linux-kernel - Re: [RFC PATCH] KVM: x86: Disallow KVM_SET

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: <CALMp9eR-ssCUT_6oZntZ=-5SEN7Y8q-HnraKW=WDHuAn9gYZfQ@mail.gmail.com>
Date:   Wed, 18 Dec 2019 11:38:43 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Weijiang Yang <weijiang.yang@...el.com>
Subject: Re: [RFC PATCH] KVM: x86: Disallow KVM_SET_CPUID{2} if the vCPU is in
 guest mode

On Wed, Dec 18, 2019 at 9:42 AM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Reject KVM_SET_CPUID{2} with -EBUSY if the vCPU is in guest mode (L2) to
> avoid complications and potentially undesirable KVM behavior.  Allowing
> userspace to change a guest's capabilities while L2 is active would at
> best result in unexpected behavior in the guest (L1 or L2), and at worst
> induce bad KVM behavior by breaking fundamental assumptions regarding
> transitions between L0, L1 and L2.

This seems a bit contrived. As long as we're breaking the ABI, can we
disallow changes to CPUID once the vCPU has been powered on?