Use after scope bugs detector seems to be almost entirely useless for the linux kernel. It exists over two years, but I've seen only one valid bug so far [1]. And the bug was fixed before it has been reported. There were some other use-after-scope reports, but they were false-positives due to different reasons like incompatibility with structleak plugin.
This feature significantly increases stack usage, especially with GCC < 9 version, and causes a 32K stack overflow. It probably adds performance penalty too. Given all that, let's remove use-after-scope detector entirely. While preparing this patch I've noticed that we mistakenly enable use-after-scope detection for clang compiler regardless of CONFIG_KASAN_EXTRA setting. This is also fixed now. [1] http://lkml.kernel.org/r/<20171129052106.rhgbjhhis53hk...@wfg-t540p.sh.intel.com> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> Cc: Qian Cai <c...@lca.pw> Cc: Alexander Potapenko <gli...@google.com> Cc: Dmitry Vyukov <dvyu...@google.com> Cc: Catalin Marinas <catalin.mari...@arm.com> Cc: Will Deacon <will.dea...@arm.com> --- arch/arm64/include/asm/memory.h | 4 ---- lib/Kconfig.debug | 1 - lib/Kconfig.kasan | 10 ---------- lib/test_kasan.c | 24 ------------------------ mm/kasan/generic.c | 19 ------------------- mm/kasan/generic_report.c | 3 --- mm/kasan/kasan.h | 3 --- scripts/Makefile.kasan | 5 ----- scripts/gcc-plugins/Kconfig | 4 ---- 9 files changed, 73 deletions(-) diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index e1ec947e7c0c..0e236a99b3ef 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -80,11 +80,7 @@ */ #ifdef CONFIG_KASAN #define KASAN_SHADOW_SIZE (UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT)) -#ifdef CONFIG_KASAN_EXTRA -#define KASAN_THREAD_SHIFT 2 -#else #define KASAN_THREAD_SHIFT 1 -#endif /* CONFIG_KASAN_EXTRA */ #else #define KASAN_SHADOW_SIZE (0) #define KASAN_THREAD_SHIFT 0 diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index d4df5b24d75e..a219f3488ad7 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -222,7 +222,6 @@ config ENABLE_MUST_CHECK config FRAME_WARN int "Warn for stack frames larger than (needs gcc 4.4)" range 0 8192 - default 3072 if KASAN_EXTRA default 2048 if GCC_PLUGIN_LATENT_ENTROPY default 1280 if (!64BIT && PARISC) default 1024 if (!64BIT && !PARISC) diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan index d8c474b6691e..67d7d1309c52 100644 --- a/lib/Kconfig.kasan +++ b/lib/Kconfig.kasan @@ -78,16 +78,6 @@ config KASAN_SW_TAGS endchoice -config KASAN_EXTRA - bool "KASAN: extra checks" - depends on KASAN_GENERIC && DEBUG_KERNEL && !COMPILE_TEST - help - This enables further checks in generic KASAN, for now it only - includes the address-use-after-scope check that can lead to - excessive kernel stack usage, frame size warnings and longer - compile time. - See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 - choice prompt "Instrumentation type" depends on KASAN diff --git a/lib/test_kasan.c b/lib/test_kasan.c index 51b78405bf24..7de2702621dc 100644 --- a/lib/test_kasan.c +++ b/lib/test_kasan.c @@ -480,29 +480,6 @@ static noinline void __init copy_user_test(void) kfree(kmem); } -static noinline void __init use_after_scope_test(void) -{ - volatile char *volatile p; - - pr_info("use-after-scope on int\n"); - { - int local = 0; - - p = (char *)&local; - } - p[0] = 1; - p[3] = 1; - - pr_info("use-after-scope on array\n"); - { - char local[1024] = {0}; - - p = local; - } - p[0] = 1; - p[1023] = 1; -} - static noinline void __init kasan_alloca_oob_left(void) { volatile int i = 