linux-kernel - Re: [PATCH v3 3/5] x86/boot/compressed/64: Check SEV encryption in 64-bit boot-path

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Date:   Wed, 28 Oct 2020 09:38:19 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Martin Radev <martin.b.radev@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/5] x86/boot/compressed/64: Check SEV encryption in
 64-bit boot-path

On Tue, Oct 27, 2020 at 12:08:12PM +0100, Borislav Petkov wrote:
> On Wed, Oct 21, 2020 at 02:39:36PM +0200, Joerg Roedel wrote:
> > diff --git a/arch/x86/kernel/sev_verify_cbit.S b/arch/x86/kernel/sev_verify_cbit.S
> > new file mode 100644
> > index 000000000000..5075458ecad0
> > --- /dev/null
> > +++ b/arch/x86/kernel/sev_verify_cbit.S
> 
> Why a separate file? You're using it just like verify_cpu.S and this is
> kinda verifying CPU so you could simply add the functionality there...

verify_cpu.S is also used on 32bit and this function is 64bit code. It
can be made working with some #ifdef'fery but I think it is cleaner to
just keep it in a separate file, also given that sev_verify_cbit() is
not needed at every place verify_cpu() is called.

> Yeah, can you please use the callee-clobbered registers in the order as
> they're used by the ABI, see arch/x86/entry/calling.h.
> 
> Because I'm looking at this and wondering are rsi, rdx and rcx somehow
> live here and you're avoiding them...

Makes sense, will update the function.

Regards,

	Joerg