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

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Date:	Sat, 26 Sep 2015 10:20:22 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>
CC:	Matt Fleming <matt@...eblueprint.co.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Matt Fleming <matt.fleming@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"Lee, Chun-Yi" <jlee@...e.com>, Borislav Petkov <bp@...e.de>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Peter Jones <pjones@...hat.com>,
	James Bottomley <JBottomley@...n.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Dave Young <dyoung@...hat.com>,
	stable <stable@...r.kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86/efi: Map EFI memmap entries in-order at runtime

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@...capital.net> wrote:
>On Fri, Sep 25, 2015 at 10:56 PM, Ingo Molnar <mingo@...nel.org> 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@...eblueprint.co.uk> 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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