From: Tao Chen <chen.dylane@linux.dev>
To: song@kernel.org, jolsa@kernel.org, ast@kernel.org,
daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev,
eddyz87@gmail.com, yonghong.song@linux.dev,
john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me,
haoluo@google.com
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
Tao Chen <chen.dylane@linux.dev>
Subject: [PATCH bpf-next] bpf: Add preempt_disable to protect get_perf_callchain
Date: Mon, 22 Sep 2025 15:53:33 +0800 [thread overview]
Message-ID: <20250922075333.1452803-1-chen.dylane@linux.dev> (raw)
As Alexei suggested, the return value from get_perf_callchain() may be
reused if another task preempts and requests the stack after BPF program
switched to migrate disable.
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Tao Chen <chen.dylane@linux.dev>
---
kernel/bpf/stackmap.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 2e182a3ac4c..07892320906 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -314,8 +314,10 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
if (max_depth > sysctl_perf_event_max_stack)
max_depth = sysctl_perf_event_max_stack;
+ preempt_disable();
trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
false, false);
+ preempt_enable();
if (unlikely(!trace))
/* couldn't fetch the stack trace */
@@ -443,9 +445,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
if (sysctl_perf_event_max_stack < max_depth)
max_depth = sysctl_perf_event_max_stack;
- if (may_fault)
- rcu_read_lock(); /* need RCU for perf's callchain below */
-
+ preempt_disable();
if (trace_in)
trace = trace_in;
else if (kernel && task)
@@ -455,8 +455,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
crosstask, false);
if (unlikely(!trace) || trace->nr < skip) {
- if (may_fault)
- rcu_read_unlock();
+ preempt_enable();
goto err_fault;
}
@@ -474,10 +473,7 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
} else {
memcpy(buf, ips, copy_len);
}
-
- /* trace/ips should not be dereferenced after this point */
- if (may_fault)
- rcu_read_unlock();
+ preempt_enable();
if (user_build_id)
stack_map_get_build_id_offset(buf, trace_nr, user, may_fault);
--
2.48.1
next reply other threads:[~2025-09-22 7:54 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-22 7:53 Tao Chen [this message]
2025-09-23 2:53 ` [PATCH bpf-next] bpf: Add preempt_disable to protect get_perf_callchain Alexei Starovoitov
2025-09-25 17:45 ` Tao Chen
2025-09-25 23:03 ` Andrii Nakryiko
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