Patch "fprobe: Release rethook after the ftrace_ops is unregistered" has been added to the 6.4-stable tree

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This is a note to let you know that I've just added the patch titled

    fprobe: Release rethook after the ftrace_ops is unregistered

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fprobe-release-rethook-after-the-ftrace_ops-is-unregistered.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 5f81018753dfd4989e33ece1f0cb6b8aae498b82 Mon Sep 17 00:00:00 2001
From: Jiri Olsa <jolsa@xxxxxxxxxx>
Date: Thu, 15 Jun 2023 13:52:36 +0200
Subject: fprobe: Release rethook after the ftrace_ops is unregistered

From: Jiri Olsa <jolsa@xxxxxxxxxx>

commit 5f81018753dfd4989e33ece1f0cb6b8aae498b82 upstream.

While running bpf selftests it's possible to get following fault:

  general protection fault, probably for non-canonical address \
  0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI
  ...
  Call Trace:
   <TASK>
   fprobe_handler+0xc1/0x270
   ? __pfx_bpf_testmod_init+0x10/0x10
   ? __pfx_bpf_testmod_init+0x10/0x10
   ? bpf_fentry_test1+0x5/0x10
   ? bpf_fentry_test1+0x5/0x10
   ? bpf_testmod_init+0x22/0x80
   ? do_one_initcall+0x63/0x2e0
   ? rcu_is_watching+0xd/0x40
   ? kmalloc_trace+0xaf/0xc0
   ? do_init_module+0x60/0x250
   ? __do_sys_finit_module+0xac/0x120
   ? do_syscall_64+0x37/0x90
   ? entry_SYSCALL_64_after_hwframe+0x72/0xdc
   </TASK>

In unregister_fprobe function we can't release fp->rethook while it's
possible there are some of its users still running on another cpu.

Moving rethook_free call after fp->ops is unregistered with
unregister_ftrace_function call.

Link: https://lore.kernel.org/all/20230615115236.3476617-1-jolsa@xxxxxxxxxx/

Fixes: 5b0ab78998e3 ("fprobe: Add exit_handler support")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/trace/fprobe.c |   12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -366,19 +366,13 @@ int unregister_fprobe(struct fprobe *fp)
 		    fp->ops.saved_func != fprobe_kprobe_handler))
 		return -EINVAL;
 
-	/*
-	 * rethook_free() starts disabling the rethook, but the rethook handlers
-	 * may be running on other processors at this point. To make sure that all
-	 * current running handlers are finished, call unregister_ftrace_function()
-	 * after this.
-	 */
-	if (fp->rethook)
-		rethook_free(fp->rethook);
-
 	ret = unregister_ftrace_function(&fp->ops);
 	if (ret < 0)
 		return ret;
 
+	if (fp->rethook)
+		rethook_free(fp->rethook);
+
 	ftrace_free_filter(&fp->ops);
 
 	return ret;


Patches currently in stable-queue which might be from jolsa@xxxxxxxxxx are

queue-6.4/fprobe-release-rethook-after-the-ftrace_ops-is-unregistered.patch



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