 type is FRAME_PTR
 *    BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), // after this insn R2 type is PTR_TO_STACK
 *    BPF_LD_MAP_FD(BPF_REG_1, map_fd),      // after this insn R1 type is CONST_PTR_TO_MAP
 *    BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
 * here verifier looks at prototype of map_lookup_elem() and sees:
 * .arg1_type == ARG_CONST_MAP_PTR and R1->type == CONST_PTR_TO_MAP, which is ok,
 * Now verifier knows that this map has key of R1->map_ptr->key_size bytes
 *
 * Then .arg2_type == ARG_PTR_TO_MAP_KEY and R2->type == PTR_TO_STACK, ok so far,
 * Now verifier checks that [R2, R2 + map's key_size) are within stack limits
 * and were initialized prior to this call.
 * If it's ok, then verifier allows this BPF_CALL insn and looks at
 * .ret_type which is RET_PTR_TO_MAP_VALUE_OR_NULL, so it sets
 * R0->type = PTR_TO_MAP_VALUE_OR_NULL which means bpf_map_lookup_elem() function
 * returns ether pointer to map value or NULL.
 *
 * When type PTR_TO_MAP_VALUE_OR_NULL passes through 'if (reg != 0) goto +off'
 * insn, the register holding that pointer in the true branch changes state to
 * PTR_TO_MAP_VALUE and the same register changes state to CONST_IMM in the false
 * branch. See check_cond_jmp_op().
 *
 * After the call R0 is set to return type of the function and registers R1-R5
 * are set to NOT_INIT to indicate that they are no longer readable.
 */

/* types of values stored in eBPF registers */
enum bpf_reg_type {
        NOT_INIT = 0,            /* nothing was written into register */
        UNKNOWN_VALUE,           /* reg doesn't contain a valid pointer */
        PTR_TO_CTX,              /* reg points to bpf_context */
        CONST_PTR_TO_MAP,        /* reg points to struct bpf_map */
        PTR_TO_MAP_VALUE,        /* reg points to map element value */
        PTR_TO_MAP_VALUE_OR_NULL,/* points to map elem value or NULL */
        FRAME_PTR,               /* reg == frame_pointer */
        PTR_TO_STACK,            /* reg == frame_pointer + imm */
        CONST_IMM,               /* constant integer value */
};

struct reg_state {
        enum bpf_reg_type type;
        union {
                /* valid when type == CONST_IMM | PTR_TO_STACK */
                int imm;

                /* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
                 *   PTR_TO_MAP_VALUE_OR_NULL
                 */
                struct bpf_map *map_ptr;
        };
};

enum bpf_stack_slot_type {
        STACK_INVALID,    /* nothing was stored in this stack slot */
        STACK_SPILL,      /* register spilled into stack */
        STACK_MISC        /* BPF program wrote some data into this slot */
};

#define BPF_REG_SIZE 8  /* size of eBPF register in bytes */

/* state of the program:
 * type of all registers and stack info
 */
struct verifier_state {
        struct reg_state regs[MAX_BPF_REG];
        u8 stack_slot_type[MAX_BPF_STACK];
        struct reg_state spilled_regs[MAX_BPF_STACK / BPF_REG_SIZE];
};

/* linked list of verifier states used to prune search */
struct verifier_state_list {
        struct verifier_state state;
        struct verifier_state_list *next;
};

/* verifier_state + insn_idx are pushed to stack when branch is encountered */
struct verifier_stack_elem {
        /* verifer state is 'st'
         * before processing instruction 'insn_idx'
         * and after processing instruction 'prev_insn_idx'
         */
        struct verifier_state st;
        int insn_idx;
        int prev_insn_idx;
        struct verifier_stack_elem *next;
};

#define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */

/* single container for all structs
 * one verifier_env per bpf_check() call
 */
struct verifier_env {
        struct bpf_prog *prog;          /* eBPF program being verified */
        struct verifier_stack_elem *head; /* stack of verifier states to be processed */
        int stack_size;                 /* number of states to be processed */
        struct verifier_state cur_state; /* current verifier state */
        struct verifier_state_list **explored_states; /* search pruning optimization */
        struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
        u32 used_map_cnt;               /* number of used maps */
        bool allow_ptr_leaks;
};

/* verbose verifier prints what it's seeing
 * bpf_check() is called under lock, so no race to access these global vars
 */
static u32 log_level, log_size, log_len;
static char *log_buf;

static DEFINE_MUTEX(bpf_verifier_lock);

/* log_level controls verbosity level of eBPF verifier.
 * verbose() is used to dump the verification trace to the log, so the user
 * can figure out what's wrong with the program
 */
static __printf(1, 2) void verbose(const char *fmt, ...)
{
        va_list args;

        if (log_level == 0 || log_len >= log_size - 1)
                return;

        va_start(args, fmt);
        log_len += vscnprintf(log_buf + log_len, log_size - log_len, fmt, args);
        va_end(args);
}

/* string representation of 'enum bpf_reg_type' */
static const char * const reg_type_str[] = {
        [NOT_INIT]              = "?",
        [UNKNOWN_VALUE]         = "inv",
        [PTR_TO_CTX]            = "ctx",
        [CONST_PTR_TO_MAP]      = "map_ptr",
        [PTR_TO_MAP_VALUE]      = "map_value",
        [PTR_TO_MAP_VALUE_OR_NULL] = "map_value_or_null",
        [FRAME_PTR]             = "fp",
        [PTR_TO_STACK]          = "fp",
        [CONST_IMM]             = "imm",
};

static void print_verifier_state(struct verifier_env *env)
{
        enum bpf_reg_type t;
        int i;

        for (i = 0; i < MAX_BPF_REG; i++) {
                t = env->cur_state.regs[i].type;
                if (t == NOT_INIT)
                        continue;
                verbose(" R%d=%s", i, reg_type_str[t]);
                if (t == CONST_IMM || t == PTR_TO_STACK)
                        verbose("%d", env->cur_state.regs[i].imm);
                else if (t == CONST_PTR_TO_MAP || t == PTR_TO_MAP_VALUE ||
                         t == PTR_TO_MAP_VALUE_OR_NULL)
                        verbose("(ks=%d,vs=%d)",
                                env->cur_state.regs[i].map_ptr->key_size,
                                env->cur_state.regs[i].map_ptr->value_size);
        }
        for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) {
                if (env->cur_state.stack_slot_type[i] == STACK_SPILL)
                        verbose(" fp%d=%s", -MAX_BPF_STACK + i,
                                reg_type_str[env->cur_state.spilled_regs[i / BPF_REG_SIZE].type]);
        }
        verbose("\n");
}

static const char *const bpf_class_string[] = {
        [BPF_LD]    = "ld",
        [BPF_LDX]   = "ldx",
        [BPF_ST]    = "st",
        [BPF_STX]   = "stx",
        [BPF_ALU]   = "alu",
        [BPF_JMP]   = "jmp",
        [BPF_RET]   = "BUG",
        [BPF_ALU64] = "alu64",
};

static const char *const bpf_alu_string[16] = {
        [BPF_ADD >> 4]  = "+=",
        [BPF_SUB >> 4]  = "-=",
        [BPF_MUL >> 4]  = "*=",
        [BPF_DIV >> 4]  = "/=",
        [BPF_OR  >> 4]  = "|=",
        [BPF_AND >> 4]  = "&=",
        [BPF_LSH >> 4]  = "<<=",
        [BPF_RSH >> 4]  = ">>=",
        [BPF_NEG >> 4]  = "neg",
        [BPF_MOD >> 4]  = "%=",
        [BPF_XOR >> 4]  = "^=",
        [BPF_MOV >> 4]  = "=",
        [BPF_ARSH >> 4] = "s>>=",
        [BPF_END >> 4]  = "endian",
};

static const char *const bpf_ldst_string[] = {
        [BPF_W >> 3]  = "u32",
        [BPF_H >> 3]  = "u16",
        [BPF_B >> 3]  = "u8",
        [BPF_DW >> 3] = "u64",
};

static const char *const bpf_jmp_string[16] = {
        [BPF_JA >> 4]   = "jmp",
        [BPF_JEQ >> 4]  = "==",
        [BPF_JGT >> 4]  = ">",
        [BPF_JGE >> 4]  = ">=",
        [BPF_JSET >> 4] = "&",
        [BPF_JNE >> 4]  = "!=",
        [BPF_JSGT >> 4] = "s>",
        [BPF_JSGE >> 4] = "s>=",
        [BPF_CALL >> 4] = "call",
        [BPF_EXIT >> 4] = "exit",
};

static void print_bpf_insn(struct bpf_insn *insn)
{
        u8 class = BPF_CLASS(insn->code);

