[PATCH 3/6 RESEND] x86/microcode/amd: Potentially delete invalid pointer

[Jiasheng Jiang]

Directly use __list_del() to remove 'p->plist' might be unsafe,
as we can see from the __list_del_entry_valid() of 'lib/list_debug.c'
that p->plist->prev or p->plist->next may be the LIST_POISON,
or p->list is not a valid double list.
In that case, __list_del() will be corruption.
Therefore, we suggest that __list_del_entry_valid()
should be added in front of the __list_del() in free_cache.

Signed-off-by: Jiasheng Jiang <jiasheng@xxxxxxxxxxx>
---
 arch/x86/kernel/cpu/microcode/amd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 3d4a483..e589cff 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -626,6 +626,8 @@ static void free_cache(void)
 	struct ucode_patch *p, *tmp;
 
 	list_for_each_entry_safe(p, tmp, &microcode_cache, plist) {
+		if (!__list_del_entry_valid(&p->plist))
+			continue;
 		__list_del(p->plist.prev, p->plist.next);
 		kfree(p->data);
 		kfree(p);
-- 
2.7.4