From: Song Liu song@kernel.org
[ 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: 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 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 [ moved cleanup to reset_direct() ] Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/trampoline.c | 4 ---- kernel/trace/ftrace.c | 20 ++++++++++++++------ 2 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index e97aeda3a86b5..b6024fc903490 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -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); diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 15785a729a0cd..ecda59d6acb4c 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -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;