From a064cb00d359bc464df6fd2ab6dfb8dc4b31e361 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Thu, 29 Apr 2021 22:59:49 -0700 Subject: kasan: initialize shadow to TAG_INVALID for SW_TAGS Currently, KASAN_SW_TAGS uses 0xFF as the default tag value for unallocated memory. The underlying idea is that since that memory hasn't been allocated yet, it's only supposed to be dereferenced through a pointer with the native 0xFF tag. While this is a good idea in terms on consistency, practically it doesn't bring any benefit. Since the 0xFF pointer tag is a match-all tag, it doesn't matter what tag the accessed memory has. No accesses through 0xFF-tagged pointers are considered buggy by KASAN. This patch changes the default tag value for unallocated memory to 0xFE, which is the tag KASAN uses for inaccessible memory. This doesn't affect accesses through 0xFF-tagged pointer to this memory, but this allows KASAN to detect wild and large out-of-bounds invalid memory accesses through otherwise-tagged pointers. This is a prepatory patch for the next one, which changes the tag-based KASAN modes to not poison the boot memory. Link: https://lkml.kernel.org/r/c8e93571c18b3528aac5eb33ade213bf133d10ad.1613692950.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Branislav Rankov Cc: Catalin Marinas Cc: Christoph Hellwig Cc: Dmitry Vyukov Cc: Evgenii Stepanov Cc: Kevin Brodsky Cc: Marco Elver Cc: Peter Collingbourne Cc: Vincenzo Frascino Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/kasan.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/kasan.h b/include/linux/kasan.h index d53ea3c047bc..9f5faefd1744 100644 --- a/include/linux/kasan.h +++ b/include/linux/kasan.h @@ -30,7 +30,8 @@ struct kunit_kasan_expectation { /* Software KASAN implementations use shadow memory. */ #ifdef CONFIG_KASAN_SW_TAGS -#define KASAN_SHADOW_INIT 0xFF +/* This matches KASAN_TAG_INVALID. */ +#define KASAN_SHADOW_INIT 0xFE #else #define KASAN_SHADOW_INIT 0 #endif -- cgit v1.2.3