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
bpf_arch_text_poke error return value.
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 BUG_ON.
The problem is that in such case we won't update the tail call jump
and cause imballance 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 calling directly __bpf_arch_text_poke and skipping the bpf
symbol check like we do in bpf_tail_call_direct_fixup. This way the
prog_array_map_poke_run does not depend on bpf program having the kallsym
symbol in place.
[0] https://syzkaller.appspot.com/bug?extid=97a4fe20470e9bc30810
Cc: Lee Jones <lee@xxxxxxxxxx>
Cc: Maciej Fijalkowski <maciej.fijalkowski@xxxxxxxxx>
Fixes: ebf7d1f508a7 ("bpf, x64: rework pro/epilogue and tailcall handling in JIT")
Reported-by: syzbot+97a4fe20470e9bc30810@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: Lee Jones <lee@xxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 4 ++--
include/linux/bpf.h | 2 ++
kernel/bpf/arraymap.c | 31 +++++++++++--------------------
3 files changed, 15 insertions(+), 22 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 8c10d9abc239..35c2988caf29 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -391,8 +391,8 @@ static int emit_jump(u8 **pprog, void *func, void *ip)
return emit_patch(pprog, func, ip, 0xE9);
}
-static int __bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
- void *old_addr, void *new_addr)
+int __bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
+ void *old_addr, void *new_addr)
{
const u8 *nop_insn = x86_nops[5];
u8 old_insn[X86_PATCH_SIZE];
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 6762dac3ef76..c28a8563e845 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3174,6 +3174,8 @@ enum bpf_text_poke_type {
int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
void *addr1, void *addr2);
+int __bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
+ void *old_addr, void *new_addr);
void *bpf_arch_text_copy(void *dst, void *src, size_t len);
int bpf_arch_text_invalidate(void *dst, size_t len);
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 2058e89b5ddd..0b5afa2ec17a 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -1044,20 +1044,11 @@ 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()
+ * buffer is freed.
+ * 4) Any error happening below from __bpf_arch_text_poke()
* is a unexpected bug.
*/
if (!READ_ONCE(poke->tailcall_target_stable))
@@ -1073,33 +1064,33 @@ static void prog_array_map_poke_run(struct bpf_map *map, u32 key,
new_addr = new ? (u8 *)new->bpf_func + poke->adj_off : NULL;
if (new) {
- ret = bpf_arch_text_poke(poke->tailcall_target,
+ ret = __bpf_arch_text_poke(poke->tailcall_target,
BPF_MOD_JUMP,
old_addr, new_addr);
- BUG_ON(ret < 0 && ret != -EINVAL);
+ BUG_ON(ret < 0);
if (!old) {
- ret = bpf_arch_text_poke(poke->tailcall_bypass,
+ ret = __bpf_arch_text_poke(poke->tailcall_bypass,
BPF_MOD_JUMP,
poke->bypass_addr,
NULL);
- BUG_ON(ret < 0 && ret != -EINVAL);
+ BUG_ON(ret < 0);
}
} else {
- ret = bpf_arch_text_poke(poke->tailcall_bypass,
+ ret = __bpf_arch_text_poke(poke->tailcall_bypass,
BPF_MOD_JUMP,
old_bypass_addr,
poke->bypass_addr);
- BUG_ON(ret < 0 && ret != -EINVAL);
+ 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,
+ ret = __bpf_arch_text_poke(poke->tailcall_target,
BPF_MOD_JUMP,
old_addr, NULL);
- BUG_ON(ret < 0 && ret != -EINVAL);
+ BUG_ON(ret < 0);
}
}
}
--
2.43.0
