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

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Message-ID: <51FFD5B0.9080000@redhat.com>
Date:	Mon, 05 Aug 2013 18:41:20 +0200
From:	Laszlo Ersek <lersek@...hat.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	edk2-devel@...ts.sourceforge.net,
	David Woodhouse <dwmw2@...radead.org>,
	linux-efi@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	Gleb Natapov <gleb@...hat.com>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [edk2] Corrupted EFI region

On 08/05/13 18:12, Borislav Petkov wrote:
> On Mon, Aug 05, 2013 at 05:15:38PM +0200, Laszlo Ersek wrote:
>> The current implementation (how pointers are converted) probably doesn't
>> accommodate a second call.
>>
>> Of course you want to know why SetVirtualAddressMap() was designed like
>> that... I didn't participate in the design so I don't know :)
>>
>> But, as I said, a kernel directly executing another kernel is an
>> unexpected idea. IMHO the second kernel in question doesn't fit the UEFI
>> phases at all. The OS booted like that (ie. the OS whose kernel is the
>> 2nd (=kexec) kernel) never goes through SEC, PEI, DXE, BDS.
> 
> Yes, the thing is, imposing unnecessary restrictions is very
> counterproductive. And kexec is just an example here - if
> SetVirtualAddressMap was callable an arbitrary number of times, this
> whole work I'm doing is unnecessary. So I'm jumping through hoops just
> to accomodate a braindead design.

I doubt it was a deliberate restriction. More like, there was no
incentive (... that the designers were aware of) *not* to design
something easy (or easier) to implement. Your use case has come later.

> This is what I cannot fathom in the face of people praising UEFI as the
> solution to all problems.

I agree that such people exist. I'm not one of them.

>> BTW there's another point I'd like to ask about -- you're saying you
>> see the region corruption during the same boot, from the first (early)
>> memmap dump to the second one (when just about to enter virtual mode).
>> But, is this one boot the very first boot, or the kexec one?
> 
> No, kexec is not even involved yet. If you look at the timestamps,
> there's 0.005 seconds between the two dumps during the *same* kernel
> booting on the machine, baremetal, straight from grub.

I didn't realize the timestamps survive kexec. (As far as I remember the
kernels I played with kexec on didn't have the automatic timestamps yet
in dmesg, but I might have messed up just as well...)

Laszlo
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