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

[Kirill A. Shutemov]

On Fri, Jan 12, 2024 at 10:29:36AM -0800, Kevin Loughlin wrote:
> On Fri, Jan 12, 2024 at 4:17 AM Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> 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.

Okay good.

BTW, do we need both macros? Caller can do &var, right?

If we are okay with single macro, maybe rename it to RIP_RELATIVE_PTR().

One other thing: I see you sprinkle casts to for every use of the macros.
But why? void* can cast to any other pointer without explicit casting.

> I have a slight preference for sending that as a
> separate follow-up commit, but please let me know if you feel
> differently. Thanks.

I'm okay with a separate patch in the same patchset.

> 
> > 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.).

If we do it only on pointers, wouldn't void * -> void * be enough?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov