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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Fri, 8 Jan 2021 19:56:20 +0100
Message-ID: <CAAeHK+wW3bTCvk=6v_vDQFYLC6=3kunmprXA-P=tWyXCTMZjhQ@mail.gmail.com>
Subject: Re: [PATCH v3] kasan: remove redundant config option
To:     Walter Wu <walter-zh.wu@mediatek.com>,
        Arnd Bergmann <arnd@arndb.de>
Cc:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        wsd_upstream <wsd_upstream@mediatek.com>,
        linux-mediatek@lists.infradead.org
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On Fri, Jan 8, 2021 at 5:09 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> CONFIG_KASAN_STACK and CONFIG_KASAN_STACK_ENABLE both enable KASAN stack
> instrumentation, but we should only need one config, so that we remove
> CONFIG_KASAN_STACK_ENABLE and make CONFIG_KASAN_STACK workable. see [1].
>
> When enable KASAN stack instrumentation, then 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@mediatek.com>
> Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrey Konovalov <andreyknvl@google.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Nathan Chancellor <natechancellor@gmail.com>
> ---
>
> v2: make commit log to be more readable.
> v3: remain CONFIG_KASAN_STACK_ENABLE setting
>     fix the pre-processors syntax
>
> ---
>  arch/arm64/kernel/sleep.S        |  2 +-
>  arch/x86/kernel/acpi/wakeup_64.S |  2 +-
>  include/linux/kasan.h            |  2 +-
>  lib/Kconfig.kasan                |  8 ++------
>  mm/kasan/common.c                |  2 +-
>  mm/kasan/kasan.h                 |  2 +-
>  mm/kasan/report_generic.c        |  2 +-
>  scripts/Makefile.kasan           | 10 ++++++++--
>  8 files changed, 16 insertions(+), 14 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..fde82ec85f8f 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -138,9 +138,10 @@ config KASAN_INLINE
>
>  endchoice
>
> -config KASAN_STACK_ENABLE
> +config KASAN_STACK
>         bool "Enable stack instrumentation (unsafe)" if CC_IS_CLANG && !COMPILE_TEST
>         depends on KASAN_GENERIC || KASAN_SW_TAGS
> +       default y if CC_IS_GCC
>         help
>           The LLVM stack address sanitizer has a know problem that
>           causes excessive stack usage in a lot of functions, see
> @@ -154,11 +155,6 @@ 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..bf8b073eed62 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
> +#ifdef CONFIG_KASAN_STACK
>  /* 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..4e16518d9877 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
> +#ifdef 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

AFAIR, Arnd wanted to avoid having KASAN_STACK to be enabled by
default when compiling with Clang, since Clang instrumentation leads
to very large kernel stacks, which, in turn, lead to compile-time
warnings. What I don't remember is why there are two configs.

Arnd, is that correct? What was the reason behind having two configs?