Re: [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage

From: Borislav Petkov <bp@alien8.de>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
	Sergey Shatunov <me@prok.pw>,
	hpa@zytor.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	mingo@redhat.com, Thomas Gleixner <tglx@linutronix.de>,
	x86@kernel.org, linux-efi <linux-efi@vger.kernel.org>,
	initramfs@vger.kernel.org,
	Donovan Tremura <neurognostic@protonmail.ch>,
	Harald Hoyer <harald@hoyer.xyz>
Subject: Re: [PATCH 1/2] x86/boot/compressed/64: Remove .bss/.pgtable from bzImage
Date: Mon, 6 Apr 2020 13:20:42 +0200	[thread overview]
Message-ID: <20200406112042.GC2520@zn.tnic> (raw)
In-Reply-To: <CAMj1kXHAieZDvPKfjF=J+G=QVS+=XS-b4RP_=mjCEFEB_E_+Qw@mail.gmail.com>

On Mon, Apr 06, 2020 at 11:11:21AM +0200, Ard Biesheuvel wrote:
> Yes, it is in the PE/COFF specification. [0]
> 
> The whole problem is that we are conflating 'loading a PE/COFF image'
> with 'copying a PE/COFF image into memory', which are not the same
> thing. It is not just the layout issue, we are running into other
> problems with things like UEFI secure boot and TPM-based measured
> boot, where the fact that omitting the standard LoadImage() boot
> service (which takes care of these things under the hood) means that
> you now have to do your own checks and measurements. These things are
> literally all over the place at the moment, shim, GRUB, systemd-boot
> etc, with no authoritative spec that describes which component should
> be doing what.

Sounds to me like what LoadImage() does is what the authoritative spec
should be. Perhaps we should write it down as "Do what LoadImage()
does... " and then enumerate the requirements.

> Commit ec93fc371f014a6fb483e3556061ecad4b40735c has the background, but ...

Nice, I like the aspect of letting firmware do only a minimum amount of
work. :)

> ... I'll look into updating the documentation as well.

Thanks!

> Note that this stuff is hot off the press, so there may be some issues
> lurking (like this one) that we hadn't thought of yet.

Right.

> Actually, it may be sufficient to #define __efistub_global to
> __section(.data) like we already do for ARM, to ensure that these
> global flags are always initialized correctly. (I'll wait for Sergey
> to confirm that the spurious enabling of the PCI DMA protection
> resulting from this BSS issue is causing the boot regression)

Cool, but let's not jinx it. :-)

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette