On Sun, Oct 26, 2025 at 01:54:43PM -0700, Song Liu wrote:
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().
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@crowd... 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
kernel/bpf/trampoline.c | 5 ----- kernel/trace/ftrace.c | 6 ++++++ 2 files changed, 6 insertions(+), 5 deletions(-)
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 */diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 42bd2ba68a82..725c224fb4e6 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6048,6 +6048,12 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) ops->direct_call = addr; err = register_ftrace_function_nolock(ops);
- if (err) {
/* cleanup for possible another register call */ops->func = NULL;ops->trampoline = 0;
nit, we could cleanup also flags and direct_call just to be complete, but at the same time it does not seem to affect anything
jirka
remove_direct_functions_hash(hash, addr);- }
out_unlock: mutex_unlock(&direct_mutex); -- 2.47.3