[PATCH 2/2] arm64: fixmap: check idx is definitely valid

[Ard Biesheuvel]

On 4 March 2015 at 14:27, Mark Rutland <mark.rutland at arm.com> wrote:
> Fixmap indices are in the interval (FIX_HOLE, __end_of_fixed_addresses),
> but in __set_fixmap we only check idx <= __end_of_fixed_addresses, and
> therefore indices <= FIX_HOLE are erroneously accepted. If called with
> such an idx, __set_fixmap may corrupt page tables outside of the fixmap
> region.
>
> This patch ensures that we validate the idx against both endpoints of
> the interval.
>
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Kees Cook <keescook at chromium.org>
> Cc: Laura Abbott <lauraa at codeaurora.org>
> Cc: Will Deacon <will.deacon at arm.com>

Acked-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

> ---
>  arch/arm64/mm/mmu.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index c6daaf6..c9267ac 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -627,10 +627,7 @@ void __set_fixmap(enum fixed_addresses idx,
>         unsigned long addr = __fix_to_virt(idx);
>         pte_t *pte;
>
> -       if (idx >= __end_of_fixed_addresses) {
> -               BUG();
> -               return;
> -       }
> +       BUG_ON(idx <= FIX_HOLE || idx >= __end_of_fixed_addresses);
>
>         pte = fixmap_pte(addr);
>
> --
> 1.9.1
>