Re: [PATCH v9 16/44] kasan, arm64: only use kasan_depth for software modes

[Alexander Potapenko <glider@google.com>]

On Tue, Nov 10, 2020 at 11:11 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> This is a preparatory commit for the upcoming addition of a new hardware
> tag-based (MTE-based) KASAN mode.
>
> Hardware tag-based KASAN won't use kasan_depth. Only define and use it
> when one of the software KASAN modes are enabled.
>
> No functional changes for software modes.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

> ---
> Change-Id: I6109ea96c8df41ef6d75ad71bf22c1c8fa234a9a
> ---
>  arch/arm64/mm/kasan_init.c | 11 ++++++++---
>  include/linux/kasan.h      | 18 +++++++++---------
>  include/linux/sched.h      |  2 +-
>  init/init_task.c           |  2 +-
>  mm/kasan/common.c          |  2 ++
>  mm/kasan/report.c          |  2 ++
>  6 files changed, 23 insertions(+), 14 deletions(-)
>
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index ffeb80d5aa8d..5172799f831f 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -273,17 +273,22 @@ static void __init kasan_init_shadow(void)
>         cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
>  }
>
> +static void __init kasan_init_depth(void)
> +{
> +       init_task.kasan_depth = 0;
> +}
> +
>  #else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS) */
>
>  static inline void __init kasan_init_shadow(void) { }
>
> +static inline void __init kasan_init_depth(void) { }
> +
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>
>  void __init kasan_init(void)
>  {
>         kasan_init_shadow();
> -
> -       /* At this point kasan is fully initialized. Enable error messages */
> -       init_task.kasan_depth = 0;
> +       kasan_init_depth();
>         pr_info("KernelAddressSanitizer initialized\n");
>  }
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index f6435b9f889c..979d598e1c30 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -51,6 +51,12 @@ static inline void *kasan_mem_to_shadow(const void *addr)
>  int kasan_add_zero_shadow(void *start, unsigned long size);
>  void kasan_remove_zero_shadow(void *start, unsigned long size);
>
> +/* Enable reporting bugs after kasan_disable_current() */
> +extern void kasan_enable_current(void);
> +
> +/* Disable reporting bugs for current task */
> +extern void kasan_disable_current(void);
> +
>  #else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>
>  static inline int kasan_add_zero_shadow(void *start, unsigned long size)
> @@ -61,16 +67,13 @@ static inline void kasan_remove_zero_shadow(void *start,
>                                         unsigned long size)
>  {}
>
> +static inline void kasan_enable_current(void) {}
> +static inline void kasan_disable_current(void) {}
> +
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>
>  #ifdef CONFIG_KASAN
>
> -/* Enable reporting bugs after kasan_disable_current() */
> -extern void kasan_enable_current(void);
> -
> -/* Disable reporting bugs for current task */
> -extern void kasan_disable_current(void);
> -
>  void kasan_unpoison_memory(const void *address, size_t size);
>
>  void kasan_unpoison_task_stack(struct task_struct *task);
> @@ -121,9 +124,6 @@ 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_enable_current(void) {}
> -static inline void kasan_disable_current(void) {}
> -
>  static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
>  static inline void kasan_free_pages(struct page *page, unsigned int order) {}
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 063cd120b459..81b09bd31186 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1197,7 +1197,7 @@ struct task_struct {
>         u64                             timer_slack_ns;
>         u64                             default_timer_slack_ns;
>
> -#ifdef CONFIG_KASAN
> +#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
>         unsigned int                    kasan_depth;
>  #endif
>
> diff --git a/init/init_task.c b/init/init_task.c
> index a56f0abb63e9..39703b4ef1f1 100644
> --- a/init/init_task.c
> +++ b/init/init_task.c
> @@ -176,7 +176,7 @@ struct task_struct init_task
>         .numa_group     = NULL,
>         .numa_faults    = NULL,
>  #endif
> -#ifdef CONFIG_KASAN
> +#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
>         .kasan_depth    = 1,
>  #endif
>  #ifdef CONFIG_KCSAN
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 543e6bf2168f..d0b3ff410b0c 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -46,6 +46,7 @@ void kasan_set_track(struct kasan_track *track, gfp_t flags)
>         track->stack = kasan_save_stack(flags);
>  }
>
> +#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
>  void kasan_enable_current(void)
>  {
>         current->kasan_depth++;
> @@ -55,6 +56,7 @@ void kasan_disable_current(void)
>  {
>         current->kasan_depth--;
>  }
> +#endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>
>  static void __kasan_unpoison_stack(struct task_struct *task, const void *sp)
>  {
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index b18d193f7f58..af9138ea54ad 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -292,8 +292,10 @@ static void print_shadow_for_address(const void *addr)
>
>  static bool report_enabled(void)
>  {
> +#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
>         if (current->kasan_depth)
>                 return false;
> +#endif
>         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
>                 return true;
>         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
> --
> 2.29.2.222.g5d2a92d10f8-goog
>


-- 
Alexander Potapenko
Software Engineer

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