linux-kernel - Re: [PATCH v12 19/46] x86/kernel: Make the .bss..decrypted section shared in RMP table

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Message-ID: <Yr8mARnQT+VZK0iy@zn.tnic>
Date:   Fri, 1 Jul 2022 18:51:13 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Michael Roth <michael.roth@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v12 19/46] x86/kernel: Make the .bss..decrypted section
 shared in RMP table

On Thu, Jun 16, 2022 at 04:41:05PM +0000, Sean Christopherson wrote:
> > I worry that another use of cc_platform_has() could creep in at some point
> > and cause the same issue. Not sure how bad it would be, performance-wise, to
> > remove the jump table optimization for arch/x86/coco/core.c.

Is there a gcc switch for that?

> One thought would be to initialize "vendor" to a bogus value, disallow calls to
> cc_set_vendor() until after the kernel as gotten to a safe point, and then WARN
> (or panic?) if cc_platform_has() is called before "vendor" is explicitly set.
> New calls can still get in, but they'll be much easier to detect and less likely
> to escape initial testing.

The invalid vendor thing makes sense but I don't think it'll help in
this case.

We set vendor in sme_enable() which comes before the

__startup_64 -> sme_postprocess_startup

path you're hitting.

We could do only the aspect of checking whether it hasn't been set yet
and warn then, in order to make the usage more robust...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette