// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2019 Facebook */

#include <linux/bpf.h>
#include <linux/bpf_verifier.h>
#include <linux/btf.h>
#include <linux/filter.h>
#include <linux/slab.h>
#include <linux/numa.h>
#include <linux/seq_file.h>
#include <linux/refcount.h>
#include <linux/mutex.h>

enum bpf_struct_ops_state {
        BPF_STRUCT_OPS_STATE_INIT,
        BPF_STRUCT_OPS_STATE_INUSE,
        BPF_STRUCT_OPS_STATE_TOBEFREE,
};

#define BPF_STRUCT_OPS_COMMON_VALUE                     \
        refcount_t refcnt;                              \
        enum bpf_struct_ops_state state

struct bpf_struct_ops_value {
        BPF_STRUCT_OPS_COMMON_VALUE;
        char data[] ____cacheline_aligned_in_smp;
};

struct bpf_struct_ops_map {
        struct bpf_map map;
        struct rcu_head rcu;
        const struct bpf_struct_ops *st_ops;
        /* protect map_update */
        struct mutex lock;
        /* progs has all the bpf_prog that is populated
         * to the func ptr of the kernel's struct
         * (in kvalue.data).
         */
        struct bpf_prog **progs;
        /* image is a page that has all the trampolines
         * that stores the func args before calling the bpf_prog.
         * A PAGE_SIZE "image" is enough to store all trampoline for
         * "progs[]".
         */
        void *image;
        /* uvalue->data stores the kernel struct
         * (e.g. tcp_congestion_ops) that is more useful
         * to userspace than the kvalue.  For example,
         * the bpf_prog's id is stored instead of the kernel
         * address of a func ptr.
         */
        struct bpf_struct_ops_value *uvalue;
        /* kvalue.data stores the actual kernel's struct
         * (e.g. tcp_congestion_ops) that will be
         * registered to the kernel subsystem.
         */
        struct bpf_struct_ops_value kvalue;
};

#define VALUE_PREFIX "bpf_struct_ops_"
#define VALUE_PREFIX_LEN (sizeof(VALUE_PREFIX) - 1)

/* bpf_struct_ops_##_name (e.g. bpf_struct_ops_tcp_congestion_ops) is
 * the map's value exposed to the userspace and its btf-type-id is
 * stored at the map->btf_vmlinux_value_type_id.
 *
 */
#define BPF_STRUCT_OPS_TYPE(_name)                              \
extern struct bpf_struct_ops bpf_##_name;                       \
                                                                \
struct bpf_struct_ops_##_name {                                         \
        BPF_STRUCT_OPS_COMMON_VALUE;                            \
        struct _name data ____cacheline_aligned_in_smp;         \
};
#include "bpf_struct_ops_types.h"
#undef BPF_STRUCT_OPS_TYPE

enum {
#define BPF_STRUCT_OPS_TYPE(_name) BPF_STRUCT_OPS_TYPE_##_name,
#include "bpf_struct_ops_types.h"
#undef BPF_STRUCT_OPS_TYPE
        __NR_BPF_STRUCT_OPS_TYPE,
};

static struct bpf_struct_ops * const bpf_struct_ops[] = {
#define BPF_STRUCT_OPS_TYPE(_name)                              \
        [BPF_STRUCT_OPS_TYPE_##_name] = &bpf_##_name,
#include "bpf_struct_ops_types.h"
#undef BPF_STRUCT_OPS_TYPE
};

const struct bpf_verifier_ops bpf_struct_ops_verifier_ops = {
};

const struct bpf_prog_ops bpf_struct_ops_prog_ops = {
};

static const struct btf_type *module_type;

void bpf_struct_ops_init(struct btf *btf, struct bpf_verifier_log *log)
{
        s32 type_id, value_id, module_id;
        const struct btf_member *member;
        struct bpf_struct_ops *st_ops;
        const struct btf_type *t;
        char value_name[128];
        const char *mname;
        u32 i, j;

