[PATCH] mm/kasan: map KASAN zero page read only

[Andrey Ryabinin]

2016-01-06 18:54 GMT+03:00 Ard Biesheuvel <ard.biesheuvel at linaro.org>:
> The original x86_64-only version of KASAN mapped its zero page
> read-only, but this got lost when the code was generalised and
> ported to arm64, since, at the time, the PAGE_KERNEL_RO define
> did not exist. It has been added to arm64 in the mean time, so
> let's use it.
>

Read-only wasn't lost. Just look at the next line:
     zero_pte = pte_wrprotect(zero_pte);

PAGE_KERNEL_RO is not available on all architectures, thus it would be better
to not use it in generic code.


> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
>  mm/kasan/kasan_init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
> index 3f9a41cf0ac6..8726a92604ad 100644
> --- a/mm/kasan/kasan_init.c
> +++ b/mm/kasan/kasan_init.c
> @@ -49,7 +49,7 @@ static void __init zero_pte_populate(pmd_t *pmd, unsigned long addr,
>         pte_t *pte = pte_offset_kernel(pmd, addr);
>         pte_t zero_pte;
>
> -       zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL);
> +       zero_pte = pfn_pte(PFN_DOWN(__pa(kasan_zero_page)), PAGE_KERNEL_RO);
>         zero_pte = pte_wrprotect(zero_pte);
>
>         while (addr + PAGE_SIZE <= end) {
> --
> 2.5.0
>