Re: [PATCH v2 2/2] kasan: Add explicit preconditions to kasan_report()

[Andrey Konovalov <andreyknvl@google.com>]

On Thu, Jan 21, 2021 at 2:20 PM Vincenzo Frascino
<vincenzo.frascino@arm.com> wrote:
>
> With the introduction of KASAN_HW_TAGS, kasan_report() dereferences
> the address passed as a parameter.
>
> Add a comment to make sure that the preconditions to the function are
> explicitly clarified.
>
> Note: An invalid address (e.g. NULL) passed to the function when,
> KASAN_HW_TAGS is enabled, leads to a kernel panic.
>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Leon Romanovsky <leonro@mellanox.com>
> Cc: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> ---
>  mm/kasan/kasan.h  | 2 +-
>  mm/kasan/report.c | 7 +++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index cc4d9e1d49b1..8c706e7652f2 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -209,7 +209,7 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
>
>  static inline bool addr_has_metadata(const void *addr)
>  {
> -       return true;
> +       return (is_vmalloc_addr(addr) || virt_addr_valid(addr));
>  }
>
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index c0fb21797550..8b690091cb37 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -403,6 +403,13 @@ static void __kasan_report(unsigned long addr, size_t size, bool is_write,
>         end_report(&flags);
>  }
>
> +/**
> + * kasan_report - report kasan fault details

print a report about a bad memory access detected by KASAN

> + * @addr: valid address of the allocation where the tag fault was detected

address of the bad access

> + * @size: size of the allocation where the tag fault was detected

size of the bad access

> + * @is_write: the instruction that caused the fault was a read or write?

whether the bad access is a write or a read

(no question mark at the end)

> + * @ip: pointer to the instruction that cause the fault

instruction pointer for the accessibility check or the bad access itself

> + */

And please move this to include/kasan/kasan.h.

>  bool kasan_report(unsigned long addr, size_t size, bool is_write,
>                         unsigned long ip)
>  {
> --
> 2.30.0
>