        if (class == BPF_ALU || class == BPF_ALU64) {
                if (BPF_SRC(insn->code) == BPF_X)
                        verbose("(%02x) %sr%d %s %sr%d\n",
                                insn->code, class == BPF_ALU ? "(u32) " : "",
                                insn->dst_reg,
                                bpf_alu_string[BPF_OP(insn->code) >> 4],
                                class == BPF_ALU ? "(u32) " : "",
                                insn->src_reg);
                else
                        verbose("(%02x) %sr%d %s %s%d\n",
                                insn->code, class == BPF_ALU ? "(u32) " : "",
                                insn->dst_reg,
                                bpf_alu_string[BPF_OP(insn->code) >> 4],
                                class == BPF_ALU ? "(u32) " : "",
                                insn->imm);
        } else if (class == BPF_STX) {
                if (BPF_MODE(insn->code) == BPF_MEM)
                        verbose("(%02x) *(%s *)(r%d %+d) = r%d\n",
                                insn->code,
                                bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
                                insn->dst_reg,
                                insn->off, insn->src_reg);
                else if (BPF_MODE(insn->code) == BPF_XADD)
                        verbose("(%02x) lock *(%s *)(r%d %+d) += r%d\n",
                                insn->code,
                                bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
                                insn->dst_reg, insn->off,
                                insn->src_reg);
                else
                        verbose("BUG_%02x\n", insn->code);
        } else if (class == BPF_ST) {
                if (BPF_MODE(insn->code) != BPF_MEM) {
                        verbose("BUG_st_%02x\n", insn->code);
                        return;
                }
                verbose("(%02x) *(%s *)(r%d %+d) = %d\n",
                        insn->code,
                        bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
                        insn->dst_reg,
                        insn->off, insn->imm);
        } else if (class == BPF_LDX) {
                if (BPF_MODE(insn->code) != BPF_MEM) {
                        verbose("BUG_ldx_%02x\n", insn->code);
                        return;
                }
                verbose("(%02x) r%d = *(%s *)(r%d %+d)\n",
                        insn->code, insn->dst_reg,
                        bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
                        insn->src_reg, insn->off);
        } else if (class == BPF_LD) {
                if (BPF_MODE(insn->code) == BPF_ABS) {
                        verbose("(%02x) r0 = *(%s *)skb[%d]\n",
                                insn->code,
                                bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
                                insn->imm);
                } else if (BPF_MODE(insn->code) == BPF_IND) {
                        verbose("(%02x) r0 = *(%s *)skb[r%d + %d]\n",
                                insn->code,
                                bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
                                insn->src_reg, insn->imm);
                } else if (BPF_MODE(insn->code) == BPF_IMM) {
                        verbose("(%02x) r%d = 0x%x\n",
                                insn->code, insn->dst_reg, insn->imm);
                } else {
                        verbose("BUG_ld_%02x\n", insn->code);
                        return;
                }
        } else if (class == BPF_JMP) {
                u8 opcode = BPF_OP(insn->code);

                if (opcode == BPF_CALL) {
                        verbose("(%02x) call %d\n", insn->code, insn->imm);
                } else if (insn->code == (BPF_JMP | BPF_JA)) {
                        verbose("(%02x) goto pc%+d\n",
                                insn->code, insn->off);
                } else if (insn->code == (BPF_JMP | BPF_EXIT)) {
                        verbose("(%02x) exit\n", insn->code);
                } else if (BPF_SRC(insn->code) == BPF_X) {
                        verbose("(%02x) if r%d %s r%d goto pc%+d\n",
                                insn->code, insn->dst_reg,
                                bpf_jmp_string[BPF_OP(insn->code) >> 4],
                                insn->src_reg, insn->off);
                } else {
                        verbose("(%02x) if r%d %s 0x%x goto pc%+d\n",
                                insn->code, insn->dst_reg,
                                bpf_jmp_string[BPF_OP(insn->code) >> 4],
                                insn->imm, insn->off);
                }
        } else {
                verbose("(%02x) %s\n", insn->code, bpf_class_string[class]);
        }
}

static int pop_stack(struct verifier_env *env, int *prev_insn_idx)
{
        struct verifier_stack_elem *elem;
        int insn_idx;

        if (env->head == NULL)
                return -1;

        memcpy(&env->cur_state, &env->head->st, sizeof(env->cur_state));
        insn_idx = env->head->insn_idx;
        if (prev_insn_idx)
                *prev_insn_idx = env->head->prev_insn_idx;
        elem = env->head->next;
        kfree(env->head);
        env->head = elem;
        env->stack_size--;
        return insn_idx;
}

static struct verifier_state *push_stack(struct verifier_env *env, int insn_idx,
                                         int prev_insn_idx)
{
        struct verifier_stack_elem *elem;

        elem = kmalloc(sizeof(struct verifier_stack_elem), GFP_KERNEL);
        if (!elem)
                goto err;

        memcpy(&elem->st, &env->cur_state, sizeof(env->cur_state));
        elem->insn_idx = insn_idx;
        elem->prev_insn_idx = prev_insn_idx;
        elem->next = env->head;
        env->head = elem;
        env->stack_size++;
        if (env->stack_size > 1024) {
                verbose("BPF program is too complex\n");
                goto err;
        }
        return &elem->st;
err:
        /* pop all elements and return */
        while (pop_stack(env, NULL) >= 0);
        return NULL;
}

#define CALLER_SAVED_REGS 6
static const int caller_saved[CALLER_SAVED_REGS] = {
        BPF_REG_0, BPF_REG_1, BPF_REG_2, BPF_REG_3, BPF_REG_4, BPF_REG_5
};

static void init_reg_state(struct reg_state *regs)
{
        int i;

        for (i = 0; i < MAX_BPF_REG; i++) {
                regs[i].type = NOT_INIT;
                regs[i].imm = 0;
                regs[i].map_ptr = NULL;
        }

        /* frame pointer */
        regs[BPF_REG_FP].type = FRAME_PTR;

        /* 1st arg to a function */
        regs[BPF_REG_1].type = PTR_TO_CTX;
}

static void mark_reg_unknown_value(struct reg_state *regs, u32 regno)
{
        BUG_ON(regno >= MAX_BPF_REG);
        regs[regno].type = UNKNOWN_VALUE;
        regs[regno].imm = 0;
        regs[regno].map_ptr = NULL;
}

enum reg_arg_type {
        SRC_OP,         /* register is used as source operand */
        DST_OP,         /* register is used as destination operand */
        DST_OP_NO_MARK  /* same as above, check only, don't mark */
};

static int check_reg_arg(struct reg_state *regs, u32 regno,
                         enum reg_arg_type t)
{
        if (regno >= MAX_BPF_REG) {
                verbose("R%d is invalid\n", regno);
                return -EINVAL;
        }

        if (t == SRC_OP) {
                /* check whether register used as source operand can be read */
                if (regs[regno].type == NOT_INIT) {
                        verbose("R%d !read_ok\n", regno);
                        return -EACCES;
                }
        } else {
                /* check whether register used as dest operand can be written to */
                if (regno == BPF_REG_FP) {
                        verbose("frame pointer is read only\n");
                        return -EACCES;
                }
                if (t == DST_OP)
                        mark_reg_unknown_value(regs, regno);
        }
        return 0;
}

static int bpf_size_to_bytes(int bpf_size)
{
        if (bpf_size == BPF_W)
                return 4;
        else if (bpf_size == BPF_H)
                return 2;
        else if (bpf_size == BPF_B)
                return 1;
        else if (bpf_size == BPF_DW)
                return 8;
        else
                return -EINVAL;
}

static bool is_spillable_regtype(enum bpf_reg_type type)
{
        switch (type) {
        case PTR_TO_MAP_VALUE:
        case PTR_TO_MAP_VALUE_OR_NULL:
        case PTR_TO_STACK:
        case PTR_TO_CTX:
        case FRAME_PTR:
        case CONST_PTR_TO_MAP:
                return true;
        default:
                return false;
        }
}

/* check_stack_read/write functions track spill/fill of registers,
 * stack boundary and alignment are checked in check_mem_access()
 */
static int check_stack_write(struct verifier_state *state, int off, int size,
                             int value_regno)
{
        int i;
        /* caller checked that off % size == 0 and -MAX_BPF_STACK <= off < 0,
         * so it's aligned access and [off, off + size) are within stack limits
         */

        if (value_regno >= 0 &&
            is_spillable_regtype(state->regs[value_regno].type)) {

                /* register containing pointer is being spilled into stack */
                if (size != BPF_REG_SIZE) {
                        verbose("invalid size of register spill\n");
                        return -EACCES;
                }

                /* save register state */
                state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
                        state->regs[value_regno];

                for (i = 0; i < BPF_REG_SIZE; i++)
                        state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_SPILL;
        } else {
                /* regular write of data into stack */
                state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE] =
                        (struct reg_state) {};

                for (i = 0; i < size; i++)
                        state->stack_slot_type[MAX_BPF_STACK + off + i] = STACK_MISC;
        }
        return 0;
}

static int check_stack_read(struct verifier_state *state, int off, int size,
                            int value_regno)
{
        u8 *slot_type;
        int i;

        slot_type = &state->stack_slot_type[MAX_BPF_STACK + off];

        if (slot_type[0] == STACK_SPILL) {
                if (size != BPF_REG_SIZE) {
                        verbose("invalid size of register spill\n");
                        return -EACCES;
                }
                for (i = 1; i < BPF_REG_SIZE; i++) {
                        if (slot_type[i] != STACK_SPILL) {
                                verbose("corrupted spill memory\n");
                                return -EACCES;
                        }
                }

                if (value_regno >= 0)
                        /* restore register state from stack */
                        state->regs[value_regno] =
                                state->spilled_regs[(MAX_BPF_STACK + off) / BPF_REG_SIZE];
                return 0;
        } else {
                for (i = 0; i < size; i++) {
                        if (slot_type[i] != STACK_MISC) {
                                verbose("invalid read from stack off %d+%d size %d\n",
                                        off, i, size);
                                return -EACCES;
                        }
                }
                if (value_regno >= 0)
                        /* have read misc data from the stack */
                        mark_reg_unknown_value(state->regs, value_regno);
                return 0;
        }
}

