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ftrace: Fix BPF fexit with livepatch

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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>
This commit is contained in:
Song Liu 2025-10-27 10:50:21 -07:00 committed by Alexei Starovoitov
parent 6146a0f1df
commit 56b3c85e15
2 changed files with 14 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
kernel/bpf/trampoline.c
View File

@ -479,11 +479,6 @@ again:
* 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;
}

20
kernel/trace/ftrace.c
View File

@ -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;