Re: [PATCH RFC v2 04/21] kasan: unpoison stack only with CONFIG_KASAN_STACK

[Andrey Konovalov]

On Tue, Oct 27, 2020 at 1:44 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Thu, Oct 22, 2020 at 3:19 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> 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@xxxxxxxxxx>
> > 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

CONFIG_KASAN_STACK is different from other KASAN configs. It's always
defined, and its value is what controls whether stack instrumentation
is enabled.

>
> > +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
> >