/* check read/write into map element returned by bpf_map_lookup_elem() */
static int check_map_access(struct verifier_env *env, u32 regno, int off,
                            int size)
{
        struct bpf_map *map = env->cur_state.regs[regno].map_ptr;

        if (off < 0 || off + size > map->value_size) {
                verbose("invalid access to map value, value_size=%d off=%d size=%d\n",
                        map->value_size, off, size);
                return -EACCES;
        }
        return 0;
}

/* check access to 'struct bpf_context' fields */
static int check_ctx_access(struct verifier_env *env, int off, int size,
                            enum bpf_access_type t)
{
        if (env->prog->aux->ops->is_valid_access &&
            env->prog->aux->ops->is_valid_access(off, size, t))
                return 0;

        verbose("invalid bpf_context access off=%d size=%d\n", off, size);
        return -EACCES;
}

static bool is_pointer_value(struct verifier_env *env, int regno)
{
        if (env->allow_ptr_leaks)
                return false;

        switch (env->cur_state.regs[regno].type) {
        case UNKNOWN_VALUE:
        case CONST_IMM:
                return false;
        default:
                return true;
        }
}

/* check whether memory at (regno + off) is accessible for t = (read | write)
 * if t==write, value_regno is a register which value is stored into memory
 * if t==read, value_regno is a register which will receive the value from memory
 * if t==write && value_regno==-1, some unknown value is stored into memory
 * if t==read && value_regno==-1, don't care what we read from memory
 */
static int check_mem_access(struct verifier_env *env, u32 regno, int off,
                            int bpf_size, enum bpf_access_type t,
                            int value_regno)
{
        struct verifier_state *state = &env->cur_state;
        int size, err = 0;

        if (state->regs[regno].type == PTR_TO_STACK)
                off += state->regs[regno].imm;

        size = bpf_size_to_bytes(bpf_size);
        if (size < 0)
                return size;

        if (off % size != 0) {
                verbose("misaligned access off %d size %d\n", off, size);
                return -EACCES;
        }

        if (state->regs[regno].type == PTR_TO_MAP_VALUE) {
                if (t == BPF_WRITE && value_regno >= 0 &&
                    is_pointer_value(env, value_regno)) {
                        verbose("R%d leaks addr into map\n", value_regno);
                        return -EACCES;
                }
                err = check_map_access(env, regno, off, size);
                if (!err && t == BPF_READ && value_regno >= 0)
                        mark_reg_unknown_value(state->regs, value_regno);

        } else if (state->regs[regno].type == PTR_TO_CTX) {
                if (t == BPF_WRITE && value_regno >= 0 &&
                    is_pointer_value(env, value_regno)) {
                        verbose("R%d leaks addr into ctx\n", value_regno);
                        return -EACCES;
                }
                err = check_ctx_access(env, off, size, t);
                if (!err && t == BPF_READ && value_regno >= 0)
                        mark_reg_unknown_value(state->regs, value_regno);

        } else if (state->regs[regno].type == FRAME_PTR ||
                   state->regs[regno].type == PTR_TO_STACK) {
                if (off >= 0 || off < -MAX_BPF_STACK) {
                        verbose("invalid stack off=%d size=%d\n", off, size);
                        return -EACCES;
                }
                if (t == BPF_WRITE) {
                        if (!env->allow_ptr_leaks &&
                            state->stack_slot_type[MAX_BPF_STACK + off] == STACK_SPILL &&
                            size != BPF_REG_SIZE) {
                                verbose("attempt to corrupt spilled pointer on stack\n");
                                return -EACCES;
                        }
                        err = check_stack_write(state, off, size, value_regno);
                } else {
                        err = check_stack_read(state, off, size, value_regno);
                }
        } else {
                verbose("R%d invalid mem access '%s'\n",
                        regno, reg_type_str[state->regs[regno].type]);
                return -EACCES;
        }
        return err;
}

static int check_xadd(struct verifier_env *env, struct bpf_insn *insn)
{
        struct reg_state *regs = env->cur_state.regs;
        int err;

        if ((BPF_SIZE(insn->code) != BPF_W && BPF_SIZE(insn->code) != BPF_DW) ||
            insn->imm != 0) {
                verbose("BPF_XADD uses reserved fields\n");
                return -EINVAL;
        }

        /* check src1 operand */
        err = check_reg_arg(regs, insn->src_reg, SRC_OP);
        if (err)
                return err;

        /* check src2 operand */
        err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
        if (err)
                return err;

        /* check whether atomic_add can read the memory */
        err = check_mem_access(env, insn->dst_reg, insn->off,
                               BPF_SIZE(insn->code), BPF_READ, -1);
        if (err)
                return err;

        /* check whether atomic_add can write into the same memory */
        return check_mem_access(env, insn->dst_reg, insn->off,
                                BPF_SIZE(insn->code), BPF_WRITE, -1);
}

/* when register 'regno' is passed into function that will read 'access_size'
 * bytes from that pointer, make sure that it's within stack boundary
 * and all elements of stack are initialized
 */
static int check_stack_boundary(struct verifier_env *env, int regno,
                                int access_size, bool zero_size_allowed)
{
        struct verifier_state *state = &env->cur_state;
        struct reg_state *regs = state->regs;
        int off, i;

        if (regs[regno].type != PTR_TO_STACK) {
                if (zero_size_allowed && access_size == 0 &&
                    regs[regno].type == CONST_IMM &&
                    regs[regno].imm  == 0)
                        return 0;

                verbose("R%d type=%s expected=%s\n", regno,
                        reg_type_str[regs[regno].type],
                        reg_type_str[PTR_TO_STACK]);
                return -EACCES;
        }

        off = regs[regno].imm;
        if (off >= 0 || off < -MAX_BPF_STACK || off + access_size > 0 ||
            access_size <= 0) {
                verbose("invalid stack type R%d off=%d access_size=%d\n",
                        regno, off, access_size);
                return -EACCES;
        }

        for (i = 0; i < access_size; i++) {
                if (state->stack_slot_type[MAX_BPF_STACK + off + i] != STACK_MISC) {
                        verbose("invalid indirect read from stack off %d+%d size %d\n",
                                off, i, access_size);
                        return -EACCES;
                }
        }
        return 0;
}

static int check_func_arg(struct verifier_env *env, u32 regno,
                          enum bpf_arg_type arg_type, struct bpf_map **mapp)
{
        struct reg_state *reg = env->cur_state.regs + regno;
        enum bpf_reg_type expected_type;
        int err = 0;

        if (arg_type == ARG_DONTCARE)
                return 0;

        if (reg->type == NOT_INIT) {
                verbose("R%d !read_ok\n", regno);
                return -EACCES;
        }

        if (arg_type == ARG_ANYTHING) {
                if (is_pointer_value(env, regno)) {
                        verbose("R%d leaks addr into helper function\n", regno);
                        return -EACCES;
                }
                return 0;
        }

        if (arg_type == ARG_PTR_TO_MAP_KEY ||
            arg_type == ARG_PTR_TO_MAP_VALUE) {
                expected_type = PTR_TO_STACK;
        } else if (arg_type == ARG_CONST_STACK_SIZE ||
                   arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
                expected_type = CONST_IMM;
        } else if (arg_type == ARG_CONST_MAP_PTR) {
                expected_type = CONST_PTR_TO_MAP;
        } else if (arg_type == ARG_PTR_TO_CTX) {
                expected_type = PTR_TO_CTX;
        } else if (arg_type == ARG_PTR_TO_STACK) {
                expected_type = PTR_TO_STACK;
                /* One exception here. In case function allows for NULL to be
                 * passed in as argument, it's a CONST_IMM type. Final test
                 * happens during stack boundary checking.
                 */
                if (reg->type == CONST_IMM && reg->imm == 0)
                        expected_type = CONST_IMM;
        } else {
                verbose("unsupported arg_type %d\n", arg_type);
                return -EFAULT;
        }

        if (reg->type != expected_type) {
                verbose("R%d type=%s expected=%s\n", regno,
                        reg_type_str[reg->type], reg_type_str[expected_type]);
                return -EACCES;
        }

        if (arg_type == ARG_CONST_MAP_PTR) {
                /* bpf_map_xxx(map_ptr) call: remember that map_ptr */
                *mapp = reg->map_ptr;

        } else if (arg_type == ARG_PTR_TO_MAP_KEY) {
                /* bpf_map_xxx(..., map_ptr, ..., key) call:
                 * check that [key, key + map->key_size) are within
                 * stack limits and initialized
                 */
                if (!*mapp) {
                        /* in function declaration map_ptr must come before
                         * map_key, so that it's verified and known before
                         * we have to check map_key here. Otherwise it means
                         * that kernel subsystem misconfigured verifier
                         */
                        verbose("invalid map_ptr to access map->key\n");
                        return -EACCES;
                }
                err = check_stack_boundary(env, regno, (*mapp)->key_size,
                                           false);
        } else if (arg_type == ARG_PTR_TO_MAP_VALUE) {
                /* bpf_map_xxx(..., map_ptr, ..., value) call:
                 * check [value, value + map->value_size) validity
                 */
                if (!*mapp) {
                        /* kernel subsystem misconfigured verifier */
                        verbose("invalid map_ptr to access map->value\n");
                        return -EACCES;
                }
                err = check_stack_boundary(env, regno, (*mapp)->value_size,
                                           false);
        } else if (arg_type == ARG_CONST_STACK_SIZE ||
                   arg_type == ARG_CONST_STACK_SIZE_OR_ZERO) {
                bool zero_size_allowed = (arg_type == ARG_CONST_STACK_SIZE_OR_ZERO);