        /* Ensure BTF type is emitted for "struct bpf_struct_ops_##_name" */
#define BPF_STRUCT_OPS_TYPE(_name) BTF_TYPE_EMIT(struct bpf_struct_ops_##_name);
#include "bpf_struct_ops_types.h"
#undef BPF_STRUCT_OPS_TYPE

        module_id = btf_find_by_name_kind(btf, "module", BTF_KIND_STRUCT);
        if (module_id < 0) {
                pr_warn("Cannot find struct module in btf_vmlinux\n");
                return;
        }
        module_type = btf_type_by_id(btf, module_id);

        for (i = 0; i < ARRAY_SIZE(bpf_struct_ops); i++) {
                st_ops = bpf_struct_ops[i];

                if (strlen(st_ops->name) + VALUE_PREFIX_LEN >=
                    sizeof(value_name)) {
                        pr_warn("struct_ops name %s is too long\n",
                                st_ops->name);
                        continue;
                }
                sprintf(value_name, "%s%s", VALUE_PREFIX, st_ops->name);

                value_id = btf_find_by_name_kind(btf, value_name,
                                                 BTF_KIND_STRUCT);
                if (value_id < 0) {
                        pr_warn("Cannot find struct %s in btf_vmlinux\n",
                                value_name);
                        continue;
                }

                type_id = btf_find_by_name_kind(btf, st_ops->name,
                                                BTF_KIND_STRUCT);
                if (type_id < 0) {
                        pr_warn("Cannot find struct %s in btf_vmlinux\n",
                                st_ops->name);
                        continue;
                }
                t = btf_type_by_id(btf, type_id);
                if (btf_type_vlen(t) > BPF_STRUCT_OPS_MAX_NR_MEMBERS) {
                        pr_warn("Cannot support #%u members in struct %s\n",
                                btf_type_vlen(t), st_ops->name);
                        continue;
                }

                for_each_member(j, t, member) {
                        const struct btf_type *func_proto;

                        mname = btf_name_by_offset(btf, member->name_off);
                        if (!*mname) {
                                pr_warn("anon member in struct %s is not supported\n",
                                        st_ops->name);
                                break;
                        }

                        if (btf_member_bitfield_size(t, member)) {
                                pr_warn("bit field member %s in struct %s is not supported\n",
                                        mname, st_ops->name);
                                break;
                        }

                        func_proto = btf_type_resolve_func_ptr(btf,
                                                               member->type,
                                                               NULL);
                        if (func_proto &&
                            btf_distill_func_proto(log, btf,
                                                   func_proto, mname,
                                                   &st_ops->func_models[j])) {
                                pr_warn("Error in parsing func ptr %s in struct %s\n",
                                        mname, st_ops->name);
                                break;
                        }
                }

                if (j == btf_type_vlen(t)) {
                        if (st_ops->init(btf)) {
                                pr_warn("Error in init bpf_struct_ops %s\n",
                                        st_ops->name);
                        } else {
                                st_ops->type_id = type_id;
                                st_ops->type = t;
                                st_ops->value_id = value_id;
                                st_ops->value_type = btf_type_by_id(btf,
                                                                    value_id);
                        }
                }
        }
}

extern struct btf *btf_vmlinux;

static const struct bpf_struct_ops *
bpf_struct_ops_find_value(u32 value_id)
{
        unsigned int i;

        if (!value_id || !btf_vmlinux)
                return NULL;

        for (i = 0; i < ARRAY_SIZE(bpf_struct_ops); i++) {
                if (bpf_struct_ops[i]->value_id == value_id)
                        return bpf_struct_ops[i];
        }

        return NULL;
}

const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id)
{
        unsigned int i;

        if (!type_id || !btf_vmlinux)
                return NULL;

        for (i = 0; i < ARRAY_SIZE(bpf_struct_ops); i++) {
                if (bpf_struct_ops[i]->type_id == type_id)
                        return bpf_struct_ops[i];
        }

        return NULL;
}

static int bpf_struct_ops_map_get_next_key(struct bpf_map *map, void *key,
                                           void *next_key)
{
        if (key && *(u32 *)key == 0)
                return -ENOENT;

        *(u32 *)next_key = 0;
        return 0;
}

int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
                                       void *value)
{
        struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
        struct bpf_struct_ops_value *uvalue, *kvalue;
        enum bpf_struct_ops_state state;

        if (unlikely(*(u32 *)key != 0))
                return -ENOENT;

        kvalue = &st_map->kvalue;
        /* Pair with smp_store_release() during map_update */
        state = smp_load_acquire(&kvalue->state);
        if (state == BPF_STRUCT_OPS_STATE_INIT) {
                memset(value, 0, map->value_size);
                return 0;
        }

