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SubjectRe: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime
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It is still a hack unless all relative offsets are preserved.  That is actually simpler, even: no sorting necessary.

On September 26, 2015 11:15:57 AM PDT, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>On 26 September 2015 at 10:20, H. Peter Anvin <hpa@zytor.com> wrote:
>> I think it "works" because the affected BIOSes don't put spaces
>between the chunks. I have discussed this with Matt.
>>
>
>Forgive the ASCII art but perhaps an illustration might help:
>
>before the 2.5 feature, PE/COFF runtime images were remapped as
>illustrated here:
>
> PA VA
>+---------------+ +---------------+
>| | | |
>| PE/COFF .text | | EFI |
>| | | Runtime |
>+- - - - - - - -+ => | Services |----+
>| | | Code | | : :
>| PE/COFF .data | | | | : :
>| | | | | +---------------+
>+---------------+ +---------------+ | | |
>| | | | | | EFI |
>: : : : | | Runtime |
>: : : : +--->| Services |
>| | | | | Code |
>+---------------+ +---------------+ | |
>| | | | | |
>| PE/COFF .text | | EFI | +---------------+
>| | | Runtime | : gap :
>+- - - - - - - -+ => | Services |---+ +---------------+
>| | | Code | | | |
>| PE/COFF .data | | | | | EFI |
>| | | | | | Runtime |
>+---------------+ +---------------+ +---->| Services |
>| | | | | Code |
>: : : : | |
>: : : : | |
>: : : : +---------------+
>: : : : : :
>
>Since the affected symbol references only exist between PE/COFF .text
>and PE/COFF .data, there is never a problem since each is PE/COFF
>image is mapped as a single region.
>However, with the new feature enabled, this no longer holds:
> PA VA
>+---------------+ +---------------+
>| | | |
>| PE/COFF .text | | RtServices |----+
>| | | Code | |
>+- - - - - - - -+ => +---------------+ | +---------------+
>| | | RtServices | +--->| RtServices |
>| PE/COFF .data | | Data | | Code |
>| | | |----+ +---------------+
>+---------------+ +---------------+ | : gap :
>| | | | | +---------------+
>: : : : +--->| RtServices |
>: : : : | Data |
>| | | | +---------------+
>+---------------+ +---------------+ : gap :
>| | | | +---------------+
>| PE/COFF .text | | RtServices |-------->| RtServices |
>| | | Code | | Code |
>+- - - - - - - -+ => +---------------+ +---------------+
>| | | RtServices | : gap :
>| PE/COFF .data | | Data |---+ +---------------+
>| | | | | | RtServices |
>+---------------+ +---------------+ +---->| Data |
>| | | | | |
>: : : : +---------------+
>: : : : : :
>: : : : : :
>
>The illustration uses gaps, but obviously, this applies equally to
>inverting the mapping order, since the PE/COFF .text and .data
>sections will end up out of order.

--
Sent from my Android device with K-9 Mail. Please excuse my brevity.


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