                /* bpf_xxx(..., buf, len) call will access 'len' bytes
                 * from stack pointer 'buf'. Check it
                 * note: regno == len, regno - 1 == buf
                 */
                if (regno == 0) {
                        /* kernel subsystem misconfigured verifier */
                        verbose("ARG_CONST_STACK_SIZE cannot be first argument\n");
                        return -EACCES;
                }
                err = check_stack_boundary(env, regno - 1, reg->imm,
                                           zero_size_allowed);
        }

        return err;
}

static int check_map_func_compatibility(struct bpf_map *map, int func_id)
{
        if (!map)
                return 0;

        /* We need a two way check, first is from map perspective ... */
        switch (map->map_type) {
        case BPF_MAP_TYPE_PROG_ARRAY:
                if (func_id != BPF_FUNC_tail_call)
                        goto error;
                break;
        case BPF_MAP_TYPE_PERF_EVENT_ARRAY:
                if (func_id != BPF_FUNC_perf_event_read &&
                    func_id != BPF_FUNC_perf_event_output)
                        goto error;
                break;
        case BPF_MAP_TYPE_STACK_TRACE:
                if (func_id != BPF_FUNC_get_stackid)
                        goto error;
                break;
        default:
                break;
        }

        /* ... and second from the function itself. */
        switch (func_id) {
        case BPF_FUNC_tail_call:
                if (map->map_type != BPF_MAP_TYPE_PROG_ARRAY)
                        goto error;
                break;
        case BPF_FUNC_perf_event_read:
        case BPF_FUNC_perf_event_output:
                if (map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
                        goto error;
                break;
        case BPF_FUNC_get_stackid:
                if (map->map_type != BPF_MAP_TYPE_STACK_TRACE)
                        goto error;
                break;
        default:
                break;
        }

        return 0;
error:
        verbose("cannot pass map_type %d into func %d\n",
                map->map_type, func_id);
        return -EINVAL;
}

static int check_call(struct verifier_env *env, int func_id)
{
        struct verifier_state *state = &env->cur_state;
        const struct bpf_func_proto *fn = NULL;
        struct reg_state *regs = state->regs;
        struct bpf_map *map = NULL;
        struct reg_state *reg;
        int i, err;

        /* find function prototype */
        if (func_id < 0 || func_id >= __BPF_FUNC_MAX_ID) {
                verbose("invalid func %d\n", func_id);
                return -EINVAL;
        }

        if (env->prog->aux->ops->get_func_proto)
                fn = env->prog->aux->ops->get_func_proto(func_id);

        if (!fn) {
                verbose("unknown func %d\n", func_id);
                return -EINVAL;
        }

        /* eBPF programs must be GPL compatible to use GPL-ed functions */
        if (!env->prog->gpl_compatible && fn->gpl_only) {
                verbose("cannot call GPL only function from proprietary program\n");
                return -EINVAL;
        }

        /* check args */
        err = check_func_arg(env, BPF_REG_1, fn->arg1_type, &map);
        if (err)
                return err;
        err = check_func_arg(env, BPF_REG_2, fn->arg2_type, &map);
        if (err)
                return err;
        err = check_func_arg(env, BPF_REG_3, fn->arg3_type, &map);
        if (err)
                return err;

        err = check_func_arg(env, BPF_REG_4, fn->arg4_type, &map);
        if (err)
                return err;
        err = check_func_arg(env, BPF_REG_5, fn->arg5_type, &map);
        if (err)
                return err;

        /* reset caller saved regs */
        for (i = 0; i < CALLER_SAVED_REGS; i++) {
                reg = regs + caller_saved[i];
                reg->type = NOT_INIT;
                reg->imm = 0;
        }

        /* update return register */
        if (fn->ret_type == RET_INTEGER) {
                regs[BPF_REG_0].type = UNKNOWN_VALUE;
        } else if (fn->ret_type == RET_VOID) {
                regs[BPF_REG_0].type = NOT_INIT;
        } else if (fn->ret_type == RET_PTR_TO_MAP_VALUE_OR_NULL) {
                regs[BPF_REG_0].type = PTR_TO_MAP_VALUE_OR_NULL;
                /* remember map_ptr, so that check_map_access()
                 * can check 'value_size' boundary of memory access
                 * to map element returned from bpf_map_lookup_elem()
                 */
                if (map == NULL) {
                        verbose("kernel subsystem misconfigured verifier\n");
                        return -EINVAL;
                }
                regs[BPF_REG_0].map_ptr = map;
        } else {
                verbose("unknown return type %d of func %d\n",
                        fn->ret_type, func_id);
                return -EINVAL;
        }

        err = check_map_func_compatibility(map, func_id);
        if (err)
                return err;

        return 0;
}

/* check validity of 32-bit and 64-bit arithmetic operations */
static int check_alu_op(struct verifier_env *env, struct bpf_insn *insn)
{
        struct reg_state *regs = env->cur_state.regs;
        u8 opcode = BPF_OP(insn->code);
        int err;

        if (opcode == BPF_END || opcode == BPF_NEG) {
                if (opcode == BPF_NEG) {
                        if (BPF_SRC(insn->code) != 0 ||
                            insn->src_reg != BPF_REG_0 ||
                            insn->off != 0 || insn->imm != 0) {
                                verbose("BPF_NEG uses reserved fields\n");
                                return -EINVAL;
                        }
                } else {
                        if (insn->src_reg != BPF_REG_0 || insn->off != 0 ||
                            (insn->imm != 16 && insn->imm != 32 && insn->imm != 64)) {
                                verbose("BPF_END uses reserved fields\n");
                                return -EINVAL;
                        }
                }

                /* check src operand */
                err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
                if (err)
                        return err;

                if (is_pointer_value(env, insn->dst_reg)) {
                        verbose("R%d pointer arithmetic prohibited\n",
                                insn->dst_reg);
                        return -EACCES;
                }

                /* check dest operand */
                err = check_reg_arg(regs, insn->dst_reg, DST_OP);
                if (err)
                        return err;

        } else if (opcode == BPF_MOV) {

                if (BPF_SRC(insn->code) == BPF_X) {
                        if (insn->imm != 0 || insn->off != 0) {
                                verbose("BPF_MOV uses reserved fields\n");
                                return -EINVAL;
                        }

                        /* check src operand */
                        err = check_reg_arg(regs, insn->src_reg, SRC_OP);
                        if (err)
                                return err;
                } else {
                        if (insn->src_reg != BPF_REG_0 || insn->off != 0) {
                                verbose("BPF_MOV uses reserved fields\n");
                                return -EINVAL;
                        }
                }

                /* check dest operand */
                err = check_reg_arg(regs, insn->dst_reg, DST_OP);
                if (err)
                        return err;

                if (BPF_SRC(insn->code) == BPF_X) {
                        if (BPF_CLASS(insn->code) == BPF_ALU64) {
                                /* case: R1 = R2
                                 * copy register state to dest reg
                                 */
                                regs[insn->dst_reg] = regs[insn->src_reg];
                        } else {
                                if (is_pointer_value(env, insn->src_reg)) {
                                        verbose("R%d partial copy of pointer\n",
                                                insn->src_reg);
                                        return -EACCES;
                                }
                                regs[insn->dst_reg].type = UNKNOWN_VALUE;
                                regs[insn->dst_reg].map_ptr = NULL;
                        }
                } else {
                        /* case: R = imm
                         * remember the value we stored into this reg
                         */
                        regs[insn->dst_reg].type = CONST_IMM;
                        regs[insn->dst_reg].imm = insn->imm;
                }

        } else if (opcode > BPF_END) {
                verbose("invalid BPF_ALU opcode %x\n", opcode);
                return -EINVAL;

        } else {        /* all other ALU ops: and, sub, xor, add, ... */

                bool stack_relative = false;

                if (BPF_SRC(insn->code) == BPF_X) {
                        if (insn->imm != 0 || insn->off != 0) {
                                verbose("BPF_ALU uses reserved fields\n");
                                return -EINVAL;
                        }
                        /* check src1 operand */
                        err = check_reg_arg(regs, insn->src_reg, SRC_OP);
                        if (err)
                                return err;
                } else {
                        if (insn->src_reg != BPF_REG_0 || insn->off != 0) {
                                verbose("BPF_ALU uses reserved fields\n");
                                return -EINVAL;
                        }
                }

                /* check src2 operand */
                err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
                if (err)
                        return err;

                if ((opcode == BPF_MOD || opcode == BPF_DIV) &&
                    BPF_SRC(insn->code) == BPF_K && insn->imm == 0) {
                        verbose("div by zero\n");
                        return -EINVAL;
                }

                if ((opcode == BPF_LSH || opcode == BPF_RSH ||
                     opcode == BPF_ARSH) && BPF_SRC(insn->code) == BPF_K) {
                        int size = BPF_CLASS(insn->code) == BPF_ALU64 ? 64 : 32;

