linux-kernel - Re: [RFC PATCH v2 12/32] x86: Add early boot support when running with SEV active

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170309162942.jwtb3l33632zhbaz@pd.tnic>
Date:   Thu, 9 Mar 2017 17:29:42 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Brijesh Singh <brijesh.singh@....com>, simon.guinot@...uanux.org,
        linux-efi@...r.kernel.org, kvm@...r.kernel.org, rkrcmar@...hat.com,
        matt@...eblueprint.co.uk, linux-pci@...r.kernel.org,
        linus.walleij@...aro.org, gary.hook@....com, linux-mm@...ck.org,
        paul.gortmaker@...driver.com, hpa@...or.com, cl@...ux.com,
        dan.j.williams@...el.com, aarcange@...hat.com,
        sfr@...b.auug.org.au, andriy.shevchenko@...ux.intel.com,
        herbert@...dor.apana.org.au, bhe@...hat.com, xemul@...allels.com,
        joro@...tes.org, x86@...nel.org, peterz@...radead.org,
        piotr.luc@...el.com, mingo@...hat.com, msalter@...hat.com,
        ross.zwisler@...ux.intel.com, dyoung@...hat.com,
        thomas.lendacky@....com, jroedel@...e.de, keescook@...omium.org,
        arnd@...db.de, toshi.kani@....com, mathieu.desnoyers@...icios.com,
        luto@...nel.org, devel@...uxdriverproject.org, bhelgaas@...gle.com,
        tglx@...utronix.de, mchehab@...nel.org, iamjoonsoo.kim@....com,
        labbott@...oraproject.org, tony.luck@...el.com,
        alexandre.bounine@....com, kuleshovmail@...il.com,
        linux-kernel@...r.kernel.org, mcgrof@...nel.org, mst@...hat.com,
        linux-crypto@...r.kernel.org, tj@...nel.org,
        akpm@...ux-foundation.org, davem@...emloft.net
Subject: Re: [RFC PATCH v2 12/32] x86: Add early boot support when running
 with SEV active

On Thu, Mar 09, 2017 at 05:13:33PM +0100, Paolo Bonzini wrote:
> This is not how you check if running under a hypervisor; you should
> check the HYPERVISOR bit, i.e. bit 31 of cpuid(1).ecx.  This in turn
> tells you if leaf 0x40000000 is valid.

Ah, good point, I already do that in the microcode loader :)

        /*
         * CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
         * completely accurate as xen pv guests don't see that CPUID bit set but
         * that's good enough as they don't land on the BSP path anyway.
         */
        if (native_cpuid_ecx(1) & BIT(31))
                return *res;

> That said, the main issue with this function is that it hardcodes the
> behavior for KVM.  It is possible that another hypervisor defines its
> 0x40000001 leaf in such a way that KVM_FEATURE_SEV has a different meaning.
> 
> Instead, AMD should define a "well-known" bit in its own space (i.e.
> 0x800000xx) that is only used by hypervisors that support SEV.  This is
> similar to how Intel defined one bit in leaf 1 to say "is leaf
> 0x40000000 valid".
> 
> > +	if (eax > 0x40000000) {
> > +		eax = 0x40000001;
> > +		ecx = 0;
> > +		native_cpuid(&eax, &ebx, &ecx, &edx);
> > +		if (!(eax & BIT(KVM_FEATURE_SEV)))
> > +			goto out;
> > +
> > +		eax = 0x8000001f;
> > +		ecx = 0;
> > +		native_cpuid(&eax, &ebx, &ecx, &edx);
> > +		if (!(eax & 1))

Right, so this is testing CPUID_0x8000001f_ECX(0)[0], SME. Why not
simply set that bit for the guest too, in kvm?

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--