// SPDX-License-Identifier: GPL-2.0
/*
 * This is for all the tests related to logic bugs (e.g. bad dereferences,
 * bad alignment, bad loops, bad locking, bad scheduling, deep stacks, and
 * lockups) along with other things that don't fit well into existing LKDTM
 * test source files.
 */
#include "lkdtm.h"
#include <linux/list.h>
#include <linux/sched.h>
#include <linux/sched/signal.h>
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>

struct lkdtm_list {
        struct list_head node;
};

/*
 * Make sure our attempts to over run the kernel stack doesn't trigger
 * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we
 * recurse past the end of THREAD_SIZE by default.
 */
#if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0)
#define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2)
#else
#define REC_STACK_SIZE (THREAD_SIZE / 8)
#endif
#define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2)

static int recur_count = REC_NUM_DEFAULT;

static DEFINE_SPINLOCK(lock_me_up);

/*
 * Make sure compiler does not optimize this function or stack frame away:
 * - function marked noinline
 * - stack variables are marked volatile
 * - stack variables are written (memset()) and read (pr_info())
 * - function has external effects (pr_info())
 * */
static int noinline recursive_loop(int remaining)
{
        volatile char buf[REC_STACK_SIZE];

        memset((void *)buf, remaining & 0xFF, sizeof(buf));
        pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)],
                recur_count);
        if (!remaining)
                return 0;
        else
                return recursive_loop(remaining - 1);
}

/* If the depth is negative, use the default, otherwise keep parameter. */
void __init lkdtm_bugs_init(int *recur_param)
{
        if (*recur_param < 0)
                *recur_param = recur_count;
        else
                recur_count = *recur_param;
}

void lkdtm_PANIC(void)
{
        panic("dumptest");
}

void lkdtm_BUG(void)
{
        BUG();
}

static int warn_counter;

void lkdtm_WARNING(void)
{
        WARN(1, "Warning message trigger count: %d\n", warn_counter++);
}

void lkdtm_EXCEPTION(void)
{
        *((volatile int *) 0) = 0;
}

void lkdtm_LOOP(void)
{
        for (;;)
                ;
}

void lkdtm_EXHAUST_STACK(void)
{
        pr_info("Calling function with %lu frame size to depth %d ...\n",
                REC_STACK_SIZE, recur_count);
        recursive_loop(recur_count);
        pr_info("FAIL: survived without exhausting stack?!\n");
}

static noinline void __lkdtm_CORRUPT_STACK(void *stack)
{
        memset(stack, '\xff', 64);
}

/* This should trip the stack canary, not corrupt the return address. */
noinline void lkdtm_CORRUPT_STACK(void)
{
        /* Use default char array length that triggers stack protection. */
        char data[8] __aligned(sizeof(void *));

        __lkdtm_CORRUPT_STACK(&data);

        pr_info("Corrupted stack containing char array ...\n");
}

/* Same as above but will only get a canary with -fstack-protector-strong */
noinline void lkdtm_CORRUPT_STACK_STRONG(void)
{
        union {
                unsigned short shorts[4];
                unsigned long *ptr;
        } data __aligned(sizeof(void *));

        __lkdtm_CORRUPT_STACK(&data);

        pr_info("Corrupted stack containing union ...\n");
}

void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
{
        static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
        u32 *p;
        u32 val = 0x12345678;

        p = (u32 *)(data + 1);
        if (*p == 0)
                val = 0x87654321;
        *p = val;
}

void lkdtm_SOFTLOCKUP(void)
{
        preempt_disable();
        for (;;)
                cpu_relax();
}

void lkdtm_HARDLOCKUP(void)
{
        local_irq_disable();
        for (;;)
                cpu_relax();
}

void lkdtm_SPINLOCKUP(void)
{
        /* Must be called twice to trigger. */
        spin_lock(&lock_me_up);
        /* Let sparse know we intended to exit holding the lock. */
        __release(&lock_me_up);
}

void lkdtm_HUNG_TASK(void)
{
        set_current_state(TASK_UNINTERRUPTIBLE);
        schedule();
}

void lkdtm_CORRUPT_LIST_ADD(void)
{
        /*
         * Initially, an empty list via LIST_HEAD:
         *      test_head.next = &test_head
         *      test_head.prev = &test_head
         */
        LIST_HEAD(test_head);
        struct lkdtm_list good, bad;
        void *target[2] = { };
        void *redirection = &target;

        pr_info("attempting good list addition\n");