                        if (insn->imm < 0 || insn->imm >= size) {
                                verbose("invalid shift %d\n", insn->imm);
                                return -EINVAL;
                        }
                }

                /* pattern match 'bpf_add Rx, imm' instruction */
                if (opcode == BPF_ADD && BPF_CLASS(insn->code) == BPF_ALU64 &&
                    regs[insn->dst_reg].type == FRAME_PTR &&
                    BPF_SRC(insn->code) == BPF_K) {
                        stack_relative = true;
                } else if (is_pointer_value(env, insn->dst_reg)) {
                        verbose("R%d pointer arithmetic prohibited\n",
                                insn->dst_reg);
                        return -EACCES;
                } else if (BPF_SRC(insn->code) == BPF_X &&
                           is_pointer_value(env, insn->src_reg)) {
                        verbose("R%d pointer arithmetic prohibited\n",
                                insn->src_reg);
                        return -EACCES;
                }

                /* check dest operand */
                err = check_reg_arg(regs, insn->dst_reg, DST_OP);
                if (err)
                        return err;

                if (stack_relative) {
                        regs[insn->dst_reg].type = PTR_TO_STACK;
                        regs[insn->dst_reg].imm = insn->imm;
                }
        }

        return 0;
}

static int check_cond_jmp_op(struct verifier_env *env,
                             struct bpf_insn *insn, int *insn_idx)
{
        struct reg_state *regs = env->cur_state.regs;
        struct verifier_state *other_branch;
        u8 opcode = BPF_OP(insn->code);
        int err;

        if (opcode > BPF_EXIT) {
                verbose("invalid BPF_JMP opcode %x\n", opcode);
                return -EINVAL;
        }

        if (BPF_SRC(insn->code) == BPF_X) {
                if (insn->imm != 0) {
                        verbose("BPF_JMP uses reserved fields\n");
                        return -EINVAL;
                }

                /* check src1 operand */
                err = check_reg_arg(regs, insn->src_reg, SRC_OP);
                if (err)
                        return err;

                if (is_pointer_value(env, insn->src_reg)) {
                        verbose("R%d pointer comparison prohibited\n",
                                insn->src_reg);
                        return -EACCES;
                }
        } else {
                if (insn->src_reg != BPF_REG_0) {
                        verbose("BPF_JMP uses reserved fields\n");
                        return -EINVAL;
                }
        }

        /* check src2 operand */
        err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
        if (err)
                return err;

        /* detect if R == 0 where R was initialized to zero earlier */
        if (BPF_SRC(insn->code) == BPF_K &&
            (opcode == BPF_JEQ || opcode == BPF_JNE) &&
            regs[insn->dst_reg].type == CONST_IMM &&
            regs[insn->dst_reg].imm == insn->imm) {
                if (opcode == BPF_JEQ) {
                        /* if (imm == imm) goto pc+off;
                         * only follow the goto, ignore fall-through
                         */
                        *insn_idx += insn->off;
                        return 0;
                } else {
                        /* if (imm != imm) goto pc+off;
                         * only follow fall-through branch, since
                         * that's where the program will go
                         */
                        return 0;
                }
        }

        other_branch = push_stack(env, *insn_idx + insn->off + 1, *insn_idx);
        if (!other_branch)
                return -EFAULT;

        /* detect if R == 0 where R is returned value from bpf_map_lookup_elem() */
        if (BPF_SRC(insn->code) == BPF_K &&
            insn->imm == 0 && (opcode == BPF_JEQ ||
                               opcode == BPF_JNE) &&
            regs[insn->dst_reg].type == PTR_TO_MAP_VALUE_OR_NULL) {
                if (opcode == BPF_JEQ) {
                        /* next fallthrough insn can access memory via
                         * this register
                         */
                        regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
                        /* branch targer cannot access it, since reg == 0 */
                        other_branch->regs[insn->dst_reg].type = CONST_IMM;
                        other_branch->regs[insn->dst_reg].imm = 0;
                } else {
                        other_branch->regs[insn->dst_reg].type = PTR_TO_MAP_VALUE;
                        regs[insn->dst_reg].type = CONST_IMM;
                        regs[insn->dst_reg].imm = 0;
                }
        } else if (is_pointer_value(env, insn->dst_reg)) {
                verbose("R%d pointer comparison prohibited\n", insn->dst_reg);
                return -EACCES;
        } else if (BPF_SRC(insn->code) == BPF_K &&
                   (opcode == BPF_JEQ || opcode == BPF_JNE)) {

                if (opcode == BPF_JEQ) {
                        /* detect if (R == imm) goto
                         * and in the target state recognize that R = imm
                         */
                        other_branch->regs[insn->dst_reg].type = CONST_IMM;
                        other_branch->regs[insn->dst_reg].imm = insn->imm;
                } else {
                        /* detect if (R != imm) goto
                         * and in the fall-through state recognize that R = imm
                         */
                        regs[insn->dst_reg].type = CONST_IMM;
                        regs[insn->dst_reg].imm = insn->imm;
                }
        }
        if (log_level)
                print_verifier_state(env);
        return 0;
}

/* return the map pointer stored inside BPF_LD_IMM64 instruction */
static struct bpf_map *ld_imm64_to_map_ptr(struct bpf_insn *insn)
{
        u64 imm64 = ((u64) (u32) insn[0].imm) | ((u64) (u32) insn[1].imm) << 32;

        return (struct bpf_map *) (unsigned long) imm64;
}

/* verify BPF_LD_IMM64 instruction */
static int check_ld_imm(struct verifier_env *env, struct bpf_insn *insn)
{
        struct reg_state *regs = env->cur_state.regs;
        int err;

        if (BPF_SIZE(insn->code) != BPF_DW) {
                verbose("invalid BPF_LD_IMM insn\n");
                return -EINVAL;
        }
        if (insn->off != 0) {
                verbose("BPF_LD_IMM64 uses reserved fields\n");
                return -EINVAL;
        }

        err = check_reg_arg(regs, insn->dst_reg, DST_OP);
        if (err)
                return err;

        if (insn->src_reg == 0)
                /* generic move 64-bit immediate into a register */
                return 0;

        /* replace_map_fd_with_map_ptr() should have caught bad ld_imm64 */
        BUG_ON(insn->src_reg != BPF_PSEUDO_MAP_FD);

        regs[insn->dst_reg].type = CONST_PTR_TO_MAP;
        regs[insn->dst_reg].map_ptr = ld_imm64_to_map_ptr(insn);
        return 0;
}

static bool may_access_skb(enum bpf_prog_type type)
{
        switch (type) {
        case BPF_PROG_TYPE_SOCKET_FILTER:
        case BPF_PROG_TYPE_SCHED_CLS:
        case BPF_PROG_TYPE_SCHED_ACT:
                return true;
        default:
                return false;
        }
}

/* verify safety of LD_ABS|LD_IND instructions:
 * - they can only appear in the programs where ctx == skb
 * - since they are wrappers of function calls, they scratch R1-R5 registers,
 *   preserve R6-R9, and store return value into R0
 *
 * Implicit input:
 *   ctx == skb == R6 == CTX
 *
 * Explicit input:
 *   SRC == any register
 *   IMM == 32-bit immediate
 *
 * Output:
 *   R0 - 8/16/32-bit skb data converted to cpu endianness
 */
static int check_ld_abs(struct verifier_env *env, struct bpf_insn *insn)
{
        struct reg_state *regs = env->cur_state.regs;
        u8 mode = BPF_MODE(insn->code);
        struct reg_state *reg;
        int i, err;

        if (!may_access_skb(env->prog->type)) {
                verbose("BPF_LD_ABS|IND instructions not allowed for this program type\n");
                return -EINVAL;
        }

        if (insn->dst_reg != BPF_REG_0 || insn->off != 0 ||
            BPF_SIZE(insn->code) == BPF_DW ||
            (mode == BPF_ABS && insn->src_reg != BPF_REG_0)) {
                verbose("BPF_LD_ABS uses reserved fields\n");
                return -EINVAL;
        }

        /* check whether implicit source operand (register R6) is readable */
        err = check_reg_arg(regs, BPF_REG_6, SRC_OP);
        if (err)
                return err;

        if (regs[BPF_REG_6].type != PTR_TO_CTX) {
                verbose("at the time of BPF_LD_ABS|IND R6 != pointer to skb\n");
                return -EINVAL;
        }

        if (mode == BPF_IND) {
                /* check explicit source operand */
                err = check_reg_arg(regs, insn->src_reg, SRC_OP);
                if (err)
                        return err;
        }

        /* reset caller saved regs to unreadable */
        for (i = 0; i < CALLER_SAVED_REGS; i++) {
                reg = regs + caller_saved[i];
                reg->type = NOT_INIT;
                reg->imm = 0;
        }

        /* mark destination R0 register as readable, since it contains
         * the value fetched from the packet
         */
        regs[BPF_REG_0].type = UNKNOWN_VALUE;
        return 0;
}

