// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2019 Facebook */
#include <linux/hash.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/ftrace.h>
#include <linux/rbtree_latch.h>
#include <linux/perf_event.h>
#include <linux/btf.h>

/* dummy _ops. The verifier will operate on target program's ops. */
const struct bpf_verifier_ops bpf_extension_verifier_ops = {
};
const struct bpf_prog_ops bpf_extension_prog_ops = {
};

/* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */
#define TRAMPOLINE_HASH_BITS 10
#define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)

static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];

/* serializes access to trampoline_table */
static DEFINE_MUTEX(trampoline_mutex);

void *bpf_jit_alloc_exec_page(void)
{
        void *image;

        image = bpf_jit_alloc_exec(PAGE_SIZE);
        if (!image)
                return NULL;

        set_vm_flush_reset_perms(image);
        /* Keep image as writeable. The alternative is to keep flipping ro/rw
         * everytime new program is attached or detached.
         */
        set_memory_x((long)image, 1);
        return image;
}

void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym)
{
        ksym->start = (unsigned long) data;
        ksym->end = ksym->start + PAGE_SIZE;
        bpf_ksym_add(ksym);
        perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
                           PAGE_SIZE, false, ksym->name);
}

void bpf_image_ksym_del(struct bpf_ksym *ksym)
{
        bpf_ksym_del(ksym);
        perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
                           PAGE_SIZE, true, ksym->name);
}

static void bpf_trampoline_ksym_add(struct bpf_trampoline *tr)
{
        struct bpf_ksym *ksym = &tr->ksym;

        snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu", tr->key);
        bpf_image_ksym_add(tr->image, ksym);
}

struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
{
        struct bpf_trampoline *tr;
        struct hlist_head *head;
        void *image;
        int i;

        mutex_lock(&trampoline_mutex);
        head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
        hlist_for_each_entry(tr, head, hlist) {
                if (tr->key == key) {
                        refcount_inc(&tr->refcnt);
                        goto out;
                }
        }
        tr = kzalloc(sizeof(*tr), GFP_KERNEL);
        if (!tr)
                goto out;

        /* is_root was checked earlier. No need for bpf_jit_charge_modmem() */
        image = bpf_jit_alloc_exec_page();
        if (!image) {
                kfree(tr);
                tr = NULL;
                goto out;
        }

        tr->key = key;
        INIT_HLIST_NODE(&tr->hlist);
        hlist_add_head(&tr->hlist, head);
        refcount_set(&tr->refcnt, 1);
        mutex_init(&tr->mutex);
        for (i = 0; i < BPF_TRAMP_MAX; i++)
                INIT_HLIST_HEAD(&tr->progs_hlist[i]);
        tr->image = image;
        INIT_LIST_HEAD_RCU(&tr->ksym.lnode);
        bpf_trampoline_ksym_add(tr);
out:
        mutex_unlock(&trampoline_mutex);
        return tr;
}

static int is_ftrace_location(void *ip)
{
        long addr;

        addr = ftrace_location((long)ip);
        if (!addr)
                return 0;
        if (WARN_ON_ONCE(addr != (long)ip))
                return -EFAULT;
        return 1;
}

static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
{
        void *ip = tr->func.addr;
        int ret;

        if (tr->func.ftrace_managed)
                ret = unregister_ftrace_direct((long)ip, (long)old_addr);
        else
                ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
        return ret;
}

static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
{
        void *ip = tr->func.addr;
        int ret;

        if (tr->func.ftrace_managed)
                ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
        else
                ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
        return ret;
}

/* first time registering */
static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
{
        void *ip = tr->func.addr;
        int ret;

        ret = is_ftrace_location(ip);
        if (ret < 0)
                return ret;
        tr->func.ftrace_managed = ret;

        if (tr->func.ftrace_managed)
                ret = register_ftrace_direct((long)ip, (long)new_addr);
        else
                ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
        return ret;
}

static struct bpf_tramp_progs *
bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total)
{
        const struct bpf_prog_aux *aux;
        struct bpf_tramp_progs *tprogs;
        struct bpf_prog **progs;
        int kind;

        *total = 0;
        tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
        if (!tprogs)
                return ERR_PTR(-ENOMEM);

        for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
                tprogs[kind].nr_progs = tr->progs_cnt[kind];
                *total += tr->progs_cnt[kind];
                progs = tprogs[kind].progs;

                hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist)
                        *progs++ = aux->prog;
        }
        return tprogs;
}

static int bpf_trampoline_update(struct bpf_trampoline *tr)
{
        void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
        void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
        struct bpf_tramp_progs *tprogs;
        u32 flags = BPF_TRAMP_F_RESTORE_REGS;
        int err, total;

        tprogs = bpf_trampoline_get_progs(tr, &total);
        if (IS_ERR(tprogs))
                return PTR_ERR(tprogs);

        if (total == 0) {
                err = unregister_fentry(tr, old_image);
                tr->selector = 0;
                goto out;
        }

        if (tprogs[BPF_TRAMP_FEXIT].nr_progs ||
            tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs)
                flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

