linux-kernel - Re: [PATCH v5 01/26] KVM: x86: hyper-v: Expose access to debug MSRs in the partition privilege flags

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]

Date:   Thu, 18 Aug 2022 15:14:06 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/26] KVM: x86: hyper-v: Expose access to debug MSRs
 in the partition privilege flags

On Tue, Aug 02, 2022, Vitaly Kuznetsov wrote:
> For some features, Hyper-V spec defines two separate CPUID bits: one
> listing whether the feature is supported or not and another one showing
> whether guest partition was granted access to the feature ("partition
> privilege mask"). 'Debug MSRs available' is one of such features. Add
> the missing 'access' bit.
> 
> Note: hv_check_msr_access() deliberately keeps checking
> HV_FEATURE_DEBUG_MSRS_AVAILABLE bit instead of the new HV_ACCESS_DEBUG_MSRS
> to not break existing VMMs (QEMU) which only expose one bit. Normally, VMMs
> should set either both these bits or none.

This is not the right approach long term.  If KVM absolutely cannot unconditionally
switch to checking HV_ACCESS_DEBUG_MSRS because it would break QEMU users, then we
should add a quirk, but sweeping the whole thing under the rug is wrong.