/* non-recursive DFS pseudo code
 * 1  procedure DFS-iterative(G,v):
 * 2      label v as discovered
 * 3      let S be a stack
 * 4      S.push(v)
 * 5      while S is not empty
 * 6            t <- S.pop()
 * 7            if t is what we're looking for:
 * 8                return t
 * 9            for all edges e in G.adjacentEdges(t) do
 * 10               if edge e is already labelled
 * 11                   continue with the next edge
 * 12               w <- G.adjacentVertex(t,e)
 * 13               if vertex w is not discovered and not explored
 * 14                   label e as tree-edge
 * 15                   label w as discovered
 * 16                   S.push(w)
 * 17                   continue at 5
 * 18               else if vertex w is discovered
 * 19                   label e as back-edge
 * 20               else
 * 21                   // vertex w is explored
 * 22                   label e as forward- or cross-edge
 * 23           label t as explored
 * 24           S.pop()
 *
 * convention:
 * 0x10 - discovered
 * 0x11 - discovered and fall-through edge labelled
 * 0x12 - discovered and fall-through and branch edges labelled
 * 0x20 - explored
 */

enum {
        DISCOVERED = 0x10,
        EXPLORED = 0x20,
        FALLTHROUGH = 1,
        BRANCH = 2,
};

#define STATE_LIST_MARK ((struct verifier_state_list *) -1L)

static int *insn_stack; /* stack of insns to process */
static int cur_stack;   /* current stack index */
static int *insn_state;

/* t, w, e - match pseudo-code above:
 * t - index of current instruction
 * w - next instruction
 * e - edge
 */
static int push_insn(int t, int w, int e, struct verifier_env *env)
{
        if (e == FALLTHROUGH && insn_state[t] >= (DISCOVERED | FALLTHROUGH))
                return 0;

        if (e == BRANCH && insn_state[t] >= (DISCOVERED | BRANCH))
                return 0;

        if (w < 0 || w >= env->prog->len) {
                verbose("jump out of range from insn %d to %d\n", t, w);
                return -EINVAL;
        }

        if (e == BRANCH)
                /* mark branch target for state pruning */
                env->explored_states[w] = STATE_LIST_MARK;

        if (insn_state[w] == 0) {
                /* tree-edge */
                insn_state[t] = DISCOVERED | e;
                insn_state[w] = DISCOVERED;
                if (cur_stack >= env->prog->len)
                        return -E2BIG;
                insn_stack[cur_stack++] = w;
                return 1;
        } else if ((insn_state[w] & 0xF0) == DISCOVERED) {
                verbose("back-edge from insn %d to %d\n", t, w);
                return -EINVAL;
        } else if (insn_state[w] == EXPLORED) {
                /* forward- or cross-edge */
                insn_state[t] = DISCOVERED | e;
        } else {
                verbose("insn state internal bug\n");
                return -EFAULT;
        }
        return 0;
}

/* non-recursive depth-first-search to detect loops in BPF program
 * loop == back-edge in directed graph
 */
static int check_cfg(struct verifier_env *env)
{
        struct bpf_insn *insns = env->prog->insnsi;
        int insn_cnt = env->prog->len;
        int ret = 0;
        int i, t;

        insn_state = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
        if (!insn_state)
                return -ENOMEM;

        insn_stack = kcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
        if (!insn_stack) {
                kfree(insn_state);
                return -ENOMEM;
        }

        insn_state[0] = DISCOVERED; /* mark 1st insn as discovered */
        insn_stack[0] = 0; /* 0 is the first instruction */
        cur_stack = 1;

peek_stack:
        if (cur_stack == 0)
                goto check_state;
        t = insn_stack[cur_stack - 1];

        if (BPF_CLASS(insns[t].code) == BPF_JMP) {
                u8 opcode = BPF_OP(insns[t].code);

                if (opcode == BPF_EXIT) {
                        goto mark_explored;
                } else if (opcode == BPF_CALL) {
                        ret = push_insn(t, t + 1, FALLTHROUGH, env);
                        if (ret == 1)
                                goto peek_stack;
                        else if (ret < 0)
                                goto err_free;
                } else if (opcode == BPF_JA) {
                        if (BPF_SRC(insns[t].code) != BPF_K) {
                                ret = -EINVAL;
                                goto err_free;
                        }
                        /* unconditional jump with single edge */
                        ret = push_insn(t, t + insns[t].off + 1,
                                        FALLTHROUGH, env);
                        if (ret == 1)
                                goto peek_stack;
                        else if (ret < 0)
                                goto err_free;
                        /* tell verifier to check for equivalent states
                         * after every call and jump
                         */
                        if (t + 1 < insn_cnt)
                                env->explored_states[t + 1] = STATE_LIST_MARK;
                } else {
                        /* conditional jump with two edges */
                        ret = push_insn(t, t + 1, FALLTHROUGH, env);
                        if (ret == 1)
                                goto peek_stack;
                        else if (ret < 0)
                                goto err_free;

                        ret = push_insn(t, t + insns[t].off + 1, BRANCH, env);
                        if (ret == 1)
                                goto peek_stack;
                        else if (ret < 0)
                                goto err_free;
                }
        } else {
                /* all other non-branch instructions with single
                 * fall-through edge
                 */
                ret = push_insn(t, t + 1, FALLTHROUGH, env);
                if (ret == 1)
                        goto peek_stack;
                else if (ret < 0)
                        goto err_free;
        }

mark_explored:
        insn_state[t] = EXPLORED;
        if (cur_stack-- <= 0) {
                verbose("pop stack internal bug\n");
                ret = -EFAULT;
                goto err_free;
        }
        goto peek_stack;

check_state:
        for (i = 0; i < insn_cnt; i++) {
                if (insn_state[i] != EXPLORED) {
                        verbose("unreachable insn %d\n", i);
                        ret = -EINVAL;
                        goto err_free;
                }
        }
        ret = 0; /* cfg looks good */

err_free:
        kfree(insn_state);
        kfree(insn_stack);
        return ret;
}

/* compare two verifier states
 *
 * all states stored in state_list are known to be valid, since
 * verifier reached 'bpf_exit' instruction through them
 *
 * this function is called when verifier exploring different branches of
 * execution popped from the state stack. If it sees an old state that has
 * more strict register state and more strict stack state then this execution
 * branch doesn't need to be explored further, since verifier already
 * concluded that more strict state leads to valid finish.
 *
 * Therefore two states are equivalent if register state is more conservative
 * and explored stack state is more conservative than the current one.
 * Example:
 *       explored                   current
 * (slot1=INV slot2=MISC) == (slot1=MISC slot2=MISC)
 * (slot1=MISC slot2=MISC) != (slot1=INV slot2=MISC)
 *
 * In other words if current stack state (one being explored) has more
 * valid slots than old one that already passed validation, it means
 * the verifier can stop exploring and conclude that current state is valid too
 *
 * Similarly with registers. If explored state has register type as invalid
 * whereas register type in current state is meaningful, it means that
 * the current state will reach 'bpf_exit' instruction safely
 */
static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
{
        int i;

        for (i = 0; i < MAX_BPF_REG; i++) {
                if (memcmp(&old->regs[i], &cur->regs[i],
                           sizeof(old->regs[0])) != 0) {
                        if (old->regs[i].type == NOT_INIT ||
                            (old->regs[i].type == UNKNOWN_VALUE &&
                             cur->regs[i].type != NOT_INIT))
                                continue;
                        return false;
                }
        }

        for (i = 0; i < MAX_BPF_STACK; i++) {
                if (old->stack_slot_type[i] == STACK_INVALID)
                        continue;
                if (old->stack_slot_type[i] != cur->stack_slot_type[i])
                        /* Ex: old explored (safe) state has STACK_SPILL in
                         * this stack slot, but current has has STACK_MISC ->
                         * this verifier states are not equivalent,
                         * return false to continue verification of this path
                         */
                        return false;
                if (i % BPF_REG_SIZE)
                        continue;
                if (memcmp(&old->spilled_regs[i / BPF_REG_SIZE],
                           &cur->spilled_regs[i / BPF_REG_SIZE],
                           sizeof(old->spilled_regs[0])))
                        /* when explored and current stack slot types are
                         * the same, check that stored pointers types
                         * are the same as well.
                         * Ex: explored safe path could have stored
                         * (struct reg_state) {.type = PTR_TO_STACK, .imm = -8}
                         * but current path has stored:
                         * (struct reg_state) {.type = PTR_TO_STACK, .imm = -16}
                         * such verifier states are not equivalent.
                         * return false to continue verification of this path
                         */
                        return false;
                else
                        continue;
        }
        return true;
}

static int is_state_visited(struct verifier_env *env, int insn_idx)
{
        struct verifier_state_list *new_sl;
        struct verifier_state_list *sl;

        sl = env->explored_states[insn_idx];
        if (!sl)
                /* this 'insn_idx' instruction wasn't marked, so we will not
                 * be doing state search here
                 */
                return 0;

        while (sl != STATE_LIST_MARK) {
                if (states_equal(&sl->state, &env->cur_state))
                        /* reached equivalent register/stack state,
                         * prune the search
                         */
                        return 1;
                sl = sl->next;
        }

        /* there were no equivalent states, remember current one.
         * technically the current state is not proven to be safe yet,
         * but it will either reach bpf_exit (which means it's safe) or
         * it will be rejected. Since there are no loops, we won't be
         * seeing this 'insn_idx' instruction again on the way to bpf_exit
         */
        new_sl = kmalloc(sizeof(struct verifier_state_list), GFP_USER);
        if (!new_sl)
                return -ENOMEM;

