linux-kernel - Re: [PATCH v4 01/11] x86/startup_64: Simplify global variable accesses in GDT/IDT programming

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Message-ID: <CAMj1kXG4rSGaB8Q2qFcgOH=dqS0yvR8Ofur=h5C-jq_TqiFzVg@mail.gmail.com>
Date: Tue, 13 Feb 2024 22:53:11 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, 
	Kevin Loughlin <kevinloughlin@...gle.com>, Tom Lendacky <thomas.lendacky@....com>, 
	Dionna Glaze <dionnaglaze@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH v4 01/11] x86/startup_64: Simplify global variable
 accesses in GDT/IDT programming

On Tue, 13 Feb 2024 at 21:06, Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Feb 13, 2024 at 01:41:45PM +0100, Ard Biesheuvel wrote:
> > @@ -632,5 +616,5 @@ void __head startup_64_setup_env(unsigned long physbase)
> >                    "movl %%eax, %%ss\n"
> >                    "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
> >
> > -     startup_64_load_idt(physbase);
> > +     startup_64_load_idt(&RIP_REL_REF(vc_no_ghcb));
>
> It took me a while to figure out that even if we pass in one of the two
> GHCB handler pointers, we only set it if CONFIG_AMD_MEM_ENCRYPT.
>
> I think this ontop of yours is a bit more readable as it makes it
> perfectly clear *when* the pointer is valid.
>

Looks fine to me.

> Yeah, if handler is set, we set it for the X86_TRAP_VC vector
> unconditionally but that can be changed later, if really needed.
>

We might call the parameter 'vc_handler' to make this clearer.