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

From: H. Peter Anvin
Date: Sat Sep 26 2015 - 13:22:03 EST

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
>> 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.

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