        /* add new state to the head of linked list */
        memcpy(&new_sl->state, &env->cur_state, sizeof(env->cur_state));
        new_sl->next = env->explored_states[insn_idx];
        env->explored_states[insn_idx] = new_sl;
        return 0;
}

static int do_check(struct verifier_env *env)
{
        struct verifier_state *state = &env->cur_state;
        struct bpf_insn *insns = env->prog->insnsi;
        struct reg_state *regs = state->regs;
        int insn_cnt = env->prog->len;
        int insn_idx, prev_insn_idx = 0;
        int insn_processed = 0;
        bool do_print_state = false;

        init_reg_state(regs);
        insn_idx = 0;
        for (;;) {
                struct bpf_insn *insn;
                u8 class;
                int err;

                if (insn_idx >= insn_cnt) {
                        verbose("invalid insn idx %d insn_cnt %d\n",
                                insn_idx, insn_cnt);
                        return -EFAULT;
                }

                insn = &insns[insn_idx];
                class = BPF_CLASS(insn->code);

                if (++insn_processed > 32768) {
                        verbose("BPF program is too large. Proccessed %d insn\n",
                                insn_processed);
                        return -E2BIG;
                }

                err = is_state_visited(env, insn_idx);
                if (err < 0)
                        return err;
                if (err == 1) {
                        /* found equivalent state, can prune the search */
                        if (log_level) {
                                if (do_print_state)
                                        verbose("\nfrom %d to %d: safe\n",
                                                prev_insn_idx, insn_idx);
                                else
                                        verbose("%d: safe\n", insn_idx);
                        }
                        goto process_bpf_exit;
                }

                if (log_level && do_print_state) {
                        verbose("\nfrom %d to %d:", prev_insn_idx, insn_idx);
                        print_verifier_state(env);
                        do_print_state = false;
                }

                if (log_level) {
                        verbose("%d: ", insn_idx);
                        print_bpf_insn(insn);
                }

                if (class == BPF_ALU || class == BPF_ALU64) {
                        err = check_alu_op(env, insn);
                        if (err)
                                return err;

                } else if (class == BPF_LDX) {
                        enum bpf_reg_type src_reg_type;

                        /* check for reserved fields is already done */

                        /* check src operand */
                        err = check_reg_arg(regs, insn->src_reg, SRC_OP);
                        if (err)
                                return err;

                        err = check_reg_arg(regs, insn->dst_reg, DST_OP_NO_MARK);
                        if (err)
                                return err;

                        src_reg_type = regs[insn->src_reg].type;

                        /* check that memory (src_reg + off) is readable,
                         * the state of dst_reg will be updated by this func
                         */
                        err = check_mem_access(env, insn->src_reg, insn->off,
                                               BPF_SIZE(insn->code), BPF_READ,
                                               insn->dst_reg);
                        if (err)
                                return err;

                        if (BPF_SIZE(insn->code) != BPF_W) {
                                insn_idx++;
                                continue;
                        }

                        if (insn->imm == 0) {
                                /* saw a valid insn
                                 * dst_reg = *(u32 *)(src_reg + off)
                                 * use reserved 'imm' field to mark this insn
                                 */
                                insn->imm = src_reg_type;

                        } else if (src_reg_type != insn->imm &&
                                   (src_reg_type == PTR_TO_CTX ||
                                    insn->imm == PTR_TO_CTX)) {
                                /* ABuser program is trying to use the same insn
                                 * dst_reg = *(u32*) (src_reg + off)
                                 * with different pointer types:
                                 * src_reg == ctx in one branch and
                                 * src_reg == stack|map in some other branch.
                                 * Reject it.
                                 */
                                verbose("same insn cannot be used with different pointers\n");
                                return -EINVAL;
                        }

                } else if (class == BPF_STX) {
                        enum bpf_reg_type dst_reg_type;

                        if (BPF_MODE(insn->code) == BPF_XADD) {
                                err = check_xadd(env, insn);
                                if (err)
                                        return err;
                                insn_idx++;
                                continue;
                        }

                        /* check src1 operand */
                        err = check_reg_arg(regs, insn->src_reg, SRC_OP);
                        if (err)
                                return err;
                        /* check src2 operand */
                        err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
                        if (err)
                                return err;

                        dst_reg_type = regs[insn->dst_reg].type;

                        /* check that memory (dst_reg + off) is writeable */
                        err = check_mem_access(env, insn->dst_reg, insn->off,
                                               BPF_SIZE(insn->code), BPF_WRITE,
                                               insn->src_reg);
                        if (err)
                                return err;

                        if (insn->imm == 0) {
                                insn->imm = dst_reg_type;
                        } else if (dst_reg_type != insn->imm &&
                                   (dst_reg_type == PTR_TO_CTX ||
                                    insn->imm == PTR_TO_CTX)) {
                                verbose("same insn cannot be used with different pointers\n");
                                return -EINVAL;
                        }

                } else if (class == BPF_ST) {
                        if (BPF_MODE(insn->code) != BPF_MEM ||
                            insn->src_reg != BPF_REG_0) {
                                verbose("BPF_ST uses reserved fields\n");
                                return -EINVAL;
                        }
                        /* check src operand */
                        err = check_reg_arg(regs, insn->dst_reg, SRC_OP);
                        if (err)
                                return err;

                        /* check that memory (dst_reg + off) is writeable */
                        err = check_mem_access(env, insn->dst_reg, insn->off,
                                               BPF_SIZE(insn->code), BPF_WRITE,
                                               -1);
                        if (err)
                                return err;

                } else if (class == BPF_JMP) {
                        u8 opcode = BPF_OP(insn->code);

                        if (opcode == BPF_CALL) {
                                if (BPF_SRC(insn->code) != BPF_K ||
                                    insn->off != 0 ||
                                    insn->src_reg != BPF_REG_0 ||
                                    insn->dst_reg != BPF_REG_0) {
                                        verbose("BPF_CALL uses reserved fields\n");
                                        return -EINVAL;
                                }

                                err = check_call(env, insn->imm);
                                if (err)
                                        return err;

                        } else if (opcode == BPF_JA) {
                                if (BPF_SRC(insn->code) != BPF_K ||
                                    insn->imm != 0 ||
                                    insn->src_reg != BPF_REG_0 ||
                                    insn->dst_reg != BPF_REG_0) {
                                        verbose("BPF_JA uses reserved fields\n");
                                        return -EINVAL;
                                }

                                insn_idx += insn->off + 1;
                                continue;

                        } else if (opcode == BPF_EXIT) {
                                if (BPF_SRC(insn->code) != BPF_K ||
                                    insn->imm != 0 ||
                                    insn->src_reg != BPF_REG_0 ||
                                    insn->dst_reg != BPF_REG_0) {
                                        verbose("BPF_EXIT uses reserved fields\n");
                                        return -EINVAL;
                                }

                                /* eBPF calling convetion is such that R0 is used
                                 * to return the value from eBPF program.
                                 * Make sure that it's readable at this time
                                 * of bpf_exit, which means that program wrote
                                 * something into it earlier
                                 */
                                err = check_reg_arg(regs, BPF_REG_0, SRC_OP);
                                if (err)
                                        return err;

                                if (is_pointer_value(env, BPF_REG_0)) {
                                        verbose("R0 leaks addr as return value\n");
                                        return -EACCES;
                                }

process_bpf_exit:
                                insn_idx = pop_stack(env, &prev_insn_idx);
                                if (insn_idx < 0) {
                                        break;
                                } else {
                                        do_print_state = true;
                                        continue;
                                }
                        } else {
                                err = check_cond_jmp_op(env, insn, &insn_idx);
                                if (err)
                                        return err;
                        }
                } else if (class == BPF_LD) {
                        u8 mode = BPF_MODE(insn->code);

                        if (mode == BPF_ABS || mode == BPF_IND) {
                                err = check_ld_abs(env, insn);
                                if (err)
                                        return err;

                        } else if (mode == BPF_IMM) {
                                err = check_ld_imm(env, insn);
                                if (err)
                                        return err;

                                insn_idx++;
                        } else {
                                verbose("invalid BPF_LD mode\n");
                                return -EINVAL;
                        }
                } else {
                        verbose("unknown insn class %d\n", class);
                        return -EINVAL;
                }

                insn_idx++;
        }

        return 0;
}

/* look for pseudo eBPF instructions that access map FDs and

 * replace them with actual map pointers
 */
static int replace_map_fd_with_map_ptr(struct verifier_env *env)
{
        struct bpf_insn *insn = env->prog->insnsi;
        int insn_cnt = env->prog->len;
        int i, j;

        for (i = 0; i < insn_cnt; i++, insn++) {
                if (BPF_CLASS(insn->code) == BPF_LDX &&
                    (BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
                        verbose("BPF_LDX uses reserved fields\n");
                        return -EINVAL;
                }

                if (BPF_CLASS(insn->code) == BPF_STX &&
                    ((BPF_MODE(insn->code) != BPF_MEM &&
                      BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
                        verbose("BPF_STX uses reserved fields\n");
                        return -EINVAL;
                }

                if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
                        struct bpf_map *map;
                        struct fd f;

                        if (i == insn_cnt - 1 || insn[1].code != 0 ||
                            insn[1].dst_reg != 0 || insn[1].src_reg != 0 ||
                            insn[1].off != 0) {
                                verbose("invalid bpf_ld_imm64 insn\n");
                                return -EINVAL;
                        }

                        if (insn->src_reg == 0)
                                /* valid generic load 64-bit imm */
                                goto next_insn;

