linux-kernel - [PATCH bpf-next] bpf: Add preempt_disable to protect get_perf

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Message-ID: <20250922075333.1452803-1-chen.dylane@linux.dev>
Date: Mon, 22 Sep 2025 15:53:33 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: song@...nel.org,
	jolsa@...nel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Tao Chen <chen.dylane@...ux.dev>
Subject: [PATCH bpf-next] bpf: Add preempt_disable to protect get_perf_callchain

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@...nel.org>
Signed-off-by: Tao Chen <chen.dylane@...ux.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