[PATCH] arm64: Honour !PTE_WRITE in set_pte_at() for kernel mappings

[Andrey Ryabinin]

2016-01-08 13:59 GMT+03:00 Ard Biesheuvel <ard.biesheuvel at linaro.org>:
>
> This works, as far as I can tell. However, I still need the patch
> below to make sure that the KAsan zero page is mapped read-only. (The
> reason is that, depending on the alignment of the regions,
> kasan_populate_zero_shadow() may never call
> zero_[pud|pmd|pte]_populate())
>
> Before this patch (and my change), the KAsan shadow regions looks like this:
>
> 0xffffff8000000000-0xffffff8200800000  8200M RW NX SHD AF     UXN MEM/NORMAL
> 0xffffff8200800000-0xffffff8200c00000     4M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffff8200c00000-0xffffff8800000000 24564M RW NX SHD AF     UXN MEM/NORMAL
> 0xffffff8800000000-0xffffff8820200000   514M RW NX SHD AF BLK UXN MEM/NORMAL
>
> and after:
>
> 0xffffff8000000000-0xffffff8200800000  8200M ro NX SHD AF     UXN MEM/NORMAL
> 0xffffff8200800000-0xffffff8200c00000     4M RW NX SHD AF BLK UXN MEM/NORMAL
> 0xffffff8200c00000-0xffffff8800000000 24564M ro NX SHD AF     UXN MEM/NORMAL
> 0xffffff8800000000-0xffffff8820200000   514M RW NX SHD AF BLK UXN MEM/NORMAL
>
>

Acked-by: Andrey Ryabinin <aryabinin at virtuozzo.com>

> ---------8<--------------
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index 72fe2978b38a..c3c14204d196 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -140,6 +140,7 @@ void __init kasan_init(void)
>  {
>         u64 kimg_shadow_start, kimg_shadow_end;
>         struct memblock_region *reg;
> +       int i;
>
>         kimg_shadow_start = round_down((u64)kasan_mem_to_shadow(_text),
>                                        SWAPPER_BLOCK_SIZE);
> @@ -185,6 +186,14 @@ void __init kasan_init(void)
>                                 pfn_to_nid(virt_to_pfn(start)));
>         }
>
> +       /*
> +        * KAsan may reuse the current contents of kasan_zero_pte
> directly, so we
> +        * should make sure that it maps the zero page read-only.
> +        */
> +       for (i = 0; i < PTRS_PER_PTE; i++)
> +               set_pte(&kasan_zero_pte[i],
> +                       pfn_pte(virt_to_pfn(kasan_zero_page), PAGE_KERNEL_RO));
> +
>         memset(kasan_zero_page, 0, PAGE_SIZE);
>         cpu_replace_ttbr1(swapper_pg_dir);