linux-kernel - Re: [PATCH 3/4] KVM: nVMX: accurate emulation of MSR_IA32_CR{0,4}

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: <ebbe99dc-9725-4a34-467c-ccbbcd1c55d7@redhat.com>
Date:   Wed, 23 Nov 2016 23:11:52 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jim Mattson <jmattson@...gle.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 3/4] KVM: nVMX: accurate emulation of
 MSR_IA32_CR{0,4}_FIXED1



On 23/11/2016 23:07, David Matlack wrote:
> A downside of this scheme is we'd have to remember to update
> nested_vmx_cr4_fixed1_update() before giving VMs new CPUID bits. If we
> forget, a VM could end up with different values for CR{0,4}_FIXED0 for
> the same CPUID depending on which version of KVM you're running on.

If userspace doesn't obey KVM_GET_SUPPORTED_CPUID, all bets are off
anyway, so I don't think it's a big deal.  However, if you want to make
it generated by userspace, that would be fine as well!  That would
simply entail removing this patch, wouldn't it?

Paolo

> Hm, now I'm thinking you were right in the beginning. Userspace should
> generate CR{0,4}_FIXED1, not the kernel. And KVM should allow
> userspace to save/restore them.