From: Luo Gengkun <luogengkun@huaweicloud.com>
Date: Tue, 19 Aug 2025 10:51:52 +0000 (+0000)
Subject: tracing: Fix tracing_marker may trigger page fault during preempt_disable
X-Git-Tag: v6.12.48~116
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=3f9b5dfbc444cb7a8ce68254b348eed6d73c5bde;p=thirdparty%2Fkernel%2Fstable.git

tracing: Fix tracing_marker may trigger page fault during preempt_disable

[ Upstream commit 3d62ab32df065e4a7797204a918f6489ddb8a237 ]

Both tracing_mark_write and tracing_mark_raw_write call
__copy_from_user_inatomic during preempt_disable. But in some case,
__copy_from_user_inatomic may trigger page fault, and will call schedule()
subtly. And if a task is migrated to other cpu, the following warning will
be trigger:
        if (RB_WARN_ON(cpu_buffer,
                       !local_read(&cpu_buffer->committing)))

An example can illustrate this issue:

process flow						CPU
---------------------------------------------------------------------

tracing_mark_raw_write():				cpu:0
   ...
   ring_buffer_lock_reserve():				cpu:0
      ...
      cpu = raw_smp_processor_id()			cpu:0
      cpu_buffer = buffer->buffers[cpu]			cpu:0
      ...
   ...
   __copy_from_user_inatomic():				cpu:0
      ...
      # page fault
      do_mem_abort():					cpu:0
         ...
         # Call schedule
         schedule()					cpu:0
	 ...
   # the task schedule to cpu1
   __buffer_unlock_commit():				cpu:1
      ...
      ring_buffer_unlock_commit():			cpu:1
	 ...
	 cpu = raw_smp_processor_id()			cpu:1
	 cpu_buffer = buffer->buffers[cpu]		cpu:1

As shown above, the process will acquire cpuid twice and the return values
are not the same.

To fix this problem using copy_from_user_nofault instead of
__copy_from_user_inatomic, as the former performs 'access_ok' before
copying.

Link: https://lore.kernel.org/20250819105152.2766363-1-luogengkun@huaweicloud.com
Fixes: 656c7f0d2d2b ("tracing: Replace kmap with copy_from_user() in trace_marker writing")
Signed-off-by: Luo Gengkun <luogengkun@huaweicloud.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ba3358eef34ba..87a43c0f90764 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6949,7 +6949,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
 	entry = ring_buffer_event_data(event);
 	entry->ip = _THIS_IP_;
 
-	len = __copy_from_user_inatomic(&entry->buf, ubuf, cnt);
+	len = copy_from_user_nofault(&entry->buf, ubuf, cnt);
 	if (len) {
 		memcpy(&entry->buf, FAULTED_STR, FAULTED_SIZE);
 		cnt = FAULTED_SIZE;
@@ -7020,7 +7020,7 @@ tracing_mark_raw_write(struct file *filp, const char __user *ubuf,
 
 	entry = ring_buffer_event_data(event);
 
-	len = __copy_from_user_inatomic(&entry->id, ubuf, cnt);
+	len = copy_from_user_nofault(&entry->id, ubuf, cnt);
 	if (len) {
 		entry->id = -1;
 		memcpy(&entry->buf, FAULTED_STR, FAULTED_SIZE);