        /*
         * Adding to the list performs these actions:
         *      test_head.next->prev = &good.node
         *      good.node.next = test_head.next
         *      good.node.prev = test_head
         *      test_head.next = good.node
         */
        list_add(&good.node, &test_head);

        pr_info("attempting corrupted list addition\n");
        /*
         * In simulating this "write what where" primitive, the "what" is
         * the address of &bad.node, and the "where" is the address held
         * by "redirection".
         */
        test_head.next = redirection;
        list_add(&bad.node, &test_head);

        if (target[0] == NULL && target[1] == NULL)
                pr_err("Overwrite did not happen, but no BUG?!\n");
        else
                pr_err("list_add() corruption not detected!\n");
}

void lkdtm_CORRUPT_LIST_DEL(void)
{
        LIST_HEAD(test_head);
        struct lkdtm_list item;
        void *target[2] = { };
        void *redirection = &target;

        list_add(&item.node, &test_head);

        pr_info("attempting good list removal\n");
        list_del(&item.node);

        pr_info("attempting corrupted list removal\n");
        list_add(&item.node, &test_head);

        /* As with the list_add() test above, this corrupts "next". */
        item.node.next = redirection;
        list_del(&item.node);

        if (target[0] == NULL && target[1] == NULL)
                pr_err("Overwrite did not happen, but no BUG?!\n");
        else
                pr_err("list_del() corruption not detected!\n");
}

/* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */
void lkdtm_CORRUPT_USER_DS(void)
{
        pr_info("setting bad task size limit\n");
        set_fs(KERNEL_DS);

        /* Make sure we do not keep running with a KERNEL_DS! */
        force_sig(SIGKILL);
}

/* Test that VMAP_STACK is actually allocating with a leading guard page */
void lkdtm_STACK_GUARD_PAGE_LEADING(void)
{
        const unsigned char *stack = task_stack_page(current);
        const unsigned char *ptr = stack - 1;
        volatile unsigned char byte;

        pr_info("attempting bad read from page below current stack\n");

        byte = *ptr;

        pr_err("FAIL: accessed page before stack!\n");
}

/* Test that VMAP_STACK is actually allocating with a trailing guard page */
void lkdtm_STACK_GUARD_PAGE_TRAILING(void)
{
        const unsigned char *stack = task_stack_page(current);
        const unsigned char *ptr = stack + THREAD_SIZE;
        volatile unsigned char byte;

        pr_info("attempting bad read from page above current stack\n");

        byte = *ptr;

        pr_err("FAIL: accessed page after stack!\n");
}

void lkdtm_UNSET_SMEP(void)
{
#ifdef CONFIG_X86_64
#define MOV_CR4_DEPTH   64
        void (*direct_write_cr4)(unsigned long val);
        unsigned char *insn;
        unsigned long cr4;
        int i;

        cr4 = native_read_cr4();

        if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) {
                pr_err("FAIL: SMEP not in use\n");
                return;
        }
        cr4 &= ~(X86_CR4_SMEP);

        pr_info("trying to clear SMEP normally\n");
        native_write_cr4(cr4);
        if (cr4 == native_read_cr4()) {
                pr_err("FAIL: pinning SMEP failed!\n");
                cr4 |= X86_CR4_SMEP;
                pr_info("restoring SMEP\n");
                native_write_cr4(cr4);
                return;
        }
        pr_info("ok: SMEP did not get cleared\n");

        /*
         * To test the post-write pinning verification we need to call
         * directly into the middle of native_write_cr4() where the
         * cr4 write happens, skipping any pinning. This searches for
         * the cr4 writing instruction.
         */
        insn = (unsigned char *)native_write_cr4;
        for (i = 0; i < MOV_CR4_DEPTH; i++) {
                /* mov %rdi, %cr4 */
                if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7)
                        break;
                /* mov %rdi,%rax; mov %rax, %cr4 */
                if (insn[i]   == 0x48 && insn[i+1] == 0x89 &&
                    insn[i+2] == 0xf8 && insn[i+3] == 0x0f &&
                    insn[i+4] == 0x22 && insn[i+5] == 0xe0)
                        break;
        }
        if (i >= MOV_CR4_DEPTH) {
                pr_info("ok: cannot locate cr4 writing call gadget\n");
                return;
        }
        direct_write_cr4 = (void *)(insn + i);

        pr_info("trying to clear SMEP with call gadget\n");
        direct_write_cr4(cr4);
        if (native_read_cr4() & X86_CR4_SMEP) {
                pr_info("ok: SMEP removal was reverted\n");
        } else {
                pr_err("FAIL: cleared SMEP not detected!\n");
                cr4 |= X86_CR4_SMEP;
                pr_info("restoring SMEP\n");
                native_write_cr4(cr4);
        }
#else
        pr_err("FAIL: this test is x86_64-only\n");
#endif
}