Subject: Re: [PATCH v2 04/20] kasan, arm64: unpoison stack only with CONFIG_KASAN_STACK

From: Marco Elver <[email-masked]>
Date: Wed, 11 Nov 2020 17:13:13 +0100

On Tue, Nov 10, 2020 at 11:20PM +0100, Andrey Konovalov 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.
> 
> Note, that CONFIG_KASAN_STACK is an option that is currently always
> defined when CONFIG_KASAN is enabled, and therefore has to be tested
> with #if instead of #ifdef.
> 
> Signed-off-by: Andrey Konovalov <[email-masked]>
> 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(-)

Reviewed-by: Marco Elver <[email-masked]>

> 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 f22bdef82111..b9b9db335d87 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -76,8 +76,6 @@ 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);
>  
> @@ -122,8 +120,6 @@ 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) {}
>  
> @@ -175,6 +171,12 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
>  
>  #endif /* CONFIG_KASAN */
>  
> +#if defined(CONFIG_KASAN) && CONFIG_KASAN_STACK
> +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
>  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)
>  {
> -- 
> 2.29.2.222.g5d2a92d10f8-goog
> 

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