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bpf: Fix prog_array_map_poke_run map poke update 

Lee pointed out issue found by syscaller [0] hitting BUG in prog array
map poke update in prog_array_map_poke_run function due to error value
returned from bpf_arch_text_poke function.

There's race window where bpf_arch_text_poke can fail due to missing
bpf program kallsym symbols, which is accounted for with check for
-EINVAL in that BUG_ON call.

The problem is that in such case we won't update the tail call jump
and cause imbalance for the next tail call update check which will
fail with -EBUSY in bpf_arch_text_poke.

I'm hitting following race during the program load:

  CPU 0                             CPU 1

  bpf_prog_load
    bpf_check
      do_misc_fixups
        prog_array_map_poke_track

                                    map_update_elem
                                      bpf_fd_array_map_update_elem
                                        prog_array_map_poke_run

                                          bpf_arch_text_poke returns -EINVAL

    bpf_prog_kallsyms_add

After bpf_arch_text_poke (CPU 1) fails to update the tail call jump, the next
poke update fails on expected jump instruction check in bpf_arch_text_poke
with -EBUSY and triggers the BUG_ON in prog_array_map_poke_run.

Similar race exists on the program unload.

Fixing this by moving the update to bpf_arch_poke_desc_update function which
makes sure we call __bpf_arch_text_poke that skips the bpf address check.

Each architecture has slightly different approach wrt looking up bpf address
in bpf_arch_text_poke, so instead of splitting the function or adding new
'checkip' argument in previous version, it seems best to move the whole
map_poke_run update as arch specific code.

  [0] https://syzkaller.appspot.com/bug?extid=97a4fe20470e9bc30810

Fixes: ebf7d1f508 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT")
Reported-by: syzbot+97a4fe20470e9bc30810@syzkaller.appspotmail.com
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Cc: Lee Jones <lee@kernel.org>
Cc: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Link: https://lore.kernel.org/bpf/20231206083041.1306660-2-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2023-12-06 09:30:40 +01:00 committed by Daniel Borkmann
parent e4d008d49a
commit 4b7de80160
3 changed files with 59 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

46
arch/x86/net/bpf_jit_comp.c
View File

@ -3025,3 +3025,49 @@ void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp
#endif
WARN(1, "verification of programs using bpf_throw should have failed\n");
}
void bpf_arch_poke_desc_update(struct bpf_jit_poke_descriptor *poke,
struct bpf_prog *new, struct bpf_prog *old)
{
u8 *old_addr, *new_addr, *old_bypass_addr;
int ret;
old_bypass_addr = old ? NULL : poke->bypass_addr;
old_addr = old ? (u8 *)old->bpf_func + poke->adj_off : NULL;
new_addr = new ? (u8 *)new->bpf_func + poke->adj_off : NULL;
/*
* On program loading or teardown, the program's kallsym entry
* might not be in place, so we use __bpf_arch_text_poke to skip
* the kallsyms check.
*/
if (new) {
ret = __bpf_arch_text_poke(poke->tailcall_target,
BPF_MOD_JUMP,
old_addr, new_addr);
BUG_ON(ret < 0);
if (!old) {
ret = __bpf_arch_text_poke(poke->tailcall_bypass,
BPF_MOD_JUMP,
poke->bypass_addr,
NULL);
BUG_ON(ret < 0);
}
} else {
ret = __bpf_arch_text_poke(poke->tailcall_bypass,
BPF_MOD_JUMP,
old_bypass_addr,
poke->bypass_addr);
BUG_ON(ret < 0);
/* let other CPUs finish the execution of program
* so that it will not possible to expose them
* to invalid nop, stack unwind, nop state
*/
if (!ret)
synchronize_rcu();
ret = __bpf_arch_text_poke(poke->tailcall_target,
BPF_MOD_JUMP,
old_addr, NULL);
BUG_ON(ret < 0);
}
}

