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

[Alexander Graf]

On 28.01.19 13:22, Daniel Kiper wrote:
> 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...

There is, it's defined in the spec.

> 
>> +#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...

It is in the comment above exactly those 2 lines. What more do you want?


Alex