linux-kernel - Re: [edk2] Corrupted EFI region

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Message-ID: <1375743157.18481.14.camel@dabdike.int.hansenpartnership.com>
Date:	Mon, 05 Aug 2013 15:52:37 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Laszlo Ersek <lersek@...hat.com>
Cc:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Fish <afish@...le.com>,
	edk2-devel@...ts.sourceforge.net, linux-efi@...r.kernel.org,
	Gleb Natapov <gleb@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [edk2] Corrupted EFI region

On Mon, 2013-08-05 at 23:55 +0200, Laszlo Ersek wrote:
> On 08/05/13 23:41, Borislav Petkov wrote:
> > On Mon, Aug 05, 2013 at 02:37:08PM -0700, H. Peter Anvin wrote:
> >> All of this would be a non-problem if there weren't buggy
> >> implementations which can't run *without* SetVirtualAddressMap().
> > 
> > Oh, you mean, if we were to call the runtime services through their
> > physical addresses?
> 
> I heard that there was a (U)EFI firmware implementation that didn't even
> implement SetVirtualAddressMap(). It was okay because the main OS for
> that platform didn't want to call it, it thunked to physical mode for
> each runtime service call.
> 
> (This is not hearsay; I'm omitting the specifics because I'm not sure if
> I'm allowed to give any. I've heard about this stuff from a direct
> colleague who used to work on these systems.)

That's actually the way all non-x86 unix systems operate.  If you look
in the firmware mechanisms for almost every non-x86 system in the Linux
kernel architecture directories they do this if they have to access
firmware from Linux (we do it a lot on parisc to get the IODC to give us
the device inventory for instance).

I strongly suspect the origin of this weirdness is that once upon a time
windows didn't run with a separated address space and so needed a way of
accessing firmware in the same address space, hence the pointer
relocation trick, but even windows hasn't needed this for a while.

James


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