Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime

[H. Peter Anvin]

I think it "works" because the affected BIOSes don't put spaces between the chunks.  I have discussed this with Matt.

On September 26, 2015 10:01:14 AM PDT, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>On Fri, Sep 25, 2015 at 10:56 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>>
>> So this commit worries me.
>>
>> This bug is a good find, and the fix is obviously needed and urgent,
>but I'm not
>> sure about the implementation at all. (I've Cc:-ed a few more x86 low
>level
>> gents.)
>>
>> * Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote:
>>> +             /*
>>> +              * Starting in UEFI v2.5 the EFI_PROPERTIES_TABLE
>>> +              * config table feature requires us to map all entries
>>> +              * in the same order as they appear in the EFI memory
>>> +              * map. That is to say, entry N must have a lower
>>> +              * virtual address than entry N+1. This is because the
>>> +              * firmware toolchain leaves relative references in
>>> +              * the code/data sections, which are split and become
>>> +              * separate EFI memory regions. Mapping things
>>> +              * out-of-order leads to the firmware accessing
>>> +              * unmapped addresses.
>>> +              *
>
>I'm clearly missing something.  What is EFI doing that it doesn't care
>how big the gap between sections is but it still requires them to be
>in order?  It's not as though x86_64 has an addressing mode that
>allows only non-negative offsets.
>
>--Andy

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