From 2597c9947b0174fcc71bdd7ab6cb49c2b4291e95 Mon Sep 17 00:00:00 2001 From: Benjamin Gray Date: Tue, 13 Feb 2024 14:39:58 +1100 Subject: kasan: guard release_free_meta() shadow access with kasan_arch_is_ready() release_free_meta() accesses the shadow directly through the path kasan_slab_free __kasan_slab_free kasan_release_object_meta release_free_meta kasan_mem_to_shadow There are no kasan_arch_is_ready() guards here, allowing an oops when the shadow is not initialized. The oops can be seen on a Power8 KVM guest. This patch adds the guard to release_free_meta(), as it's the first level that specifically requires the shadow. It is safe to put the guard at the start of this function, before the stack put: only kasan_save_free_info() can initialize the saved stack, which itself is guarded with kasan_arch_is_ready() by its caller poison_slab_object(). If the arch becomes ready before release_free_meta() then we will not observe KASAN_SLAB_FREE_META in the object's shadow, so we will not put an uninitialized stack either. Link: https://lkml.kernel.org/r/20240213033958.139383-1-bgray@linux.ibm.com Fixes: 63b85ac56a64 ("kasan: stop leaking stack trace handles") Signed-off-by: Benjamin Gray Reviewed-by: Andrey Konovalov Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Michael Ellerman Cc: Vincenzo Frascino Signed-off-by: Andrew Morton --- mm/kasan/generic.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'mm/kasan') diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c index df6627f62402..032bf3e98c24 100644 --- a/mm/kasan/generic.c +++ b/mm/kasan/generic.c @@ -522,6 +522,9 @@ static void release_alloc_meta(struct kasan_alloc_meta *meta) static void release_free_meta(const void *object, struct kasan_free_meta *meta) { + if (!kasan_arch_is_ready()) + return; + /* Check if free meta is valid. */ if (*(u8 *)kasan_mem_to_shadow(object) != KASAN_SLAB_FREE_META) return; -- cgit v1.2.3