[RFC PATCH 2/5] kasan: allow architectures to manage the memory-to-shadow mapping

[Dmitry Vyukov]

On Fri, Feb 15, 2019 at 1:05 AM Daniel Axtens <dja at axtens.net> wrote:
>
> Currently, shadow addresses are always addr >> shift + offset.
> However, for powerpc, the virtual address space is fragmented in
> ways that make this simple scheme impractical.
>
> Allow architectures to override:
>  - kasan_shadow_to_mem
>  - kasan_mem_to_shadow
>  - addr_has_shadow
>
> Rename addr_has_shadow to kasan_addr_has_shadow as if it is
> overridden it will be available in more places, increasing the
> risk of collisions.
>
> If architectures do not #define their own versions, the generic
> code will continue to run as usual.
>
> Signed-off-by: Daniel Axtens <dja at axtens.net>

Reviewed-by: Dmitry Vyukov <dvyukov at google.com>

> ---
>  include/linux/kasan.h     | 2 ++
>  mm/kasan/generic.c        | 2 +-
>  mm/kasan/generic_report.c | 2 +-
>  mm/kasan/kasan.h          | 6 +++++-
>  mm/kasan/report.c         | 6 +++---
>  mm/kasan/tags.c           | 2 +-
>  6 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index b40ea104dd36..f6261840f94c 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -23,11 +23,13 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
>  int kasan_populate_early_shadow(const void *shadow_start,
>                                 const void *shadow_end);
>
> +#ifndef kasan_mem_to_shadow
>  static inline void *kasan_mem_to_shadow(const void *addr)
>  {
>         return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
>                 + KASAN_SHADOW_OFFSET;
>  }
> +#endif
>
>  /* Enable reporting bugs after kasan_disable_current() */
>  extern void kasan_enable_current(void);
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index ffc64a9a97a5..bafa2f986660 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -173,7 +173,7 @@ static __always_inline void check_memory_region_inline(unsigned long addr,
>         if (unlikely(size == 0))
>                 return;
>
> -       if (unlikely(!addr_has_shadow((void *)addr))) {
> +       if (unlikely(!kasan_addr_has_shadow((void *)addr))) {
>                 kasan_report(addr, size, write, ret_ip);
>                 return;
>         }
> diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c
> index 5e12035888f2..854f4de1fe10 100644
> --- a/mm/kasan/generic_report.c
> +++ b/mm/kasan/generic_report.c
> @@ -110,7 +110,7 @@ static const char *get_wild_bug_type(struct kasan_access_info *info)
>
>  const char *get_bug_type(struct kasan_access_info *info)
>  {
> -       if (addr_has_shadow(info->access_addr))
> +       if (kasan_addr_has_shadow(info->access_addr))
>                 return get_shadow_bug_type(info);
>         return get_wild_bug_type(info);
>  }
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index ea51b2d898ec..57ec24cf7bd1 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -111,16 +111,20 @@ struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
>  struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
>                                         const void *object);
>
> +#ifndef kasan_shadow_to_mem
>  static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
>  {
>         return (void *)(((unsigned long)shadow_addr - KASAN_SHADOW_OFFSET)
>                 << KASAN_SHADOW_SCALE_SHIFT);
>  }
> +#endif
>
> -static inline bool addr_has_shadow(const void *addr)
> +#ifndef kasan_addr_has_shadow
> +static inline bool kasan_addr_has_shadow(const void *addr)
>  {
>         return (addr >= kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
>  }
> +#endif
>
>  void kasan_poison_shadow(const void *address, size_t size, u8 value);
>
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index ca9418fe9232..bc3355ee2dd0 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -298,7 +298,7 @@ void kasan_report(unsigned long addr, size_t size,
>         untagged_addr = reset_tag(tagged_addr);
>
>         info.access_addr = tagged_addr;
> -       if (addr_has_shadow(untagged_addr))
> +       if (kasan_addr_has_shadow(untagged_addr))
>                 info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
>         else
>                 info.first_bad_addr = untagged_addr;
> @@ -309,11 +309,11 @@ void kasan_report(unsigned long addr, size_t size,
>         start_report(&flags);
>
>         print_error_description(&info);
> -       if (addr_has_shadow(untagged_addr))
> +       if (kasan_addr_has_shadow(untagged_addr))
>                 print_tags(get_tag(tagged_addr), info.first_bad_addr);
>         pr_err("\n");
>
> -       if (addr_has_shadow(untagged_addr)) {
> +       if (kasan_addr_has_shadow(untagged_addr)) {
>                 print_address_description(untagged_addr);
>                 pr_err("\n");
>                 print_shadow_for_address(info.first_bad_addr);
> diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> index bc759f8f1c67..cdefd0fe1f5d 100644
> --- a/mm/kasan/tags.c
> +++ b/mm/kasan/tags.c
> @@ -109,7 +109,7 @@ void check_memory_region(unsigned long addr, size_t size, bool write,
>                 return;
>
>         untagged_addr = reset_tag((const void *)addr);
> -       if (unlikely(!addr_has_shadow(untagged_addr))) {
> +       if (unlikely(!kasan_addr_has_shadow(untagged_addr))) {
>                 kasan_report(addr, size, write, ret_ip);
>                 return;
>         }
> --
> 2.19.1
>
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