[PATCH 5.4] ftrace: use preempt_enable/disable notrace macros to avoid double fault

[PATCH 5.4] ftrace: use preempt_enable/disable notrace macros to avoid double fault

[Koichiro Den]

Since the backport commit eea46baf1451 ("ftrace: Fix possible
use-after-free issue in ftrace_location()") on linux-5.4.y branch, the
old ftrace_int3_handler()->ftrace_location() path has included
rcu_read_lock(), which has mcount location inside and leads to potential
double fault.

Replace rcu_read_lock/unlock with preempt_enable/disable notrace macros
so that the mcount location does not appear on the int3 handler path.

This fix is specific to linux-5.4.y branch, the only branch still using
ftrace_int3_handler with commit e60b613df8b6 ("ftrace: Fix possible
use-after-free issue in ftrace_location()") backported. It also avoids
the need to backport the code conversion to text_poke() on this branch.

Reported-by: Koichiro Den <koichiro.den@canonical.com>
Closes: https://lore.kernel.org/all/74gjhwxupvozwop7ndhrh7t5qeckomt7yqvkkbm5j2tlx6dkfk@rgv7sijvry2k
Fixes: eea46baf1451 ("ftrace: Fix possible use-after-free issue in ftrace_location()") # linux-5.4.y
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
---
 kernel/trace/ftrace.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 380032a27f98..2eb1a8ec5755 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1554,7 +1554,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 	struct dyn_ftrace key;
 	unsigned long ip = 0;
 
-	rcu_read_lock();
+	preempt_disable_notrace();
 	key.ip = start;
 	key.flags = end;	/* overload flags, as it is unsigned long */
 
@@ -1572,7 +1572,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 			break;
 		}
 	}
-	rcu_read_unlock();
+	preempt_enable_notrace();
 	return ip;
 }
 
-- 
2.43.0

Re: [PATCH 5.4] ftrace: use preempt_enable/disable notrace macros to avoid double fault

[kernel test robot]

Hi,

Thanks for your patch.

FYI: kernel test robot notices the stable kernel rule is not satisfied.

The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html#option-3

Rule: The upstream commit ID must be specified with a separate line above the commit text.
Subject: [PATCH 5.4] ftrace: use preempt_enable/disable notrace macros to avoid double fault
Link: https://lore.kernel.org/stable/20250108031736.3318120-1-koichiro.den%40canonical.com

Please ignore this mail if the patch is not relevant for upstream.

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 5.4] ftrace: use preempt_enable/disable notrace macros to avoid double fault

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

No upstream commit was identified. Using temporary commit for testing.

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.4.y        |  Success    |  Success   |

Re: [PATCH 5.4] ftrace: use preempt_enable/disable notrace macros to avoid double fault

[Greg KH]

On Wed, Jan 08, 2025 at 12:17:36PM +0900, Koichiro Den wrote:
> Since the backport commit eea46baf1451 ("ftrace: Fix possible
> use-after-free issue in ftrace_location()") on linux-5.4.y branch, the
> old ftrace_int3_handler()->ftrace_location() path has included
> rcu_read_lock(), which has mcount location inside and leads to potential
> double fault.
> 
> Replace rcu_read_lock/unlock with preempt_enable/disable notrace macros
> so that the mcount location does not appear on the int3 handler path.
> 
> This fix is specific to linux-5.4.y branch, the only branch still using
> ftrace_int3_handler with commit e60b613df8b6 ("ftrace: Fix possible
> use-after-free issue in ftrace_location()") backported. It also avoids
> the need to backport the code conversion to text_poke() on this branch.
> 
> Reported-by: Koichiro Den <koichiro.den@canonical.com>
> Closes: https://lore.kernel.org/all/74gjhwxupvozwop7ndhrh7t5qeckomt7yqvkkbm5j2tlx6dkfk@rgv7sijvry2k
> Fixes: eea46baf1451 ("ftrace: Fix possible use-after-free issue in ftrace_location()") # linux-5.4.y
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
> ---
>  kernel/trace/ftrace.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Thanks, now queued up.

greg k-h