[PATCH] arm64: efi: ignore EFI_MEMORY_XP attribute if RP and/or WP are set

[Ard Biesheuvel]

On 14 September 2017 at 12:31, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> The UEFI memory map

*spec*

> is a bit vague about how to interpret the
> EFI_MEMORY_XP attribute when it is combined with EFI_MEMORY_RP and/or
> EFI_MEMORY_WP, which have retroactively been redefined as cacheability
> attributes rather than permission attributes.
>
> So let's ignore EFI_MEMORY_XP if _RP and/or _WP are also set. In this
> case, it is likely that they are being used to describe the capability
> of the region (i.e., whether it has the controls to reconfigure it as
> non-executable) rather than the nature of the contents of the region
> (i.e., whether it contains data that we will never attempt to execute)
>
> Cc: Stephen Boyd <sboyd at codeaurora.org>
> Cc: Matt Fleming <matt at codeblueprint.co.uk>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
>  arch/arm64/kernel/efi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> index 82cd07592519..f85ac58d08a3 100644
> --- a/arch/arm64/kernel/efi.c
> +++ b/arch/arm64/kernel/efi.c
> @@ -48,7 +48,9 @@ static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)
>                 return pgprot_val(PAGE_KERNEL_ROX);
>
>         /* RW- */
> -       if (attr & EFI_MEMORY_XP || type != EFI_RUNTIME_SERVICES_CODE)
> +       if (((attr & (EFI_MEMORY_RP | EFI_MEMORY_WP | EFI_MEMORY_XP)) ==
> +            EFI_MEMORY_XP) ||
> +           type != EFI_RUNTIME_SERVICES_CODE)
>                 return pgprot_val(PAGE_KERNEL);
>
>         /* RWX */
> --
> 2.11.0
>