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Date:   Thu, 7 Jan 2021 14:00:45 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Walter Wu <walter-zh.wu@...iatek.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        wsd_upstream <wsd_upstream@...iatek.com>,
        linux-mediatek@...ts.infradead.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] kasan: remove redundant config option

On Thu, Jan 07, 2021 at 02:21:52PM +0800, Walter Wu wrote:
> CONFIG_KASAN_STACK and CONFIG_KASAN_STACK_ENABLE both enable KASAN
> stack instrumentation, but we should only need one config option,
> so that we remove CONFIG_KASAN_STACK_ENABLE. see [1].
> 
> For gcc we could do no prompt and default value y, and for clang
> prompt and default value n.
> 
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=210221
> 
> Signed-off-by: Walter Wu <walter-zh.wu@...iatek.com>
> Suggested-by: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Andrey Konovalov <andreyknvl@...gle.com>
> Cc: Alexander Potapenko <glider@...gle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
>  arch/arm64/kernel/sleep.S        |  2 +-
>  arch/x86/kernel/acpi/wakeup_64.S |  2 +-
>  include/linux/kasan.h            |  2 +-
>  lib/Kconfig.kasan                | 11 ++++-------
>  mm/kasan/common.c                |  2 +-
>  mm/kasan/kasan.h                 |  2 +-
>  mm/kasan/report_generic.c        |  2 +-
>  scripts/Makefile.kasan           | 10 ++++++++--
>  8 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> index 6bdef7362c0e..7c44ede122a9 100644
> --- a/arch/arm64/kernel/sleep.S
> +++ b/arch/arm64/kernel/sleep.S
> @@ -133,7 +133,7 @@ SYM_FUNC_START(_cpu_resume)
>  	 */
>  	bl	cpu_do_resume
>  
> -#if defined(CONFIG_KASAN) && CONFIG_KASAN_STACK
> +#if defined(CONFIG_KASAN) && defined(CONFIG_KASAN_STACK)
>  	mov	x0, sp
>  	bl	kasan_unpoison_task_stack_below
>  #endif
> diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
> index 5d3a0b8fd379..c7f412f4e07d 100644
> --- a/arch/x86/kernel/acpi/wakeup_64.S
> +++ b/arch/x86/kernel/acpi/wakeup_64.S
> @@ -112,7 +112,7 @@ SYM_FUNC_START(do_suspend_lowlevel)
>  	movq	pt_regs_r14(%rax), %r14
>  	movq	pt_regs_r15(%rax), %r15
>  
> -#if defined(CONFIG_KASAN) && CONFIG_KASAN_STACK
> +#if defined(CONFIG_KASAN) && defined(CONFIG_KASAN_STACK)
>  	/*
>  	 * The suspend path may have poisoned some areas deeper in the stack,
>  	 * which we now need to unpoison.
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 5e0655fb2a6f..35d1e9b2cbfa 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -302,7 +302,7 @@ static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
>  
>  #endif /* CONFIG_KASAN */
>  
> -#if defined(CONFIG_KASAN) && CONFIG_KASAN_STACK
> +#if defined(CONFIG_KASAN) && defined(CONFIG_KASAN_STACK)
>  void kasan_unpoison_task_stack(struct task_struct *task);
>  #else
>  static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index f5fa4ba126bf..59de74293454 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -138,9 +138,11 @@ config KASAN_INLINE
>  
>  endchoice
>  
> -config KASAN_STACK_ENABLE
> -	bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST

You are effectively undoing commits 6baec880d7a5 ("kasan: turn off
asan-stack for clang-8 and earlier") and ebb6d35a74ce ("kasan: remove
clang version check for KASAN_STACK") with this change. This change
should still remain around so that all{mod,yes}config remain mostly
clean for clang builds. This should not change anything from the user's
perspective because this option was never user selectable for GCC and
the default y keeps it on.

> +config KASAN_STACK
> +	bool "Enable stack instrumentation (unsafe)"
>  	depends on KASAN_GENERIC || KASAN_SW_TAGS
> +	default y if CC_IS_GCC
> +	default n if CC_IS_CLANG

This is implied and can be removed.

