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kasan: remove use after scope bugs detection.

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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.rhgbjhhis53hkgfn@wfg-t540p.sh.intel.com>

Link: http://lkml.kernel.org/r/20190111185842.13978-1-aryabinin@virtuozzo.com
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Will Deacon <will.deacon@arm.com>		[arm64]
Cc: Qian Cai <cai@lca.pw>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrey Ryabinin 2019-03-05 15:41:20 -08:00 committed by Linus Torvalds
parent 46612b751c
commit 7771bdbbfd
9 changed files with 0 additions and 73 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/arm64/include/asm/memory.h
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@ -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

1
lib/Kconfig.debug
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@ -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)

10
lib/Kconfig.kasan
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@ -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

24
lib/test_kasan.c
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@ -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();

19
mm/kasan/generic.c
View File

@ -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)
{

3
mm/kasan/generic_report.c
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@ -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";

3
mm/kasan/kasan.h
View File

@ -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);

5
scripts/Makefile.kasan
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@ -27,14 +27,9 @@ else
$(call cc-param,asan-globals=1) \
$(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
$(call cc-param,asan-stack=$(CONFIG_KASAN_STACK)) \
$(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

4
scripts/gcc-plugins/Kconfig
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@ -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