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 10:01:14 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Matt Fleming <matt@...eblueprint.co.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	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

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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