        /* No lock is needed.  state and refcnt do not need
         * to be updated together under atomic context.
         */
        uvalue = (struct bpf_struct_ops_value *)value;
        memcpy(uvalue, st_map->uvalue, map->value_size);
        uvalue->state = state;
        refcount_set(&uvalue->refcnt, refcount_read(&kvalue->refcnt));

        return 0;
}

static void *bpf_struct_ops_map_lookup_elem(struct bpf_map *map, void *key)
{
        return ERR_PTR(-EINVAL);
}

static void bpf_struct_ops_map_put_progs(struct bpf_struct_ops_map *st_map)
{
        const struct btf_type *t = st_map->st_ops->type;
        u32 i;

        for (i = 0; i < btf_type_vlen(t); i++) {
                if (st_map->progs[i]) {
                        bpf_prog_put(st_map->progs[i]);
                        st_map->progs[i] = NULL;
                }
        }
}

static int check_zero_holes(const struct btf_type *t, void *data)
{
        const struct btf_member *member;
        u32 i, moff, msize, prev_mend = 0;
        const struct btf_type *mtype;

        for_each_member(i, t, member) {
                moff = btf_member_bit_offset(t, member) / 8;
                if (moff > prev_mend &&
                    memchr_inv(data + prev_mend, 0, moff - prev_mend))
                        return -EINVAL;

                mtype = btf_type_by_id(btf_vmlinux, member->type);
                mtype = btf_resolve_size(btf_vmlinux, mtype, &msize);
                if (IS_ERR(mtype))
                        return PTR_ERR(mtype);
                prev_mend = moff + msize;
        }

        if (t->size > prev_mend &&
            memchr_inv(data + prev_mend, 0, t->size - prev_mend))
                return -EINVAL;

        return 0;
}

static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
                                          void *value, u64 flags)
{
        struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
        const struct bpf_struct_ops *st_ops = st_map->st_ops;
        struct bpf_struct_ops_value *uvalue, *kvalue;
        const struct btf_member *member;
        const struct btf_type *t = st_ops->type;
        struct bpf_tramp_progs *tprogs = NULL;
        void *udata, *kdata;
        int prog_fd, err = 0;
        void *image;
        u32 i;

        if (flags)
                return -EINVAL;

        if (*(u32 *)key != 0)
                return -E2BIG;

        err = check_zero_holes(st_ops->value_type, value);
        if (err)
                return err;

        uvalue = (struct bpf_struct_ops_value *)value;
        err = check_zero_holes(t, uvalue->data);
        if (err)
                return err;

        if (uvalue->state || refcount_read(&uvalue->refcnt))
                return -EINVAL;

        tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
        if (!tprogs)
                return -ENOMEM;

        uvalue = (struct bpf_struct_ops_value *)st_map->uvalue;
        kvalue = (struct bpf_struct_ops_value *)&st_map->kvalue;

        mutex_lock(&st_map->lock);

        if (kvalue->state != BPF_STRUCT_OPS_STATE_INIT) {
                err = -EBUSY;
                goto unlock;
        }

        memcpy(uvalue, value, map->value_size);

        udata = &uvalue->data;
        kdata = &kvalue->data;
        image = st_map->image;

        for_each_member(i, t, member) {
                const struct btf_type *mtype, *ptype;
                struct bpf_prog *prog;
                u32 moff;
                u32 flags;

                moff = btf_member_bit_offset(t, member) / 8;
                ptype = btf_type_resolve_ptr(btf_vmlinux, member->type, NULL);
                if (ptype == module_type) {
                        if (*(void **)(udata + moff))
                                goto reset_unlock;
                        *(void **)(kdata + moff) = BPF_MODULE_OWNER;
                        continue;
                }

                err = st_ops->init_member(t, member, kdata, udata);
                if (err < 0)
                        goto reset_unlock;

                /* The ->init_member() has handled this member */
                if (err > 0)
                        continue;

                /* If st_ops->init_member does not handle it,
                 * we will only handle func ptrs and zero-ed members
                 * here.  Reject everything else.
                 */

                /* All non func ptr member must be 0 */
                if (!ptype || !btf_type_is_func_proto(ptype)) {
                        u32 msize;

                        mtype = btf_type_by_id(btf_vmlinux, member->type);
                        mtype = btf_resolve_size(btf_vmlinux, mtype, &msize);
                        if (IS_ERR(mtype)) {
                                err = PTR_ERR(mtype);
                                goto reset_unlock;
                        }

                        if (memchr_inv(udata + moff, 0, msize)) {
                                err = -EINVAL;
                                goto reset_unlock;
                        }

