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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 27 Oct 2020 13:44:22 +0100
Message-ID: <CACT4Y+Zys3+VUsO6GDWQEcjCS6Wx16W_+B6aNy-fyhPcir7eeA@mail.gmail.com>
Subject: Re: [PATCH RFC v2 04/21] kasan: unpoison stack only with CONFIG_KASAN_STACK
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Kostya Serebryany <kcc@google.com>,
        Peter Collingbourne <pcc@google.com>,
        Serban Constantinescu <serbanc@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Elena Petrova <lenaptr@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Oct 22, 2020 at 3:19 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> There's a config option CONFIG_KASAN_STACK that has to be enabled for
> KASAN to use stack instrumentation and perform validity checks for
> stack variables.
>
> There's no need to unpoison stack when CONFIG_KASAN_STACK is not enabled.
> Only call kasan_unpoison_task_stack[_below]() when CONFIG_KASAN_STACK is
> enabled.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> Link: https://linux-review.googlesource.com/id/If8a891e9fe01ea543e00b576852685afec0887e3
> ---
>  arch/arm64/kernel/sleep.S        |  2 +-
>  arch/x86/kernel/acpi/wakeup_64.S |  2 +-
>  include/linux/kasan.h            | 10 ++++++----
>  mm/kasan/common.c                |  2 ++
>  4 files changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> index ba40d57757d6..bdadfa56b40e 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
>
> -#ifdef CONFIG_KASAN
> +#if defined(CONFIG_KASAN) && 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 c8daa92f38dc..5d3a0b8fd379 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
>
> -#ifdef CONFIG_KASAN
> +#if defined(CONFIG_KASAN) && 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 3f3f541e5d5f..7be9fb9146ac 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -68,8 +68,6 @@ static inline void kasan_disable_current(void) {}
>
>  void kasan_unpoison_memory(const void *address, size_t size);
>
> -void kasan_unpoison_task_stack(struct task_struct *task);
> -
>  void kasan_alloc_pages(struct page *page, unsigned int order);
>  void kasan_free_pages(struct page *page, unsigned int order);
>
> @@ -114,8 +112,6 @@ void kasan_restore_multi_shot(bool enabled);
>
>  static inline void kasan_unpoison_memory(const void *address, size_t size) {}
>
> -static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
> -
>  static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
>  static inline void kasan_free_pages(struct page *page, unsigned int order) {}
>
> @@ -167,6 +163,12 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
>
>  #endif /* CONFIG_KASAN */
>
> +#if defined(CONFIG_KASAN) && CONFIG_KASAN_STACK

&& defined(CONFIG_KASAN_STACK) for consistency

> +void kasan_unpoison_task_stack(struct task_struct *task);
> +#else
> +static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
> +#endif
> +
>  #ifdef CONFIG_KASAN_GENERIC
>
>  void kasan_cache_shrink(struct kmem_cache *cache);
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index a880e5a547ed..a3e67d49b893 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -58,6 +58,7 @@ void kasan_disable_current(void)
>  }
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>
> +#if CONFIG_KASAN_STACK

#ifdef CONFIG_ is the form used toughout the kernel code

>  static void __kasan_unpoison_stack(struct task_struct *task, const void *sp)
>  {
>         void *base = task_stack_page(task);
> @@ -84,6 +85,7 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
>
>         kasan_unpoison_memory(base, watermark - base);
>  }
> +#endif /* CONFIG_KASAN_STACK */
>
>  void kasan_alloc_pages(struct page *page, unsigned int order)
>  {
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>