                        if (insn->src_reg != BPF_PSEUDO_MAP_FD) {
                                verbose("unrecognized bpf_ld_imm64 insn\n");
                                return -EINVAL;
                        }

                        f = fdget(insn->imm);
                        map = __bpf_map_get(f);
                        if (IS_ERR(map)) {
                                verbose("fd %d is not pointing to valid bpf_map\n",
                                        insn->imm);
                                return PTR_ERR(map);
                        }

                        /* store map pointer inside BPF_LD_IMM64 instruction */
                        insn[0].imm = (u32) (unsigned long) map;
                        insn[1].imm = ((u64) (unsigned long) map) >> 32;

                        /* check whether we recorded this map already */
                        for (j = 0; j < env->used_map_cnt; j++)
                                if (env->used_maps[j] == map) {
                                        fdput(f);
                                        goto next_insn;
                                }

                        if (env->used_map_cnt >= MAX_USED_MAPS) {
                                fdput(f);
                                return -E2BIG;
                        }

                        /* hold the map. If the program is rejected by verifier,
                         * the map will be released by release_maps() or it
                         * will be used by the valid program until it's unloaded
                         * and all maps are released in free_bpf_prog_info()
                         */
                        map = bpf_map_inc(map, false);
                        if (IS_ERR(map)) {
                                fdput(f);
                                return PTR_ERR(map);
                        }
                        env->used_maps[env->used_map_cnt++] = map;

                        fdput(f);
next_insn:
                        insn++;
                        i++;
                }
        }

        /* now all pseudo BPF_LD_IMM64 instructions load valid
         * 'struct bpf_map *' into a register instead of user map_fd.
         * These pointers will be used later by verifier to validate map access.
         */
        return 0;
}

/* drop refcnt of maps used by the rejected program */
static void release_maps(struct verifier_env *env)
{
        int i;

        for (i = 0; i < env->used_map_cnt; i++)
                bpf_map_put(env->used_maps[i]);
}

/* convert pseudo BPF_LD_IMM64 into generic BPF_LD_IMM64 */
static void convert_pseudo_ld_imm64(struct verifier_env *env)
{
        struct bpf_insn *insn = env->prog->insnsi;
        int insn_cnt = env->prog->len;
        int i;

        for (i = 0; i < insn_cnt; i++, insn++)
                if (insn->code == (BPF_LD | BPF_IMM | BPF_DW))
                        insn->src_reg = 0;
}

static void adjust_branches(struct bpf_prog *prog, int pos, int delta)
{
        struct bpf_insn *insn = prog->insnsi;
        int insn_cnt = prog->len;
        int i;

        for (i = 0; i < insn_cnt; i++, insn++) {
                if (BPF_CLASS(insn->code) != BPF_JMP ||
                    BPF_OP(insn->code) == BPF_CALL ||
                    BPF_OP(insn->code) == BPF_EXIT)
                        continue;

                /* adjust offset of jmps if necessary */
                if (i < pos && i + insn->off + 1 > pos)
                        insn->off += delta;
                else if (i > pos + delta && i + insn->off + 1 <= pos + delta)
                        insn->off -= delta;
        }
}

/* convert load instructions that access fields of 'struct __sk_buff'
 * into sequence of instructions that access fields of 'struct sk_buff'
 */
static int convert_ctx_accesses(struct verifier_env *env)
{
        struct bpf_insn *insn = env->prog->insnsi;
        int insn_cnt = env->prog->len;
        struct bpf_insn insn_buf[16];
        struct bpf_prog *new_prog;
        u32 cnt;
        int i;
        enum bpf_access_type type;

        if (!env->prog->aux->ops->convert_ctx_access)
                return 0;

        for (i = 0; i < insn_cnt; i++, insn++) {
                if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
                        type = BPF_READ;
                else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
                        type = BPF_WRITE;
                else
                        continue;

                if (insn->imm != PTR_TO_CTX) {
                        /* clear internal mark */
                        insn->imm = 0;
                        continue;
                }

                cnt = env->prog->aux->ops->
                        convert_ctx_access(type, insn->dst_reg, insn->src_reg,
                                           insn->off, insn_buf, env->prog);
                if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
                        verbose("bpf verifier is misconfigured\n");
                        return -EINVAL;
                }

                if (cnt == 1) {
                        memcpy(insn, insn_buf, sizeof(*insn));
                        continue;
                }

                /* several new insns need to be inserted. Make room for them */
                insn_cnt += cnt - 1;
                new_prog = bpf_prog_realloc(env->prog,
                                            bpf_prog_size(insn_cnt),
                                            GFP_USER);
                if (!new_prog)
                        return -ENOMEM;

                new_prog->len = insn_cnt;

                memmove(new_prog->insnsi + i + cnt, new_prog->insns + i + 1,
                        sizeof(*insn) * (insn_cnt - i - cnt));

                /* copy substitute insns in place of load instruction */
                memcpy(new_prog->insnsi + i, insn_buf, sizeof(*insn) * cnt);

                /* adjust branches in the whole program */
                adjust_branches(new_prog, i, cnt - 1);

                /* keep walking new program and skip insns we just inserted */
                env->prog = new_prog;
                insn = new_prog->insnsi + i + cnt - 1;
                i += cnt - 1;
        }

        return 0;
}

static void free_states(struct verifier_env *env)
{
        struct verifier_state_list *sl, *sln;
        int i;

        if (!env->explored_states)
                return;

        for (i = 0; i < env->prog->len; i++) {
                sl = env->explored_states[i];

                if (sl)
                        while (sl != STATE_LIST_MARK) {
                                sln = sl->next;
                                kfree(sl);
                                sl = sln;
                        }
        }

        kfree(env->explored_states);
}

int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
{
        char __user *log_ubuf = NULL;
        struct verifier_env *env;
        int ret = -EINVAL;

        if ((*prog)->len <= 0 || (*prog)->len > BPF_MAXINSNS)
                return -E2BIG;

        /* 'struct verifier_env' can be global, but since it's not small,
         * allocate/free it every time bpf_check() is called
         */
        env = kzalloc(sizeof(struct verifier_env), GFP_KERNEL);
        if (!env)
                return -ENOMEM;

        env->prog = *prog;

        /* grab the mutex to protect few globals used by verifier */
        mutex_lock(&bpf_verifier_lock);

        if (attr->log_level || attr->log_buf || attr->log_size) {
                /* user requested verbose verifier output
                 * and supplied buffer to store the verification trace
                 */
                log_level = attr->log_level;
                log_ubuf = (char __user *) (unsigned long) attr->log_buf;
                log_size = attr->log_size;
                log_len = 0;

                ret = -EINVAL;
                /* log_* values have to be sane */
                if (log_size < 128 || log_size > UINT_MAX >> 8 ||
                    log_level == 0 || log_ubuf == NULL)
                        goto free_env;

                ret = -ENOMEM;
                log_buf = vmalloc(log_size);
                if (!log_buf)
                        goto free_env;
        } else {
                log_level = 0;
        }

        ret = replace_map_fd_with_map_ptr(env);
        if (ret < 0)
                goto skip_full_check;

        env->explored_states = kcalloc(env->prog->len,
                                       sizeof(struct verifier_state_list *),
                                       GFP_USER);
        ret = -ENOMEM;
        if (!env->explored_states)
                goto skip_full_check;

        ret = check_cfg(env);
        if (ret < 0)
                goto skip_full_check;

        env->allow_ptr_leaks = capable(CAP_SYS_ADMIN);

        ret = do_check(env);

skip_full_check:
        while (pop_stack(env, NULL) >= 0);
        free_states(env);

        if (ret == 0)
                /* program is valid, convert *(u32*)(ctx + off) accesses */
                ret = convert_ctx_accesses(env);

        if (log_level && log_len >= log_size - 1) {
                BUG_ON(log_len >= log_size);
                /* verifier log exceeded user supplied buffer */
                ret = -ENOSPC;
                /* fall through to return what was recorded */
        }

        /* copy verifier log back to user space including trailing zero */
        if (log_level && copy_to_user(log_ubuf, log_buf, log_len + 1) != 0) {
                ret = -EFAULT;
                goto free_log_buf;
        }

        if (ret == 0 && env->used_map_cnt) {
                /* if program passed verifier, update used_maps in bpf_prog_info */
                env->prog->aux->used_maps = kmalloc_array(env->used_map_cnt,
                                                          sizeof(env->used_maps[0]),
                                                          GFP_KERNEL);

                if (!env->prog->aux->used_maps) {
                        ret = -ENOMEM;
                        goto free_log_buf;
                }

                memcpy(env->prog->aux->used_maps, env->used_maps,
                       sizeof(env->used_maps[0]) * env->used_map_cnt);
                env->prog->aux->used_map_cnt = env->used_map_cnt;

                /* program is valid. Convert pseudo bpf_ld_imm64 into generic
                 * bpf_ld_imm64 instructions
                 */
                convert_pseudo_ld_imm64(env);
        }

free_log_buf:
        if (log_level)
                vfree(log_buf);
free_env:
        if (!env->prog->aux->used_maps)
                /* if we didn't copy map pointers into bpf_prog_info, release
                 * them now. Otherwise free_bpf_prog_info() will release them.
                 */
                release_maps(env);
        *prog = env->prog;
        kfree(env);
        mutex_unlock(&bpf_verifier_lock);
        return ret;
}