>  	help
>  	  The LLVM stack address sanitizer has a know problem that
>  	  causes excessive stack usage in a lot of functions, see
> @@ -154,11 +156,6 @@ config KASAN_STACK_ENABLE
>  	  CONFIG_COMPILE_TEST.	On gcc it is assumed to always be safe
>  	  to use and enabled by default.
>  
> -config KASAN_STACK
> -	int
> -	default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
> -	default 0
> -
>  config KASAN_SW_TAGS_IDENTIFY
>  	bool "Enable memory corruption identification"
>  	depends on KASAN_SW_TAGS
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 38ba2aecd8f4..02ec7f81dc16 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -63,7 +63,7 @@ void __kasan_unpoison_range(const void *address, size_t size)
>  	unpoison_range(address, size);
>  }
>  
> -#if CONFIG_KASAN_STACK
> +#if defined(CONFIG_KASAN_STACK)

Isn't '#ifdef CONFIG_...' preferred for CONFIG symbols?

>  /* Unpoison the entire stack for a task. */
>  void kasan_unpoison_task_stack(struct task_struct *task)
>  {
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index cc4d9e1d49b1..bdfdb1cff653 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -224,7 +224,7 @@ void *find_first_bad_addr(void *addr, size_t size);
>  const char *get_bug_type(struct kasan_access_info *info);
>  void metadata_fetch_row(char *buffer, void *row);
>  
> -#if defined(CONFIG_KASAN_GENERIC) && CONFIG_KASAN_STACK
> +#if defined(CONFIG_KASAN_GENERIC) && defined(CONFIG_KASAN_STACK)
>  void print_address_stack_frame(const void *addr);
>  #else
>  static inline void print_address_stack_frame(const void *addr) { }
> diff --git a/mm/kasan/report_generic.c b/mm/kasan/report_generic.c
> index 8a9c889872da..137a1dba1978 100644
> --- a/mm/kasan/report_generic.c
> +++ b/mm/kasan/report_generic.c
> @@ -128,7 +128,7 @@ void metadata_fetch_row(char *buffer, void *row)
>  	memcpy(buffer, kasan_mem_to_shadow(row), META_BYTES_PER_ROW);
>  }
>  
> -#if CONFIG_KASAN_STACK
> +#if defined(CONFIG_KASAN_STACK)
>  static bool __must_check tokenize_frame_descr(const char **frame_descr,
>  					      char *token, size_t max_tok_len,
>  					      unsigned long *value)
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index 1e000cc2e7b4..abf231d209b1 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -2,6 +2,12 @@
>  CFLAGS_KASAN_NOSANITIZE := -fno-builtin
>  KASAN_SHADOW_OFFSET ?= $(CONFIG_KASAN_SHADOW_OFFSET)
>  
> +ifdef CONFIG_KASAN_STACK
> +	stack_enable := 1
> +else
> +	stack_enable := 0
> +endif
> +
>  ifdef CONFIG_KASAN_GENERIC
>  
>  ifdef CONFIG_KASAN_INLINE
> @@ -27,7 +33,7 @@ else
>  	CFLAGS_KASAN := $(CFLAGS_KASAN_SHADOW) \
>  	 $(call cc-param,asan-globals=1) \
>  	 $(call cc-param,asan-instrumentation-with-call-threshold=$(call_threshold)) \
> -	 $(call cc-param,asan-stack=$(CONFIG_KASAN_STACK)) \
> +	 $(call cc-param,asan-stack=$(stack_enable)) \
>  	 $(call cc-param,asan-instrument-allocas=1)
>  endif
>  
> @@ -42,7 +48,7 @@ else
>  endif
>  
>  CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
> -		-mllvm -hwasan-instrument-stack=$(CONFIG_KASAN_STACK) \
> +		-mllvm -hwasan-instrument-stack=$(stack_enable) \
>  		-mllvm -hwasan-use-short-granules=0 \
>  		$(instrumentation_flags)
>  
> -- 
> 2.18.0
> 

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