[PATCH 6.12 019/567] livepatch: Match old_sympos 0 and 1 in klp_find_func()

Greg Kroah-Hartman
2026-01-06T17:15:17Z

From: Song Liu <song@kernel.org>

[ Upstream commit 139560e8b973402140cafeb68c656c1374bd4c20 ]

When there is only one function of the same name, old_sympos of 0 and 1
are logically identical. Match them in klp_find_func().

This is to avoid a corner case with different toolchain behavior.

In this specific issue, two versions of kpatch-build were used to
build livepatch for the same kernel. One assigns old_sympos == 0 for
unique local functions, the other assigns old_sympos == 1 for unique
local functions. Both versions work fine by themselves. (PS: This
behavior change was introduced in a downstream version of kpatch-build.
This change does not exist in upstream kpatch-build.)

However, during livepatch upgrade (with the replace flag set) from a
patch built with one version of kpatch-build to the same fix built with
the other version of kpatch-build, livepatching fails with errors like:

[ 14.218706] sysfs: cannot create duplicate filename 'xxx/somefunc,1'
...
[ 14.219466] Call Trace:
[ 14.219468] <TASK>
[ 14.219469] dump_stack_lvl+0x47/0x60
[ 14.219474] sysfs_warn_dup.cold+0x17/0x27
[ 14.219476] sysfs_create_dir_ns+0x95/0xb0
[ 14.219479] kobject_add_internal+0x9e/0x260
[ 14.219483] kobject_add+0x68/0x80
[ 14.219485] ? kstrdup+0x3c/0xa0
[ 14.219486] klp_enable_patch+0x320/0x830
[ 14.219488] patch_init+0x443/0x1000 [ccc_0_6]
[ 14.219491] ? 0xffffffffa05eb000
[ 14.219492] do_one_initcall+0x2e/0x190
[ 14.219494] do_init_module+0x67/0x270
[ 14.219496] init_module_from_file+0x75/0xa0
[ 14.219499] idempotent_init_module+0x15a/0x240
[ 14.219501] __x64_sys_finit_module+0x61/0xc0
[ 14.219503] do_syscall_64+0x5b/0x160
[ 14.219505] entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 14.219507] RIP: 0033:0x7f545a4bd96d
...
[ 14.219516] kobject: kobject_add_internal failed for somefunc,1 with
-EEXIST, don't try to register things with the same name ...

This happens because klp_find_func() thinks somefunc with old_sympos==0
is not the same as somefunc with old_sympos==1, and klp_add_object_nops
adds another xxx/func,1 to the list of functions to patch.

Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
[pmladek@suse.com: Fixed some typos.]
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/livepatch/core.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 3c21c31796db0..077e078032e05 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -90,8 +90,14 @@ static struct klp_func *klp_find_func(struct klp_object *obj,
struct klp_func *func;

klp_for_each_func(obj, func) {
+ /*
+ * Besides identical old_sympos, also consider old_sympos
+ * of 0 and 1 are identical.
+ */
if ((strcmp(old_func->old_name, func->old_name) == 0) &&
- (old_func->old_sympos == func->old_sympos)) {
+ ((old_func->old_sympos == func->old_sympos) ||
+ (old_func->old_sympos == 0 && func->old_sympos == 1) ||
+ (old_func->old_sympos == 1 && func->old_sympos == 0))) {
return func;
}
}
--
2.51.0