Re: [PATCH v5 2/3] mkimage: Align efi sections on 4k boundary

[Daniel Kiper]

On Fri, Jan 25, 2019 at 12:45:15PM +0100, Alexander Graf wrote:
> There is UEFI firmware popping up in the wild now that implements stricter
> permission checks using NX and write protect page table entry bits.
>
> This means that firmware now may fail to load binaries if its individual
> sections are not page aligned, as otherwise it can not ensure permission
> boundaries.
>
> So let's bump all efi section alignments up to 4k (EFI page size). That way
> we will stay compatible going forward.
>
> Unfortunately our internals can't deal very well with a mismatch of alignment
> between the virtual and file offsets, so we have to also pad our target
> binary a bit.
>
> Signed-off-by: Alexander Graf <address@hidden>
>
> ---
>
> v4 -> v5:
>
>   - Use GRUB_EFI_PAGE_SIZE
>   - Add include to have above const defined
> ---
>  include/grub/efi/pe32.h | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/include/grub/efi/pe32.h b/include/grub/efi/pe32.h
> index 7d44732d2..fe8a85ce6 100644
> --- a/include/grub/efi/pe32.h
> +++ b/include/grub/efi/pe32.h
> @@ -20,6 +20,7 @@
>  #define GRUB_EFI_PE32_HEADER 1
>
>  #include <grub/types.h>
> +#include <grub/efi/memory.h>
>
>  /* The MSDOS compatibility stub. This was copied from the output of
>     objcopy, and it is not necessary to care about what this means.  */
> @@ -50,8 +51,13 @@
>  /* According to the spec, the minimal alignment is 512 bytes...
>     But some examples (such as EFI drivers in the Intel
>     Sample Implementation) use 32 bytes (0x20) instead, and it seems
> -   to be working. For now, GRUB uses 512 bytes for safety.  */
> -#define GRUB_PE32_SECTION_ALIGNMENT  0x200
> +   to be working.
> +
> +   However, there is firmware showing up in the field now with
> +   page alignment constraints to guarantee that page protection
> +   bits take effect. Because we can not easily distinguish between
> +   in-memory and in-file layout, let's bump all alignment to 4k. */

s/4k/GRUB_EFI_PAGE_SIZE/ By chance GRUB_EFI_PAGE_SIZE is equal to 4k but
there is no requirement for that...

> +#define GRUB_PE32_SECTION_ALIGNMENT  GRUB_EFI_PAGE_SIZE

I am still missing an explanation here why GRUB_PE32_FILE_ALIGNMENT has
to be equal GRUB_PE32_SECTION_ALIGNMENT. And IIRC I have asked about
that in my earlier emails...

>  #define GRUB_PE32_FILE_ALIGNMENT     GRUB_PE32_SECTION_ALIGNMENT

Daniel