linux-kernel - Re: [PATCH] KVM: SVM: relax conditions for allowing MSR_IA32_SPEC

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] [day] [month] [year] [list]

Message-ID: <1d7f50a2-3c3f-dd18-a635-aa4eaa757fa3@redhat.com>
Date:   Thu, 6 Feb 2020 15:21:37 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     dgilbert@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: SVM: relax conditions for allowing
 MSR_IA32_SPEC_CTRL accesses

On 06/02/20 15:17, Vitaly Kuznetsov wrote:
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> 
> but out of pure curiosity, why do we need these checks?
> 
> At least for the 'set' case right below them we have:
> 
>         if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
>                  return 1;
> 
> so if guest will try using unsupported features it will #GP. So
> basically, these checks will only fire when reading/writing '0' and all
> features are missing, right? Do we care?

Probably not...  I just wanted the smallest possible change in semantics
for this patch, and the rest can be done equally on Intel and AMD.

Paolo