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

From: Kevin Loughlin <kevinloughlin@google.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
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	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	 Nathan Chancellor <nathan@kernel.org>,
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	 Sidharth Telang <sidtelang@google.com>
Subject: Re: [RFC PATCH v2] x86/sev: enforce RIP-relative accesses in early SEV/SME code
Date: Fri, 12 Jan 2024 10:29:36 -0800	[thread overview]
Message-ID: <CAGdbjmLeyPhYfjVHPRa8LgNYjt9-rOPiyCodHoQOkEh9iQhjBg@mail.gmail.com> (raw)
In-Reply-To: <20240112121725.3amxlumpifhagamb@box>

On Fri, Jan 12, 2024 at 4:17 AM Kirill A. Shutemov
<kirill.shutemov@linux.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.).