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

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Message-ID: <CAMj1kXGh9pw0U=+-Pg8Uh4xzNhyDZBDvGC7jcnCYvmTQxaUZTQ@mail.gmail.com>
Date: Sat, 3 Feb 2024 11:27:19 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Kevin Loughlin <kevinloughlin@...gle.com>, Jacob Xu <jacobhxu@...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>, 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 Sat, 3 Feb 2024 at 11:20, Borislav Petkov <bp@...en8.de> wrote:
>
> On Fri, Feb 02, 2024 at 04:22:02PM -0800, Kevin Loughlin wrote:
> > True. I just think it would be better to have an upstream fix for
> > clang builds of SEV-SNP guests; I believe the first such SEV-SNP code
> > was merged in 5.19 if I'm not mistaken.
>
> SNP host support is not upstream yet. So we'd be supporting something
> which is out-of-tree. Lemme see how ugly it'll get...
>

The minimal fix doesn't look that bad IMHO. Note that this version is
based on your patch that removes
CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT, and we'd need to see whether
or not to backport that as well.

 arch/x86/include/asm/asm.h         | 13 +++++++++++++
 arch/x86/include/asm/mem_encrypt.h | 13 ++++++++-----
 arch/x86/kernel/sev-shared.c       | 12 ++++++------
 arch/x86/kernel/sev.c              |  9 +++++++--
 arch/x86/mm/mem_encrypt_identity.c | 27 ++++++++++++---------------
 5 files changed, 46 insertions(+), 28 deletions(-)

https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?h=x86-pie-for-sev-v4a&id=65d0e5f4ed6ca807cdf28a1c5c0389af2c9f9bda