3
include/linux/bpf.h
View File

@ -3175,6 +3175,9 @@ enum bpf_text_poke_type {
int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
void *addr1, void *addr2);
void bpf_arch_poke_desc_update(struct bpf_jit_poke_descriptor *poke,
struct bpf_prog *new, struct bpf_prog *old);
void *bpf_arch_text_copy(void *dst, void *src, size_t len);
int bpf_arch_text_invalidate(void *dst, size_t len);

58
kernel/bpf/arraymap.c
View File

@ -1012,11 +1012,16 @@ static void prog_array_map_poke_untrack(struct bpf_map *map,
mutex_unlock(&aux->poke_mutex);
}
void __weak bpf_arch_poke_desc_update(struct bpf_jit_poke_descriptor *poke,
struct bpf_prog *new, struct bpf_prog *old)
{
WARN_ON_ONCE(1);
}
static void prog_array_map_poke_run(struct bpf_map *map, u32 key,
struct bpf_prog *old,
struct bpf_prog *new)
{
u8 *old_addr, *new_addr, *old_bypass_addr;
struct prog_poke_elem *elem;
struct bpf_array_aux *aux;
@ -1025,7 +1030,7 @@ static void prog_array_map_poke_run(struct bpf_map *map, u32 key,
list_for_each_entry(elem, &aux->poke_progs, list) {
struct bpf_jit_poke_descriptor *poke;
int i, ret;
int i;
for (i = 0; i < elem->aux->size_poke_tab; i++) {
poke = &elem->aux->poke_tab[i];
@ -1044,21 +1049,10 @@ static void prog_array_map_poke_run(struct bpf_map *map, u32 key,
* activated, so tail call updates can arrive from here
* while JIT is still finishing its final fixup for
* non-activated poke entries.
* 3) On program teardown, the program's kallsym entry gets
* removed out of RCU callback, but we can only untrack
* from sleepable context, therefore bpf_arch_text_poke()
* might not see that this is in BPF text section and
* bails out with -EINVAL. As these are unreachable since
* RCU grace period already passed, we simply skip them.
* 4) Also programs reaching refcount of zero while patching
* 3) Also programs reaching refcount of zero while patching
* is in progress is okay since we're protected under
* poke_mutex and untrack the programs before the JIT
* buffer is freed. When we're still in the middle of
* patching and suddenly kallsyms entry of the program
* gets evicted, we just skip the rest which is fine due
* to point 3).
* 5) Any other error happening below from bpf_arch_text_poke()
* is a unexpected bug.
* buffer is freed.
*/
if (!READ_ONCE(poke->tailcall_target_stable))
continue;
@ -1068,39 +1062,7 @@ static void prog_array_map_poke_run(struct bpf_map *map, u32 key,
poke->tail_call.key != key)
continue;
old_bypass_addr = old ? NULL : poke->bypass_addr;
old_addr = old ? (u8 *)old->bpf_func + poke->adj_off : NULL;
new_addr = new ? (u8 *)new->bpf_func + poke->adj_off : NULL;
if (new) {
ret = bpf_arch_text_poke(poke->tailcall_target,
BPF_MOD_JUMP,
old_addr, new_addr);
BUG_ON(ret < 0 && ret != -EINVAL);
if (!old) {
ret = bpf_arch_text_poke(poke->tailcall_bypass,
BPF_MOD_JUMP,
poke->bypass_addr,
NULL);
BUG_ON(ret < 0 && ret != -EINVAL);
}
} else {
ret = bpf_arch_text_poke(poke->tailcall_bypass,
BPF_MOD_JUMP,
old_bypass_addr,
poke->bypass_addr);
BUG_ON(ret < 0 && ret != -EINVAL);
/* let other CPUs finish the execution of program
* so that it will not possible to expose them
* to invalid nop, stack unwind, nop state
*/
if (!ret)
synchronize_rcu();
ret = bpf_arch_text_poke(poke->tailcall_target,
BPF_MOD_JUMP,
old_addr, NULL);
BUG_ON(ret < 0 && ret != -EINVAL);
}
bpf_arch_poke_desc_update(poke, new, old);
}
}
}