linux-kernel - Re: [PATCH v3 0/2] x86: enforce and cleanup RIP-relative accesses in early boot code

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Date: Wed, 31 Jan 2024 10:16:55 -0800
From: Jacob Xu <jacobhxu@...gle.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Kevin Loughlin <kevinloughlin@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Pankaj Gupta <pankaj.gupta@....com>, 
	Hou Wenlong <houwenlong.hwl@...group.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Dionna Glaze <dionnaglaze@...gle.com>, Brijesh Singh <brijesh.singh@....com>, 
	Michael Roth <michael.roth@....com>, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, linux-coco@...ts.linux.dev, 
	Ashish Kalra <ashish.kalra@....com>, Andi Kleen <ak@...ux.intel.com>, 
	Adam Dunlap <acdunlap@...gle.com>, Peter Gonda <pgonda@...gle.com>, 
	Sidharth Telang <sidtelang@...gle.com>
Subject: Re: [PATCH v3 0/2] x86: enforce and cleanup RIP-relative accesses in
 early boot code

On Wed, Jan 31, 2024 at 6:01 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Jan 30, 2024 at 10:08:43PM +0000, Kevin Loughlin wrote:
> > Instead, this patchset continues the approach of fixing the immediate
> > problem of SEV-SNP boots crashing when built by clang, providing a
> > backport-friendly set of changes needed to successfully boot SEV-SNP
> > hosts and guests.
>
> What use cases are those exactly? How do I reproduce them here?
>

We're interested in fixing SEV-SNP guest boots which are currently
broken when using a guest kernel compiled with clang. It seems like
every other user of SEV/SNP linux kernel code uses GCC to compile the
kernel so they've avoided this issue.

> SNP is not upstream yet and the SEV* code has been out there for a while
> now without a single such report so this must be something new happening
> due to <raisins>...?

E.g. Google COS uses clang to compile the kernel and we've made do
with an internal fix for a while. We've unfortunately just been rather
slow to report upstream.


>
> Thx.
>
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette