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FAILED: patch "[PATCH] ftrace: Fix BPF fexit with livepatch" failed to apply to 6.6-stable tree

PATCH New [email protected] 2 participants 2 messages Nov 20, 2025 – Nov 21, 2025

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Stable branch BPF Tracing BPF core +1 more subsystems
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#0 lore raw

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 <[email protected]>.

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 '<[email protected]>' --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 <[email protected]>
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 [email protected] # v6.6+
Reported-by Andrey Grodzovsky <[email protected]>
Closes https://lore.kernel.org/live-patching/[email protected]/ open here
Cc Steven Rostedt (Google) <[email protected]>
Cc Masami Hiramatsu (Google) <[email protected]>
Acked-and-tested-by Andrey Grodzovsky <[email protected]>
Signed-off-by Song Liu <[email protected]>
Reviewed-by Jiri Olsa <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Alexei Starovoitov <[email protected]>
Acked-by Steven Rostedt (Google) <[email protected]>
kernel/bpf/trampoline.c +0 -5
index 5949095e51c3..f2cb0b097093 100644
@@ -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;
 	}
kernel/trace/ftrace.c +14 -6
index 42bd2ba68a82..cbeb7e833131 100644
@@ -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;
maintainer
#1 lore raw

PATCH 1/1 ftrace: Fix BPF fexit with livepatch

From: Song Liu <[email protected]>

[ Upstream commit 56b3c85e153b84f27e6cff39623ba40a1ad299d3 ]

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 [email protected] # v6.6+
Reported-by Andrey Grodzovsky <[email protected]>
Closes https://lore.kernel.org/live-patching/[email protected]/ open here
Cc Steven Rostedt (Google) <[email protected]>
Cc Masami Hiramatsu (Google) <[email protected]>
Acked-and-tested-by Andrey Grodzovsky <[email protected]>
Signed-off-by Song Liu <[email protected]>
Reviewed-by Jiri Olsa <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
Signed-off-by Alexei Starovoitov <[email protected]>
Acked-by Steven Rostedt (Google) <[email protected]>
[ moved cleanup to reset_direct() ]
Signed-off-by Sasha Levin <[email protected]>
---
 kernel/bpf/trampoline.c |  4 ----
 kernel/trace/ftrace.c   | 20 ++++++++++++++------
 2 files changed, 14 insertions(+), 10 deletions(-)
kernel/bpf/trampoline.c +0 -4
index e97aeda3a86b5..b6024fc903490 100644
@@ -460,10 +460,6 @@ 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;
-
 		/* reset im->image memory attr for arch_prepare_bpf_trampoline */
 		set_memory_nx((long)im->image, 1);
 		set_memory_rw((long)im->image, 1);
kernel/trace/ftrace.c +14 -6
index 15785a729a0cd..ecda59d6acb4c 100644
@@ -5370,6 +5370,17 @@ static void remove_direct_functions_hash(struct ftrace_hash *hash, unsigned long
 	}
 }
 
+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

@@ -5465,6 +5476,8 @@ 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);

@@ -5497,7 +5510,6 @@ 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))

@@ -5507,13 +5519,9 @@ 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;
Signature · 1 line
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