Linux kernel -stable discussions
 help / color / mirror / Atom feed
* FAILED: patch "[PATCH] ftrace: Fix BPF fexit with livepatch" failed to apply to 6.6-stable tree
@ 2025-11-20 16:17 gregkh
  2025-11-21 15:20 ` [PATCH 6.6.y] ftrace: Fix BPF fexit with livepatch Sasha Levin
  0 siblings, 1 reply; 2+ messages in thread
From: gregkh @ 2025-11-20 16:17 UTC (permalink / raw)
  To: song, andrey.grodzovsky, ast, jolsa, mhiramat, rostedt; +Cc: stable


The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 56b3c85e153b84f27e6cff39623ba40a1ad299d3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025112016-arrogance-recast-439f@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 56b3c85e153b84f27e6cff39623ba40a1ad299d3 Mon Sep 17 00:00:00 2001
From: Song Liu <song@kernel.org>
Date: Mon, 27 Oct 2025 10:50:21 -0700
Subject: [PATCH] ftrace: Fix BPF fexit with livepatch

When livepatch is attached to the same function as bpf trampoline with
a fexit program, bpf trampoline code calls register_ftrace_direct()
twice. The first time will fail with -EAGAIN, and the second time it
will succeed. This requires register_ftrace_direct() to unregister
the address on the first attempt. Otherwise, the bpf trampoline cannot
attach. Here is an easy way to reproduce this issue:

  insmod samples/livepatch/livepatch-sample.ko
  bpftrace -e 'fexit:cmdline_proc_show {}'
  ERROR: Unable to attach probe: fexit:vmlinux:cmdline_proc_show...

Fix this by cleaning up the hash when register_ftrace_function_nolock hits
errors.

Also, move the code that resets ops->func and ops->trampoline to the error
path of register_ftrace_direct(); and add a helper function reset_direct()
in register_ftrace_direct() and unregister_ftrace_direct().

Fixes: d05cb470663a ("ftrace: Fix modification of direct_function hash while in use")
Cc: stable@vger.kernel.org # v6.6+
Reported-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Closes: https://lore.kernel.org/live-patching/c5058315a39d4615b333e485893345be@crowdstrike.com/
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-and-tested-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: Song Liu <song@kernel.org>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251027175023.1521602-2-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 5949095e51c3..f2cb0b097093 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -479,11 +479,6 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 		 * BPF_TRAMP_F_SHARE_IPMODIFY is set, we can generate the
 		 * trampoline again, and retry register.
 		 */
-		/* reset fops->func and fops->trampoline for re-register */
-		tr->fops->func = NULL;
-		tr->fops->trampoline = 0;
-
-		/* free im memory and reallocate later */
 		bpf_tramp_image_free(im);
 		goto again;
 	}
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 42bd2ba68a82..cbeb7e833131 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5953,6 +5953,17 @@ static void register_ftrace_direct_cb(struct rcu_head *rhp)
 	free_ftrace_hash(fhp);
 }
 
+static void reset_direct(struct ftrace_ops *ops, unsigned long addr)
+{
+	struct ftrace_hash *hash = ops->func_hash->filter_hash;
+
+	remove_direct_functions_hash(hash, addr);
+
+	/* cleanup for possible another register call */
+	ops->func = NULL;
+	ops->trampoline = 0;
+}
+
 /**
  * register_ftrace_direct - Call a custom trampoline directly
  * for multiple functions registered in @ops
@@ -6048,6 +6059,8 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
 	ops->direct_call = addr;
 
 	err = register_ftrace_function_nolock(ops);
+	if (err)
+		reset_direct(ops, addr);
 
  out_unlock:
 	mutex_unlock(&direct_mutex);
@@ -6080,7 +6093,6 @@ EXPORT_SYMBOL_GPL(register_ftrace_direct);
 int unregister_ftrace_direct(struct ftrace_ops *ops, unsigned long addr,
 			     bool free_filters)
 {
-	struct ftrace_hash *hash = ops->func_hash->filter_hash;
 	int err;
 
 	if (check_direct_multi(ops))
@@ -6090,13 +6102,9 @@ int unregister_ftrace_direct(struct ftrace_ops *ops, unsigned long addr,
 
 	mutex_lock(&direct_mutex);
 	err = unregister_ftrace_function(ops);
-	remove_direct_functions_hash(hash, addr);
+	reset_direct(ops, addr);
 	mutex_unlock(&direct_mutex);
 
-	/* cleanup for possible another register call */
-	ops->func = NULL;
-	ops->trampoline = 0;
-
 	if (free_filters)
 		ftrace_free_filter(ops);
 	return err;


^ permalink raw reply related	[flat|nested] 2+ messages in thread
end of thread, other threads:[~2025-11-21 15:20 UTC | newest]

Thread overview: 2+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-11-20 16:17 FAILED: patch "[PATCH] ftrace: Fix BPF fexit with livepatch" failed to apply to 6.6-stable tree gregkh
2025-11-21 15:20 ` [PATCH 6.6.y] ftrace: Fix BPF fexit with livepatch Sasha Levin

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox