On Thu, Nov 30, 2017 at 9:26 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > /\/\/\/\/\/\On Wed, Nov 29, 2017 at 10:50 PM, Paul Lawrence > <paullawrence@xxxxxxxxxx> wrote: >> clang's AddressSanitizer implementation adds redzones on either side of >> alloca()ed buffers. These redzones are 32-byte aligned and at least 32 >> bytes long. >> >> __asan_alloca_poison() is passed the size and address of the allocated >> buffer, *excluding* the redzones on either side. The left redzone will >> always be to the immediate left of this buffer; but AddressSanitizer may >> need to add padding between the end of the buffer and the right redzone. >> If there are any 8-byte chunks inside this padding, we should poison >> those too. >> >> __asan_allocas_unpoison() is just passed the top and bottom of the >> dynamic stack area, so unpoisoning is simpler. >> >> Signed-off-by: Greg Hackmann <ghackmann@xxxxxxxxxx> >> Signed-off-by: Paul Lawrence <paullawrence@xxxxxxxxxx> >> >> mm/kasan/kasan.c | 32 ++++++++++++++++++++++++++++++++ >> mm/kasan/kasan.h | 8 ++++++++ >> mm/kasan/report.c | 4 ++++ >> 3 files changed, 44 insertions(+) >> >> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c >> index 405bba487df5..f86f862f41f8 100644 >> --- a/mm/kasan/kasan.c >> +++ b/mm/kasan/kasan.c >> @@ -736,6 +736,38 @@ void __asan_unpoison_stack_memory(const void *addr, size_t size) >> } >> EXPORT_SYMBOL(__asan_unpoison_stack_memory); >> >> +/* Emitted by compiler to poison alloca()ed objects. */ >> +void __asan_alloca_poison(unsigned long addr, size_t size) >> +{ >> + size_t rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE); >> + size_t padding_size = round_up(size, KASAN_ALLOCA_REDZONE_SIZE) - >> + rounded_up_size; >> + >> + const void *left_redzone = (const void *)(addr - >> + KASAN_ALLOCA_REDZONE_SIZE); >> + const void *right_redzone = (const void *)(addr + rounded_up_size); >> + >> + WARN_ON(!IS_ALIGNED(addr, KASAN_ALLOCA_REDZONE_SIZE)); >> + >> + kasan_unpoison_shadow((const void *)addr, size); > > /\/\/\/\/\/\ > > Why do we need this? Stack must be clean. Compiler instrumentation > does not clear shadow for objects in function prologue, if stack is > dirty KASAN would explode. > > >> + kasan_poison_shadow(left_redzone, KASAN_ALLOCA_REDZONE_SIZE, >> + KASAN_ALLOCA_LEFT); >> + kasan_poison_shadow(right_redzone, >> + padding_size + KASAN_ALLOCA_REDZONE_SIZE, >> + KASAN_ALLOCA_RIGHT); > > We also need to poison [size, rounded_up_size) with partial value if > the range is not empty. I.e. we can poison exactly, say, 3 bytes > there. Wait, kasan_unpoison_shadow does this, right? Somewhat counter-intuitive and more expensive than needed. Let's poison only the last byte. >> +} >> +EXPORT_SYMBOL(__asan_alloca_poison); >> + >> +/* Emitted by compiler to unpoison alloca()ed areas when the stack unwinds. */ >> +void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom) >> +{ >> + if (unlikely(!stack_top || stack_top > stack_bottom)) >> + return; >> + >> + kasan_unpoison_shadow(stack_top, stack_bottom - stack_top); >> +} >> +EXPORT_SYMBOL(__asan_allocas_unpoison); >> + >> #ifdef CONFIG_MEMORY_HOTPLUG >> static int __meminit kasan_mem_notifier(struct notifier_block *nb, >> unsigned long action, void *data) >> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h >> index c70851a9a6a4..7c0bcd1f4c0d 100644 >> --- a/mm/kasan/kasan.h >> +++ b/mm/kasan/kasan.h >> @@ -24,6 +24,14 @@ >> #define KASAN_STACK_PARTIAL 0xF4 >> #define KASAN_USE_AFTER_SCOPE 0xF8 >> >> +/* >> + * alloca redzone shadow values >> + */ >> +#define KASAN_ALLOCA_LEFT 0xCA >> +#define KASAN_ALLOCA_RIGHT 0xCB >> + >> +#define KASAN_ALLOCA_REDZONE_SIZE 32 >> + >> /* Don't break randconfig/all*config builds */ >> #ifndef KASAN_ABI_VERSION >> #define KASAN_ABI_VERSION 1 >> diff --git a/mm/kasan/report.c b/mm/kasan/report.c >> index 6bcfb01ba038..25419d426426 100644 >> --- a/mm/kasan/report.c >> +++ b/mm/kasan/report.c >> @@ -102,6 +102,10 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info) >> case KASAN_USE_AFTER_SCOPE: >> bug_type = "use-after-scope"; >> break; >> + case KASAN_ALLOCA_LEFT: >> + case KASAN_ALLOCA_RIGHT: >> + bug_type = "alloca-out-of-bounds"; >> + break; >> } >> >> return bug_type; >> -- >> 2.15.0.531.g2ccb3012c9-goog >> -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html