                        continue;
                }

                prog_fd = (int)(*(unsigned long *)(udata + moff));
                /* Similar check as the attr->attach_prog_fd */
                if (!prog_fd)
                        continue;

                prog = bpf_prog_get(prog_fd);
                if (IS_ERR(prog)) {
                        err = PTR_ERR(prog);
                        goto reset_unlock;
                }
                st_map->progs[i] = prog;

                if (prog->type != BPF_PROG_TYPE_STRUCT_OPS ||
                    prog->aux->attach_btf_id != st_ops->type_id ||
                    prog->expected_attach_type != i) {
                        err = -EINVAL;
                        goto reset_unlock;
                }

                tprogs[BPF_TRAMP_FENTRY].progs[0] = prog;
                tprogs[BPF_TRAMP_FENTRY].nr_progs = 1;
                flags = st_ops->func_models[i].ret_size > 0 ?
                        BPF_TRAMP_F_RET_FENTRY_RET : 0;
                err = arch_prepare_bpf_trampoline(NULL, image,
                                                  st_map->image + PAGE_SIZE,
                                                  &st_ops->func_models[i],
                                                  flags, tprogs, NULL);
                if (err < 0)
                        goto reset_unlock;

                *(void **)(kdata + moff) = image;
                image += err;

                /* put prog_id to udata */
                *(unsigned long *)(udata + moff) = prog->aux->id;
        }

        refcount_set(&kvalue->refcnt, 1);
        bpf_map_inc(map);

        set_memory_ro((long)st_map->image, 1);
        set_memory_x((long)st_map->image, 1);
        err = st_ops->reg(kdata);
        if (likely(!err)) {
                /* Pair with smp_load_acquire() during lookup_elem().
                 * It ensures the above udata updates (e.g. prog->aux->id)
                 * can be seen once BPF_STRUCT_OPS_STATE_INUSE is set.
                 */
                smp_store_release(&kvalue->state, BPF_STRUCT_OPS_STATE_INUSE);
                goto unlock;
        }

        /* Error during st_ops->reg().  It is very unlikely since
         * the above init_member() should have caught it earlier
         * before reg().  The only possibility is if there was a race
         * in registering the struct_ops (under the same name) to
         * a sub-system through different struct_ops's maps.
         */
        set_memory_nx((long)st_map->image, 1);
        set_memory_rw((long)st_map->image, 1);
        bpf_map_put(map);

reset_unlock:
        bpf_struct_ops_map_put_progs(st_map);
        memset(uvalue, 0, map->value_size);
        memset(kvalue, 0, map->value_size);
unlock:
        kfree(tprogs);
        mutex_unlock(&st_map->lock);
        return err;
}

static int bpf_struct_ops_map_delete_elem(struct bpf_map *map, void *key)
{
        enum bpf_struct_ops_state prev_state;
        struct bpf_struct_ops_map *st_map;

        st_map = (struct bpf_struct_ops_map *)map;
        prev_state = cmpxchg(&st_map->kvalue.state,
                             BPF_STRUCT_OPS_STATE_INUSE,
                             BPF_STRUCT_OPS_STATE_TOBEFREE);
        switch (prev_state) {
        case BPF_STRUCT_OPS_STATE_INUSE:
                st_map->st_ops->unreg(&st_map->kvalue.data);
                if (refcount_dec_and_test(&st_map->kvalue.refcnt))
                        bpf_map_put(map);
                return 0;
        case BPF_STRUCT_OPS_STATE_TOBEFREE:
                return -EINPROGRESS;
        case BPF_STRUCT_OPS_STATE_INIT:
                return -ENOENT;
        default:
                WARN_ON_ONCE(1);
                /* Should never happen.  Treat it as not found. */
                return -ENOENT;
        }
}

static void bpf_struct_ops_map_seq_show_elem(struct bpf_map *map, void *key,
                                             struct seq_file *m)
{
        void *value;
        int err;

        value = kmalloc(map->value_size, GFP_USER | __GFP_NOWARN);
        if (!value)
                return;

        err = bpf_struct_ops_map_sys_lookup_elem(map, key, value);
        if (!err) {
                btf_type_seq_show(btf_vmlinux, map->btf_vmlinux_value_type_id,
                                  value, m);
                seq_puts(m, "\n");
        }

        kfree(value);
}

static void bpf_struct_ops_map_free(struct bpf_map *map)
{
        struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;

        if (st_map->progs)
                bpf_struct_ops_map_put_progs(st_map);
        bpf_map_area_free(st_map->progs);
        bpf_jit_free_exec(st_map->image);
        bpf_map_area_free(st_map->uvalue);
        bpf_map_area_free(st_map);
}

