blob: 7e89f1f49d7712d6f530bba2c6572b57ae702b1f [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2019 Facebook */
#include <linux/hash.h>
#include <linux/bpf.h>
#include <linux/filter.h>
/* 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);
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_SIZE);
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]);
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);
tr->image = image;
out:
mutex_unlock(&trampoline_mutex);
return tr;
}
/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
* bytes on x86. Pick a number to fit into PAGE_SIZE / 2
*/
#define BPF_MAX_TRAMP_PROGS 40
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_prog *progs_to_run[BPF_MAX_TRAMP_PROGS];
int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY];
int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT];
struct bpf_prog **progs, **fentry, **fexit;
u32 flags = BPF_TRAMP_F_RESTORE_REGS;
struct bpf_prog_aux *aux;
int err;
if (fentry_cnt + fexit_cnt == 0) {
err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL,
old_image, NULL);
tr->selector = 0;
goto out;
}
/* populate fentry progs */
fentry = progs = progs_to_run;
hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist)
*progs++ = aux->prog;
/* populate fexit progs */
fexit = progs;
hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist)
*progs++ = aux->prog;
if (fexit_cnt)
flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
err = arch_prepare_bpf_trampoline(new_image, &tr->func.model, flags,
fentry, fentry_cnt,
fexit, fexit_cnt,
tr->func.addr);
if (err)
goto out;
if (tr->selector)
/* progs already running at this address */
err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL,
old_image, new_image);
else
/* first time registering */
err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL, NULL,
new_image);
if (err)
goto out;
tr->selector++;
out:
return err;
}
static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t)
{
switch (t) {
case BPF_TRACE_FENTRY:
return BPF_TRAMP_FENTRY;
default:
return BPF_TRAMP_FEXIT;
}
}
int bpf_trampoline_link_prog(struct bpf_prog *prog)
{
enum bpf_tramp_prog_type kind;
struct bpf_trampoline *tr;
int err = 0;
tr = prog->aux->trampoline;
kind = bpf_attach_type_to_tramp(prog->expected_attach_type);
mutex_lock(&tr->mutex);
if (tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT]
>= 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->expected_attach_type);
mutex_lock(&tr->mutex);
hlist_del(&prog->aux->tramp_hlist);
tr->progs_cnt[kind]--;
err = bpf_trampoline_update(prog->aux->trampoline);
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_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 explicit rcu and preempt that
* are needed for trampoline. The macro is split into
* call _bpf_prog_enter
* call prog->bpf_func
* call __bpf_prog_exit
*/
u64 notrace __bpf_prog_enter(void)
{
u64 start = 0;
rcu_read_lock();
preempt_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)
{
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);
}
preempt_enable();
rcu_read_unlock();
}
int __weak
arch_prepare_bpf_trampoline(void *image, struct btf_func_model *m, u32 flags,
struct bpf_prog **fentry_progs, int fentry_cnt,
struct bpf_prog **fexit_progs, int fexit_cnt,
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);