Linux-ARM-Kernel Archive on lore.kernel.org
 help / Atom feed
* [PATCH] kasan: Remove use after scope bugs detection.
@ 2019-01-11 18:58 Andrey Ryabinin
  2019-01-14 13:24 ` Dmitry Vyukov
  2019-01-16 16:47 ` Will Deacon
  0 siblings, 2 replies; 4+ messages in thread
From: Andrey Ryabinin @ 2019-01-11 18:58 UTC (permalink / raw)
  To: akpm
  Cc: Catalin Marinas, Will Deacon, linux-kernel, kasan-dev, linux-mm,
	Qian Cai, Dmitry Vyukov, Andrey Ryabinin, Alexander Potapenko,
	linux-arm-kernel

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>

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
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>
Cc: Will Deacon <will.deacon@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


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] kasan: Remove use after scope bugs detection.
  2019-01-11 18:58 [PATCH] kasan: Remove use after scope bugs detection Andrey Ryabinin
@ 2019-01-14 13:24 ` Dmitry Vyukov
  2019-01-14 16:08   ` Andrey Ryabinin
  2019-01-16 16:47 ` Will Deacon
  1 sibling, 1 reply; 4+ messages in thread
From: Dmitry Vyukov @ 2019-01-14 13:24 UTC (permalink / raw)
  To: Andrey Ryabinin
  Cc: Catalin Marinas, Will Deacon, LKML, kasan-dev, Linux-MM,
	Qian Cai, Alexander Potapenko, Andrew Morton, Linux ARM

On Fri, Jan 11, 2019 at 7:58 PM Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
>
> 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.

Hi Andrey,

I am on a fence. On one hand removing bug detection sucks and each
case of a missed memory corruption leads to a splash of assorted bug
reports by syzbot. On the other hand everything you said is true.
Maybe support for CONFIG_VMAP_STACK will enable stacks larger then
PAGE_ALLOC_COSTLY_ORDER?




> [1] http://lkml.kernel.org/r/<20171129052106.rhgbjhhis53hkgfn@wfg-t540p.sh.intel.com>
>
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> 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>
> Cc: Will Deacon <will.deacon@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
>
> --
> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com.
> To post to this group, send email to kasan-dev@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20190111185842.13978-1-aryabinin%40virtuozzo.com.
> For more options, visit https://groups.google.com/d/optout.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] kasan: Remove use after scope bugs detection.
  2019-01-14 13:24 ` Dmitry Vyukov
@ 2019-01-14 16:08   ` Andrey Ryabinin
  0 siblings, 0 replies; 4+ messages in thread
From: Andrey Ryabinin @ 2019-01-14 16:08 UTC (permalink / raw)
  To: Dmitry Vyukov
  Cc: Catalin Marinas, Will Deacon, LKML, kasan-dev, Linux-MM,
	Qian Cai, Alexander Potapenko, Andrew Morton, Linux ARM

On 1/14/19 4:24 PM, Dmitry Vyukov wrote:
> On Fri, Jan 11, 2019 at 7:58 PM Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
>>
>> 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.
> 
> Hi Andrey,
> 
> I am on a fence. On one hand removing bug detection sucks and each
> case of a missed memory corruption leads to a splash of assorted bug
> reports by syzbot. On the other hand everything you said is true.
> Maybe support for CONFIG_VMAP_STACK will enable stacks larger then
> PAGE_ALLOC_COSTLY_ORDER?
> 

Yes, with vmap stacks higher order won't be a problem, since vmalloc() does only 0-order 
allocations. But even with vmap stacks use-after-scope won't become useful,
thus I don't see the point of re-enabling it with vmap stacks.
If feature doesn't detect bugs, but waste resources, than it's bad for detecting bugs.
We wasting our limited resources for useless checks, instead of using these resources
for doing more useful checks, running tests faster hence detecting more bugs per-time. 





_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH] kasan: Remove use after scope bugs detection.
  2019-01-11 18:58 [PATCH] kasan: Remove use after scope bugs detection Andrey Ryabinin
  2019-01-14 13:24 ` Dmitry Vyukov
@ 2019-01-16 16:47 ` Will Deacon
  1 sibling, 0 replies; 4+ messages in thread
From: Will Deacon @ 2019-01-16 16:47 UTC (permalink / raw)
  To: Andrey Ryabinin
  Cc: Catalin Marinas, linux-kernel, kasan-dev, linux-mm, Qian Cai,
	Dmitry Vyukov, Alexander Potapenko, akpm, linux-arm-kernel

On Fri, Jan 11, 2019 at 09:58:42PM +0300, Andrey Ryabinin wrote:
> 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>
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
> 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>
> Cc: Will Deacon <will.deacon@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(-)

For the arm64 part:

Acked-by: Will Deacon <will.deacon@arm.com>

but I defer to you and Dmitry as to whether or not you go ahead with this.

Will

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, back to index

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-01-11 18:58 [PATCH] kasan: Remove use after scope bugs detection Andrey Ryabinin
2019-01-14 13:24 ` Dmitry Vyukov
2019-01-14 16:08   ` Andrey Ryabinin
2019-01-16 16:47 ` Will Deacon

Linux-ARM-Kernel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-arm-kernel/0 linux-arm-kernel/git/0.git
	git clone --mirror https://lore.kernel.org/linux-arm-kernel/1 linux-arm-kernel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-arm-kernel linux-arm-kernel/ https://lore.kernel.org/linux-arm-kernel \
		linux-arm-kernel@lists.infradead.org infradead-linux-arm-kernel@archiver.kernel.org
	public-inbox-index linux-arm-kernel


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-arm-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox