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    SubjectRe: [PATCH RFC v2 04/21] kasan: unpoison stack only with CONFIG_KASAN_STACK
    On Thu, Oct 29, 2020 at 8:57 PM 'Andrey Konovalov' via kasan-dev
    <kasan-dev@googlegroups.com> wrote:
    >
    > On Tue, Oct 27, 2020 at 1:44 PM Dmitry Vyukov <dvyukov@google.com> wrote:
    > >
    > > 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
    >
    > CONFIG_KASAN_STACK is different from other KASAN configs. It's always
    > defined, and its value is what controls whether stack instrumentation
    > is enabled.

    Not sure why we did this instead of the following, but okay.

    config KASAN_STACK
    - int
    - default 1 if KASAN_STACK_ENABLE || CC_IS_GCC
    - default 0
    + bool
    + default y if KASAN_STACK_ENABLE || CC_IS_GCC
    + default n

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