        /* Though the second half of trampoline page is unused a task could be
         * preempted in the middle of the first half of trampoline and two
         * updates to trampoline would change the code from underneath the
         * preempted task. Hence wait for tasks to voluntarily schedule or go
         * to userspace.
         */

        synchronize_rcu_tasks();

        err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2,
                                          &tr->func.model, flags, tprogs,
                                          tr->func.addr);
        if (err < 0)
                goto out;

        if (tr->selector)
                /* progs already running at this address */
                err = modify_fentry(tr, old_image, new_image);
        else
                /* first time registering */
                err = register_fentry(tr, new_image);
        if (err)
                goto out;
        tr->selector++;
out:
        kfree(tprogs);
        return err;
}

static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
{
        switch (prog->expected_attach_type) {
        case BPF_TRACE_FENTRY:
                return BPF_TRAMP_FENTRY;
        case BPF_MODIFY_RETURN:
                return BPF_TRAMP_MODIFY_RETURN;
        case BPF_TRACE_FEXIT:
                return BPF_TRAMP_FEXIT;
        case BPF_LSM_MAC:
                if (!prog->aux->attach_func_proto->type)
                        /* The function returns void, we cannot modify its
                         * return value.
                         */
                        return BPF_TRAMP_FEXIT;
                else
                        return BPF_TRAMP_MODIFY_RETURN;
        default:
                return BPF_TRAMP_REPLACE;
        }
}

int bpf_trampoline_link_prog(struct bpf_prog *prog)
{
        enum bpf_tramp_prog_type kind;
        struct bpf_trampoline *tr;
        int err = 0;
        int cnt;

        tr = prog->aux->trampoline;
        kind = bpf_attach_type_to_tramp(prog);
        mutex_lock(&tr->mutex);
        if (tr->extension_prog) {
                /* cannot attach fentry/fexit if extension prog is attached.
                 * cannot overwrite extension prog either.
                 */
                err = -EBUSY;
                goto out;
        }
        cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT];
        if (kind == BPF_TRAMP_REPLACE) {
                /* Cannot attach extension if fentry/fexit are in use. */
                if (cnt) {
                        err = -EBUSY;
                        goto out;
                }
                tr->extension_prog = prog;
                err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL,
                                         prog->bpf_func);
                goto out;
        }
        if (cnt >= BPF_MAX_TRAMP_PROGS) {
                err = -E2BIG;
                goto out;
        }
        if (!hlist_unhashed(&prog->aux->tramp_hlist)) {
                /* prog already linked */
                err = -EBUSY;
                goto out;
        }
        hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]);
        tr->progs_cnt[kind]++;
        err = bpf_trampoline_update(prog->aux->trampoline);
        if (err) {
                hlist_del(&prog->aux->tramp_hlist);
                tr->progs_cnt[kind]--;
        }
out:
        mutex_unlock(&tr->mutex);
        return err;
}

/* bpf_trampoline_unlink_prog() should never fail. */
int bpf_trampoline_unlink_prog(struct bpf_prog *prog)
{
        enum bpf_tramp_prog_type kind;
        struct bpf_trampoline *tr;
        int err;

        tr = prog->aux->trampoline;
        kind = bpf_attach_type_to_tramp(prog);
        mutex_lock(&tr->mutex);
        if (kind == BPF_TRAMP_REPLACE) {
                WARN_ON_ONCE(!tr->extension_prog);
                err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP,
                                         tr->extension_prog->bpf_func, NULL);
                tr->extension_prog = NULL;
                goto out;
        }
        hlist_del(&prog->aux->tramp_hlist);
        tr->progs_cnt[kind]--;
        err = bpf_trampoline_update(prog->aux->trampoline);
out:
        mutex_unlock(&tr->mutex);
        return err;
}

void bpf_trampoline_put(struct bpf_trampoline *tr)
{
        if (!tr)
                return;
        mutex_lock(&trampoline_mutex);
        if (!refcount_dec_and_test(&tr->refcnt))
                goto out;
        WARN_ON_ONCE(mutex_is_locked(&tr->mutex));
        if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY])))
                goto out;
        if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
                goto out;
        bpf_image_ksym_del(&tr->ksym);
        /* wait for tasks to get out of trampoline before freeing it */
        synchronize_rcu_tasks();
        bpf_jit_free_exec(tr->image);
        hlist_del(&tr->hlist);
        kfree(tr);
out:
        mutex_unlock(&trampoline_mutex);
}

/* The logic is similar to BPF_PROG_RUN, but with an explicit
 * rcu_read_lock() and migrate_disable() which are required
 * for the trampoline. The macro is split into
 * call _bpf_prog_enter
 * call prog->bpf_func
 * call __bpf_prog_exit
 */
u64 notrace __bpf_prog_enter(void)
        __acquires(RCU)
{
        u64 start = 0;

        rcu_read_lock();
        migrate_disable();
        if (static_branch_unlikely(&bpf_stats_enabled_key))
                start = sched_clock();
        return start;
}

void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start)
        __releases(RCU)
{
        struct bpf_prog_stats *stats;

        if (static_branch_unlikely(&bpf_stats_enabled_key) &&
            /* static_key could be enabled in __bpf_prog_enter
             * and disabled in __bpf_prog_exit.
             * And vice versa.
             * Hence check that 'start' is not zero.
             */
            start) {
                stats = this_cpu_ptr(prog->aux->stats);
                u64_stats_update_begin(&stats->syncp);
                stats->cnt++;
                stats->nsecs += sched_clock() - start;
                u64_stats_update_end(&stats->syncp);
        }
        migrate_enable();
        rcu_read_unlock();
}

int __weak
arch_prepare_bpf_trampoline(void *image, void *image_end,
                            const struct btf_func_model *m, u32 flags,
                            struct bpf_tramp_progs *tprogs,
                            void *orig_call)
{
        return -ENOTSUPP;
}

static int __init init_trampolines(void)
{
        int i;

        for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
                INIT_HLIST_HEAD(&trampoline_table[i]);
        return 0;
}
late_initcall(init_trampolines);