From: Daniel Axtens <dja@xxxxxxxxxx> Subject: kasan: allow architectures to provide an outline readiness check Allow architectures to define a kasan_arch_is_ready() hook that bails out of any function that's about to touch the shadow unless the arch says that it is ready for the memory to be accessed. This is fairly uninvasive and should have a negligible performance penalty. This will only work in outline mode, so an arch must specify ARCH_DISABLE_KASAN_INLINE if it requires this. Link: https://lkml.kernel.org/r/20210624034050.511391-3-dja@xxxxxxxxxx Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Suggested-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx> Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx> Cc: Balbir Singh <bsingharora@xxxxxxxxx> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/kasan/common.c | 3 +++ mm/kasan/generic.c | 3 +++ mm/kasan/kasan.h | 6 ++++++ mm/kasan/shadow.c | 6 ++++++ 4 files changed, 18 insertions(+) --- a/mm/kasan/common.c~kasan-allow-architectures-to-provide-an-outline-readiness-check +++ a/mm/kasan/common.c @@ -331,6 +331,9 @@ static inline bool ____kasan_slab_free(s u8 tag; void *tagged_object; + if (!kasan_arch_is_ready()) + return false; + tag = get_tag(object); tagged_object = object; object = kasan_reset_tag(object); --- a/mm/kasan/generic.c~kasan-allow-architectures-to-provide-an-outline-readiness-check +++ a/mm/kasan/generic.c @@ -163,6 +163,9 @@ static __always_inline bool check_region size_t size, bool write, unsigned long ret_ip) { + if (!kasan_arch_is_ready()) + return true; + if (unlikely(size == 0)) return true; --- a/mm/kasan/kasan.h~kasan-allow-architectures-to-provide-an-outline-readiness-check +++ a/mm/kasan/kasan.h @@ -449,6 +449,12 @@ static inline void kasan_poison_last_gra #endif /* CONFIG_KASAN_GENERIC */ +#ifndef kasan_arch_is_ready +static inline bool kasan_arch_is_ready(void) { return true; } +#elif !defined(CONFIG_KASAN_GENERIC) || !defined(CONFIG_KASAN_OUTLINE) +#error kasan_arch_is_ready only works in KASAN generic outline mode! +#endif + /* * Exported functions for interfaces called from assembly or from generated * code. Declarations here to avoid warning about missing declarations. --- a/mm/kasan/shadow.c~kasan-allow-architectures-to-provide-an-outline-readiness-check +++ a/mm/kasan/shadow.c @@ -73,6 +73,9 @@ void kasan_poison(const void *addr, size { void *shadow_start, *shadow_end; + if (!kasan_arch_is_ready()) + return; + /* * Perform shadow offset calculation based on untagged address, as * some of the callers (e.g. kasan_poison_object_data) pass tagged @@ -99,6 +102,9 @@ EXPORT_SYMBOL(kasan_poison); #ifdef CONFIG_KASAN_GENERIC void kasan_poison_last_granule(const void *addr, size_t size) { + if (!kasan_arch_is_ready()) + return; + if (size & KASAN_GRANULE_MASK) { u8 *shadow = (u8 *)kasan_mem_to_shadow(addr + size); *shadow = size & KASAN_GRANULE_MASK; _
