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Date:   Fri, 8 Jan 2021 09:38:30 +0800
From:   Walter Wu <walter-zh.wu@...iatek.com>
To:     Nathan Chancellor <natechancellor@...il.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, 2021-01-07 at 14:00 -0700, Nathan Chancellor wrote:
> 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.
> 

Ok, I will remain this.

> > +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?
> 

Yes, I will fix in the next version. Thanks for your review.

> >  /* 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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