static int bpf_struct_ops_map_alloc_check(union bpf_attr *attr)
{
        if (attr->key_size != sizeof(unsigned int) || attr->max_entries != 1 ||
            attr->map_flags || !attr->btf_vmlinux_value_type_id)
                return -EINVAL;
        return 0;
}

static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr)
{
        const struct bpf_struct_ops *st_ops;
        size_t st_map_size;
        struct bpf_struct_ops_map *st_map;
        const struct btf_type *t, *vt;
        struct bpf_map *map;

        if (!bpf_capable())
                return ERR_PTR(-EPERM);

        st_ops = bpf_struct_ops_find_value(attr->btf_vmlinux_value_type_id);
        if (!st_ops)
                return ERR_PTR(-ENOTSUPP);

        vt = st_ops->value_type;
        if (attr->value_size != vt->size)
                return ERR_PTR(-EINVAL);

        t = st_ops->type;

        st_map_size = sizeof(*st_map) +
                /* kvalue stores the
                 * struct bpf_struct_ops_tcp_congestions_ops
                 */
                (vt->size - sizeof(struct bpf_struct_ops_value));

        st_map = bpf_map_area_alloc(st_map_size, NUMA_NO_NODE);
        if (!st_map)
                return ERR_PTR(-ENOMEM);

        st_map->st_ops = st_ops;
        map = &st_map->map;

        st_map->uvalue = bpf_map_area_alloc(vt->size, NUMA_NO_NODE);
        st_map->progs =
                bpf_map_area_alloc(btf_type_vlen(t) * sizeof(struct bpf_prog *),
                                   NUMA_NO_NODE);
        st_map->image = bpf_jit_alloc_exec(PAGE_SIZE);
        if (!st_map->uvalue || !st_map->progs || !st_map->image) {
                bpf_struct_ops_map_free(map);
                return ERR_PTR(-ENOMEM);
        }

        mutex_init(&st_map->lock);
        set_vm_flush_reset_perms(st_map->image);
        bpf_map_init_from_attr(map, attr);

        return map;
}

static int bpf_struct_ops_map_btf_id;
const struct bpf_map_ops bpf_struct_ops_map_ops = {
        .map_alloc_check = bpf_struct_ops_map_alloc_check,
        .map_alloc = bpf_struct_ops_map_alloc,
        .map_free = bpf_struct_ops_map_free,
        .map_get_next_key = bpf_struct_ops_map_get_next_key,
        .map_lookup_elem = bpf_struct_ops_map_lookup_elem,
        .map_delete_elem = bpf_struct_ops_map_delete_elem,
        .map_update_elem = bpf_struct_ops_map_update_elem,
        .map_seq_show_elem = bpf_struct_ops_map_seq_show_elem,
        .map_btf_name = "bpf_struct_ops_map",
        .map_btf_id = &bpf_struct_ops_map_btf_id,
};

/* "const void *" because some subsystem is
 * passing a const (e.g. const struct tcp_congestion_ops *)
 */
bool bpf_struct_ops_get(const void *kdata)
{
        struct bpf_struct_ops_value *kvalue;

        kvalue = container_of(kdata, struct bpf_struct_ops_value, data);

        return refcount_inc_not_zero(&kvalue->refcnt);
}

static void bpf_struct_ops_put_rcu(struct rcu_head *head)
{
        struct bpf_struct_ops_map *st_map;

        st_map = container_of(head, struct bpf_struct_ops_map, rcu);
        bpf_map_put(&st_map->map);
}

void bpf_struct_ops_put(const void *kdata)
{
        struct bpf_struct_ops_value *kvalue;

        kvalue = container_of(kdata, struct bpf_struct_ops_value, data);
        if (refcount_dec_and_test(&kvalue->refcnt)) {
                struct bpf_struct_ops_map *st_map;

                st_map = container_of(kvalue, struct bpf_struct_ops_map,
                                      kvalue);
                /* The struct_ops's function may switch to another struct_ops.
                 *
                 * For example, bpf_tcp_cc_x->init() may switch to
                 * another tcp_cc_y by calling
                 * setsockopt(TCP_CONGESTION, "tcp_cc_y").
                 * During the switch,  bpf_struct_ops_put(tcp_cc_x) is called
                 * and its map->refcnt may reach 0 which then free its
                 * trampoline image while tcp_cc_x is still running.
                 *
                 * Thus, a rcu grace period is needed here.
                 */
                call_rcu(&st_map->rcu, bpf_struct_ops_put_rcu);
        }
}