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ftrace: bpf: Fix IPMODIFY + DIRECT in modify_ftrace_direct()

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ftrace_hash_ipmodify_enable() checks IPMODIFY and DIRECT ftrace_ops on
the same kernel function. When needed, ftrace_hash_ipmodify_enable()
calls ops->ops_func() to prepare the direct ftrace (BPF trampoline) to
share the same function as the IPMODIFY ftrace (livepatch).

ftrace_hash_ipmodify_enable() is called in register_ftrace_direct() path,
but not called in modify_ftrace_direct() path. As a result, the following
operations will break livepatch:

1. Load livepatch to a kernel function;
2. Attach fentry program to the kernel function;
3. Attach fexit program to the kernel function.

After 3, the kernel function being used will not be the livepatched
version, but the original version.

Fix this by adding __ftrace_hash_update_ipmodify() to
__modify_ftrace_direct() and adjust some logic around the call.

Signed-off-by: Song Liu <song@kernel.org>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251027175023.1521602-3-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 10:50:22 -07:00
committed by Alexei Starovoitov
parent 56b3c85e15
commit 3e9a18e1c3
1 changed files with 31 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
kernel/trace/ftrace.c
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@@ -1971,7 +1971,8 @@ static void ftrace_hash_rec_enable_modify(struct ftrace_ops *ops)
*/
static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
struct ftrace_hash *old_hash,
struct ftrace_hash *new_hash)
struct ftrace_hash *new_hash,
bool update_target)
{
struct ftrace_page *pg;
struct dyn_ftrace *rec, *end = NULL;
@@ -2006,10 +2007,13 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
if (rec->flags & FTRACE_FL_DISABLED)
continue;
/* We need to update only differences of filter_hash */
/*
* Unless we are updating the target of a direct function,
* we only need to update differences of filter_hash
*/
in_old = !!ftrace_lookup_ip(old_hash, rec->ip);
in_new = !!ftrace_lookup_ip(new_hash, rec->ip);
if (in_old == in_new)
if (!update_target && (in_old == in_new))
continue;
if (in_new) {
@@ -2020,7 +2024,16 @@ static int __ftrace_hash_update_ipmodify(struct ftrace_ops *ops,
if (is_ipmodify)
goto rollback;
FTRACE_WARN_ON(rec->flags & FTRACE_FL_DIRECT);
/*
* If this is called by __modify_ftrace_direct()
* then it is only changing where the direct
* pointer is jumping to, and the record already
* points to a direct trampoline. If it isn't,
* then it is a bug to update ipmodify on a direct
* caller.
*/
FTRACE_WARN_ON(!update_target &&
(rec->flags & FTRACE_FL_DIRECT));
/*
* Another ops with IPMODIFY is already
@@ -2076,7 +2089,7 @@ static int ftrace_hash_ipmodify_enable(struct ftrace_ops *ops)
if (ftrace_hash_empty(hash))
hash = NULL;
return __ftrace_hash_update_ipmodify(ops, EMPTY_HASH, hash);
return __ftrace_hash_update_ipmodify(ops, EMPTY_HASH, hash, false);
}
/* Disabling always succeeds */
@@ -2087,7 +2100,7 @@ static void ftrace_hash_ipmodify_disable(struct ftrace_ops *ops)
if (ftrace_hash_empty(hash))
hash = NULL;
__ftrace_hash_update_ipmodify(ops, hash, EMPTY_HASH);
__ftrace_hash_update_ipmodify(ops, hash, EMPTY_HASH, false);
}
static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
@@ -2101,7 +2114,7 @@ static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
if (ftrace_hash_empty(new_hash))
new_hash = NULL;
return __ftrace_hash_update_ipmodify(ops, old_hash, new_hash);
return __ftrace_hash_update_ipmodify(ops, old_hash, new_hash, false);
}
static void print_ip_ins(const char *fmt, const unsigned char *p)
@@ -6114,7 +6127,7 @@ EXPORT_SYMBOL_GPL(unregister_ftrace_direct);
static int
__modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
{
struct ftrace_hash *hash;
struct ftrace_hash *hash = ops->func_hash->filter_hash;
struct ftrace_func_entry *entry, *iter;
static struct ftrace_ops tmp_ops = {
.func = ftrace_stub,
@@ -6134,13 +6147,21 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
if (err)
return err;
/*
* Call __ftrace_hash_update_ipmodify() here, so that we can call
* ops->ops_func for the ops. This is needed because the above
* register_ftrace_function_nolock() worked on tmp_ops.
*/
err = __ftrace_hash_update_ipmodify(ops, hash, hash, true);
if (err)
goto out;
/*
* Now the ftrace_ops_list_func() is called to do the direct callers.
* We can safely change the direct functions attached to each entry.
*/
mutex_lock(&ftrace_lock);
hash = ops->func_hash->filter_hash;
size = 1 << hash->size_bits;
for (i = 0; i < size; i++) {
hlist_for_each_entry(iter, &hash->buckets[i], hlist) {
@@ -6155,6 +6176,7 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
mutex_unlock(&ftrace_lock);
out:
/* Removing the tmp_ops will add the updated direct callers to the functions */
unregister_ftrace_function(&tmp_ops);