linux-kernel - [PATCH bpf-next] bpf: Fix WARN() in get_bpf_raw_tp

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Message-Id: <20250513042747.757042-1-chen.dylane@linux.dev>
Date: Tue, 13 May 2025 12:27:47 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	rostedt@...dmis.org,
	mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com,
	mmullins@...com
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Tao Chen <chen.dylane@...ux.dev>,
	syzbot+45b0c89a0fc7ae8dbadc@...kaller.appspotmail.com
Subject: [PATCH bpf-next] bpf: Fix WARN() in get_bpf_raw_tp_regs

syzkaller reported an issue:

WARNING: CPU: 3 PID: 5971 at kernel/trace/bpf_trace.c:1861 get_bpf_raw_tp_regs+0xa4/0x100 kernel/trace/bpf_trace.c:1861
Modules linked in:
CPU: 3 UID: 0 PID: 5971 Comm: syz-executor205 Not tainted 6.15.0-rc5-syzkaller-00038-g707df3375124 #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:get_bpf_raw_tp_regs+0xa4/0x100 kernel/trace/bpf_trace.c:1861
RSP: 0018:ffffc90003636fa8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000003 RCX: ffffffff81c6bc4c
RDX: ffff888032efc880 RSI: ffffffff81c6bc83 RDI: 0000000000000005
RBP: ffff88806a730860 R08: 0000000000000005 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000000 R12: 0000000000000004
R13: 0000000000000001 R14: ffffc90003637008 R15: 0000000000000900
FS:  0000000000000000(0000) GS:ffff8880d6cdf000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7baee09130 CR3: 0000000029f5a000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ____bpf_get_stack_raw_tp kernel/trace/bpf_trace.c:1934 [inline]
 bpf_get_stack_raw_tp+0x24/0x160 kernel/trace/bpf_trace.c:1931
 bpf_prog_ec3b2eefa702d8d3+0x43/0x47
 bpf_dispatcher_nop_func include/linux/bpf.h:1316 [inline]
 __bpf_prog_run include/linux/filter.h:718 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 __bpf_trace_run kernel/trace/bpf_trace.c:2363 [inline]
 bpf_trace_run3+0x23f/0x5a0 kernel/trace/bpf_trace.c:2405
 __bpf_trace_mmap_lock_acquire_returned+0xfc/0x140 include/trace/events/mmap_lock.h:47
 __traceiter_mmap_lock_acquire_returned+0x79/0xc0 include/trace/events/mmap_lock.h:47
 __do_trace_mmap_lock_acquire_returned include/trace/events/mmap_lock.h:47 [inline]
 trace_mmap_lock_acquire_returned include/trace/events/mmap_lock.h:47 [inline]
 __mmap_lock_do_trace_acquire_returned+0x138/0x1f0 mm/mmap_lock.c:35
 __mmap_lock_trace_acquire_returned include/linux/mmap_lock.h:36 [inline]
 mmap_read_trylock include/linux/mmap_lock.h:204 [inline]
 stack_map_get_build_id_offset+0x535/0x6f0 kernel/bpf/stackmap.c:157
 __bpf_get_stack+0x307/0xa10 kernel/bpf/stackmap.c:483
 ____bpf_get_stack kernel/bpf/stackmap.c:499 [inline]
 bpf_get_stack+0x32/0x40 kernel/bpf/stackmap.c:496
 ____bpf_get_stack_raw_tp kernel/trace/bpf_trace.c:1941 [inline]
 bpf_get_stack_raw_tp+0x124/0x160 kernel/trace/bpf_trace.c:1931
 bpf_prog_ec3b2eefa702d8d3+0x43/0x47

Tracepoint like trace_mmap_lock_acquire_returned may cause nested call
as the corner case show above, which will be resolved with more general
method in the future. As a result, WARN_ON_ONCE will be triggered. As
Alexei suggested, remove the WARN_ON_ONCE first.

Reported-by: syzbot+45b0c89a0fc7ae8dbadc@...kaller.appspotmail.com
Closes: https://lore.kernel.org/bpf/8bc2554d-1052-4922-8832-e0078a033e1d@gmail.com
Fixes: 9594dc3c7e71 ("bpf: fix nested bpf tracepoints with per-cpu data")
Suggested-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
---
 kernel/trace/bpf_trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Change list:
- v1 -> v2:
  - remove WARN() as Alexei suggested
  - rename the patch
- v1:
    https://lore.kernel.org/bpf/a3fa6129-933a-4747-8165-884e38c58e3b@linux.dev

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 187dc37d61..d14f0fdd7a 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1858,7 +1858,7 @@ static struct pt_regs *get_bpf_raw_tp_regs(void)
 	struct bpf_raw_tp_regs *tp_regs = this_cpu_ptr(&bpf_raw_tp_regs);
 	int nest_level = this_cpu_inc_return(bpf_raw_tp_nest_level);
 
-	if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(tp_regs->regs))) {
+	if (nest_level > ARRAY_SIZE(tp_regs->regs)) {
 		this_cpu_dec(bpf_raw_tp_nest_level);
 		return ERR_PTR(-EBUSY);
 	}
-- 
2.43.0