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| author | Stephen Brennan <stephen.s.brennan@oracle.com> | 2024-05-01 18:29:56 +0200 |
|---|---|---|
| committer | Masami Hiramatsu (Google) <mhiramat@kernel.org> | 2024-05-16 00:23:30 +0200 |
| commit | 1a7d0890dd4a502a202aaec792a6c04e6e049547 (patch) | |
| tree | 1ef5c1732237654fddc49948aa9644070f82fcf9 /arch/powerpc | |
| parent | selftests/ftrace: Fix required features for VFS type test case (diff) | |
| download | linux-1a7d0890dd4a502a202aaec792a6c04e6e049547.tar.xz linux-1a7d0890dd4a502a202aaec792a6c04e6e049547.zip | |
kprobe/ftrace: bail out if ftrace was killed
If an error happens in ftrace, ftrace_kill() will prevent disarming
kprobes. Eventually, the ftrace_ops associated with the kprobes will be
freed, yet the kprobes will still be active, and when triggered, they
will use the freed memory, likely resulting in a page fault and panic.
This behavior can be reproduced quite easily, by creating a kprobe and
then triggering a ftrace_kill(). For simplicity, we can simulate an
ftrace error with a kernel module like [1]:
[1]: https://github.com/brenns10/kernel_stuff/tree/master/ftrace_killer
sudo perf probe --add commit_creds
sudo perf trace -e probe:commit_creds
# In another terminal
make
sudo insmod ftrace_killer.ko # calls ftrace_kill(), simulating bug
# Back to perf terminal
# ctrl-c
sudo perf probe --del commit_creds
After a short period, a page fault and panic would occur as the kprobe
continues to execute and uses the freed ftrace_ops. While ftrace_kill()
is supposed to be used only in extreme circumstances, it is invoked in
FTRACE_WARN_ON() and so there are many places where an unexpected bug
could be triggered, yet the system may continue operating, possibly
without the administrator noticing. If ftrace_kill() does not panic the
system, then we should do everything we can to continue operating,
rather than leave a ticking time bomb.
Link: https://lore.kernel.org/all/20240501162956.229427-1-stephen.s.brennan@oracle.com/
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Diffstat (limited to 'arch/powerpc')
| -rw-r--r-- | arch/powerpc/kernel/kprobes-ftrace.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c index 072ebe7f290b..f8208c027148 100644 --- a/arch/powerpc/kernel/kprobes-ftrace.c +++ b/arch/powerpc/kernel/kprobes-ftrace.c @@ -21,6 +21,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, struct pt_regs *regs; int bit; + if (unlikely(kprobe_ftrace_disabled)) + return; + bit = ftrace_test_recursion_trylock(nip, parent_nip); if (bit < 0) return; |