linux-kernel - Re: [PATCH v3 10/10] x86, efi: EFI boot stub support

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Message-ID: <4E7B1F46.9020706@gmail.com>
Date:	Thu, 22 Sep 2011 13:43:02 +0200
From:	Maarten Lankhorst <m.b.lankhorst@...il.com>
To:	Matt Fleming <matt@...sole-pimps.org>
CC:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>,
	Matt Fleming <matt.fleming@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Mike Waychison <mikew@...gle.com>,
	Matthew Garrett <mjg@...hat.com>
Subject: Re: [PATCH v3 10/10] x86, efi: EFI boot stub support

Hey,

On 09/21/2011 02:10 PM, Matt Fleming wrote:
> From: Matt Fleming <matt.fleming@...el.com>
>
> There is currently a large divide between kernel development and the
> development of EFI boot loaders. The idea behind this patch is to give
> the kernel developers full control over the EFI boot process. As
> H. Peter Anvin put it,
>
> "The 'kernel carries its own stub' approach been very successful in
> dealing with BIOS, and would make a lot of sense to me for EFI as
> well."
>
> This patch introduces an EFI boot stub that allows an x86 bzImage to
> be loaded and executed by EFI firmware. The bzImage appears to the
> firmware as an EFI application. Luckily there are enough free bits
> within the bzImage header so that it can masquerade as an EFI
> application, thereby coercing the EFI firmware into loading it and
> jumping to its entry point. The beauty of this masquerading approach
> is that both BIOS and EFI boot loaders can still load and run the same
> bzImage, thereby allowing a single kernel image to work in any boot
> environment.
>
> The EFI boot stub supports multiple initrds, but they must exist on
> the same partition as the bzImage. Command-line arguments for the
> kernel can be appended after the bzImage name when run from the EFI
> shell, e.g.
>
> Shell> bzImage console=ttyS0 root=/dev/sdb initrd=initrd.img
>
> Cc: H. Peter Anvin <hpa@...ux.intel.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Mike Waychison <mikew@...gle.com>
> Cc: Matthew Garrett <mjg@...hat.com>
> Signed-off-by: Matt Fleming <matt.fleming@...el.com>
> ---
>
> v3:
>  - Fix following warnings when compiling CONFIG_EFI_STUB=n
>
>    arch/x86/boot/tools/build.c: In function ‘main’:
>    arch/x86/boot/tools/build.c:138:24: warning: unused variable ‘pe_header’
>    arch/x86/boot/tools/build.c:138:15: warning: unused variable ‘file_sz’
>
>  - As reported by Matthew Garrett, some Apple machines have GOPs that
>    don't have hardware attached. We need to weed these out by
>    searching for ones that handle the PCIIO protocol.
>
>  - Don't allocate memory if no initrds are on cmdline
>  - Don't trust image->load_options_size
>
>  - Maarten Lankhorst suggested:
>    - Don't strip first argument when booted from efibootmgr
>    - Don't allocate too much memory for cmdline
>    - Don't update cmdline_size, the kernel considers it read-only
>    - Don't accept '\n' for initrd names
Even if load_options_size is not always completely reliable, could you at least prevent reading more than image->load_options_size? Code below doesn't seem to do that currently..

Thanks,
Maarten
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