Re: [PATCHv2] arm64: Allow vmalloc regions to be set with set_memory_*

[Kees Cook]

On Tue, Jan 12, 2016 at 3:22 PM, Laura Abbott <labbott@xxxxxxxxxxxxxxxxx> wrote:
>
> The range of set_memory_* is currently restricted to the module address
> range because of difficulties in breaking down larger block sizes.
> vmalloc maps PAGE_SIZE pages so it is safe to use as well. Update the
> function ranges and add a comment explaining why the range is restricted
> the way it is.
>
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
> v2: Old version was sent out with vmalloc warnings. Sorry for the noise.
> ---
>  arch/arm64/mm/pageattr.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 3571c73..88c8e54 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -36,6 +36,26 @@ static int change_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
>         return 0;
>  }
>
> +static bool validate_addr(unsigned long start, unsigned long end)
> +{
> +       /*
> +        * This check explicitly excludes most kernel memory. Most kernel
> +        * memory is mapped with a larger page size and breaking down the
> +        * larger page size without causing TLB conflicts is very difficult.
> +        *
> +        * If you need to call set_memory_* on a range, the recommendation is
> +        * to use vmalloc since that range is mapped with pages.
> +        */
> +       if (start >= MODULES_VADDR && start < MODULES_END &&
> +           end >= MODULES_VADDR && end < MODULES_END)
> +               return true;
> +
> +       if (is_vmalloc_addr((void *)start) && is_vmalloc_addr((void *)end))
> +               return true;
> +
> +       return false;
> +}
> +
>  static int change_memory_common(unsigned long addr, int numpages,
>                                 pgprot_t set_mask, pgprot_t clear_mask)
>  {
> @@ -51,10 +71,7 @@ static int change_memory_common(unsigned long addr, int numpages,
>                 WARN_ON_ONCE(1);
>         }
>
> -       if (start < MODULES_VADDR || start >= MODULES_END)
> -               return -EINVAL;
> -
> -       if (end < MODULES_VADDR || end >= MODULES_END)
> +       if (!validate_addr(start, end))
>                 return -EINVAL;
>
>         data.set_mask = set_mask;
> --
> 2.5.0
>



-- 
Kees Cook
Chrome OS & Brillo Security