10; @@ -682,7 +659,6 @@ static int __init kmalloc_tests_init(void) kasan_alloca_oob_right(); ksize_unpoisons_memory(); copy_user_test(); - use_after_scope_test(); kmem_cache_double_free(); kmem_cache_invalid_free(); kasan_memchr(); diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c index ccb6207276e3..504c79363a34 100644 --- a/mm/kasan/generic.c +++ b/mm/kasan/generic.c @@ -275,25 +275,6 @@ EXPORT_SYMBOL(__asan_storeN_noabort); void __asan_handle_no_return(void) {} EXPORT_SYMBOL(__asan_handle_no_return); -/* Emitted by compiler to poison large objects when they go out of scope. */ -void __asan_poison_stack_memory(const void *addr, size_t size) -{ - /* - * Addr is KASAN_SHADOW_SCALE_SIZE-aligned and the object is surrounded - * by redzones, so we simply round up size to simplify logic. - */ - kasan_poison_shadow(addr, round_up(size, KASAN_SHADOW_SCALE_SIZE), - KASAN_USE_AFTER_SCOPE); -} -EXPORT_SYMBOL(__asan_poison_stack_memory); - -/* Emitted by compiler to unpoison large objects when they go into scope. */ -void __asan_unpoison_stack_memory(const void *addr, size_t size) -{ - kasan_unpoison_shadow(addr, 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) { diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c index 5e12035888f2..36c645939bc9 100644 --- a/mm/kasan/generic_report.c +++ b/mm/kasan/generic_report.c @@ -82,9 +82,6 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info) case KASAN_KMALLOC_FREE: bug_type = "use-after-free"; break; - 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"; diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h index ea51b2d898ec..3e0c11f7d7a1 100644 --- a/mm/kasan/kasan.h +++ b/mm/kasan/kasan.h @@ -34,7 +34,6 @@ #define KASAN_STACK_MID 0xF2 #define KASAN_STACK_RIGHT 0xF3 #define KASAN_STACK_PARTIAL 0xF4 -#define KASAN_USE_AFTER_SCOPE 0xF8 /* * alloca redzone shadow values @@ -187,8 +186,6 @@ void __asan_unregister_globals(struct kasan_global *globals, size_t size); void __asan_loadN(unsigned long addr, size_t size); void __asan_storeN(unsigned long addr, size_t size); void __asan_handle_no_return(void); -void __asan_poison_stack_memory(const void *addr, size_t size); -void __asan_unpoison_stack_memory(const void *addr, size_t size); void __asan_alloca_poison(unsigned long addr, size_t size); void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom); diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan index 25c259df8ffa..f1fb8e502657 100644 --- a/scripts/Makefile.kasan +++ b/scripts/Makefile.kasan @@ -27,14 +27,9 @@ else $(call cc-param,asan-globals=1) \ $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \ $(call cc-param,asan-stack=1) \ - $(call cc-param,asan-use-after-scope=1) \ $(call cc-param,asan-instrument-allocas=1) endif -ifdef CONFIG_KASAN_EXTRA -CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope) -endif - endif # CONFIG_KASAN_GENERIC ifdef CONFIG_KASAN_SW_TAGS diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig index d45f7f36b859..d9fd9988ef27 100644 --- a/scripts/gcc-plugins/Kconfig +++ b/scripts/gcc-plugins/Kconfig @@ -68,10 +68,6 @@ config GCC_PLUGIN_LATENT_ENTROPY config GCC_PLUGIN_STRUCTLEAK bool "Force initialization of variables containing userspace addresses" - # Currently STRUCTLEAK inserts initialization out of live scope of - # variables from KASAN point of view. This leads to KASAN false - # positive reports. Prohibit this combination for now. - depends on !KASAN_EXTRA help This plugin zero-initializes any structures containing a __user attribute. This can prevent some classes of information -- 2.19.2
