diff mbox series

[bpf-next,v2] bpf: Move out synchronize_rcu_tasks_trace from mutex CS

Message ID 20250104013946.1111785-1-pulehui@huaweicloud.com (mailing list archive)
State New
Delegated to: BPF
Headers show
Series [bpf-next,v2] bpf: Move out synchronize_rcu_tasks_trace from mutex CS | expand

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netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1 this patch: 1
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers warning 5 maintainers not CCed: mathieu.desnoyers@efficios.com mattbobrowski@google.com mhiramat@kernel.org linux-trace-kernel@vger.kernel.org rostedt@goodmis.org
netdev/build_clang success Errors and warnings before: 17 this patch: 17
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netdev/deprecated_api success None detected
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netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 19 this patch: 19
netdev/checkpatch warning WARNING: line length of 84 exceeds 80 columns WARNING: line length of 86 exceeds 80 columns WARNING: use of RCU tasks trace is incorrect outside BPF or core RCU code
netdev/build_clang_rust success No Rust files in patch. Skipping build
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netdev/source_inline success Was 0 now: 0

Commit Message

Pu Lehui Jan. 4, 2025, 1:39 a.m. UTC 
From: Pu Lehui <pulehui@huawei.com>

Commit ef1b808e3b7c ("bpf: Fix UAF via mismatching bpf_prog/attachment
RCU flavors") resolved a possible UAF issue in uprobes that attach
non-sleepable bpf prog by explicitly waiting for a tasks-trace-RCU grace
period. But, in the current implementation, synchronize_rcu_tasks_trace
is included within the mutex critical section, which increases the
length of the critical section and may affect performance. So let's move
out synchronize_rcu_tasks_trace from mutex CS.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
---
v2: Simplify code logic. (Jiri)

 kernel/trace/bpf_trace.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)
diff mbox series

Patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 48db147c6c7d..a90880f475af 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2245,6 +2245,7 @@  void perf_event_detach_bpf_prog(struct perf_event *event)
 {
 	struct bpf_prog_array *old_array;
 	struct bpf_prog_array *new_array;
+	struct bpf_prog *prog = NULL;
 	int ret;
 
 	mutex_lock(&bpf_event_mutex);
@@ -2265,18 +2266,22 @@  void perf_event_detach_bpf_prog(struct perf_event *event)
 	}
 
 put:
-	/*
-	 * It could be that the bpf_prog is not sleepable (and will be freed
-	 * via normal RCU), but is called from a point that supports sleepable
-	 * programs and uses tasks-trace-RCU.
-	 */
-	synchronize_rcu_tasks_trace();
-
-	bpf_prog_put(event->prog);
+	prog = event->prog;
 	event->prog = NULL;
 
 unlock:
 	mutex_unlock(&bpf_event_mutex);
+
+	if (prog) {
+		/*
+		 * It could be that the bpf_prog is not sleepable (and will be freed
+		 * via normal RCU), but is called from a point that supports sleepable
+		 * programs and uses tasks-trace-RCU.
+		 */
+		synchronize_rcu_tasks_trace();
+
+		bpf_prog_put(prog);
+	}
 }
 
 int perf_event_query_prog_array(struct perf_event *event, void __user *info)