linux-kernel - Re: [RFC PATCH v2] x86/sev: enforce RIP-relative accesses in early SEV/SME code

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Date: Fri, 12 Jan 2024 10:29:36 -0800
From: Kevin Loughlin <kevinloughlin@...gle.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Michael Kelley <mikelley@...rosoft.com>, 
	Pankaj Gupta <pankaj.gupta@....com>, Stephen Rothwell <sfr@...b.auug.org.au>, 
	Arnd Bergmann <arnd@...db.de>, Steve Rutherford <srutherford@...gle.com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Hou Wenlong <houwenlong.hwl@...group.com>, Vegard Nossum <vegard.nossum@...cle.com>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Yuntao Wang <ytcoode@...il.com>, 
	Wang Jinchao <wangjinchao@...sion.com>, David Woodhouse <dwmw@...zon.co.uk>, 
	Brian Gerst <brgerst@...il.com>, Hugh Dickins <hughd@...gle.com>, Ard Biesheuvel <ardb@...nel.org>, 
	Joerg Roedel <jroedel@...e.de>, Randy Dunlap <rdunlap@...radead.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Dionna Glaze <dionnaglaze@...gle.com>, 
	Brijesh Singh <brijesh.singh@....com>, Michael Roth <michael.roth@....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>, Jacob Xu <jacobhxu@...gle.com>, 
	Sidharth Telang <sidtelang@...gle.com>
Subject: Re: [RFC PATCH v2] x86/sev: enforce RIP-relative accesses in early
 SEV/SME code

On Fri, Jan 12, 2024 at 4:17 AM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> Can we replace existing fixup_pointer() (and other fixup_*()) with the new
> thing? I don't think we need two confusing things for the same function.

Per my tests, yes we can; I replaced the fixup_*() functions with
GET_RIP_RELATIVE_PTR()/PTR_TO_RIP_RELATIVE_PTR(), and guests with and
without SEV, SEV-ES, and SEV-SNP all successfully booted under both
clang and gcc builds. I have a slight preference for sending that as a
separate follow-up commit, but please let me know if you feel
differently. Thanks.

> Also, is there any reason why GET_RIP_RELATIVE_PTR() and
> PTR_TO_RIP_RELATIVE_PTR() have to be macros? Inline functions would be
> cleaner.

I used macros because we need to use both the global variable itself
and the global variable's string name (obtained via #var in the macro)
in the inline assembly. As a secondary reason, the macro also avoids
the need to provide separate functions for each type of variable for
which we'd like to get RIP-relative pointers (ex: u64, unsigned int,
unsigned long, etc.).