linux-kernel - Re: [PATCH 2/2] KVM: VMX: Add knob to allow rejecting kvm

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: <Yo7Np1N1TVD4drxc@google.com>
Date:   Thu, 26 May 2022 00:45:27 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chenyi Qiang <chenyi.qiang@...el.com>,
        Lei Wang <lei4.wang@...el.com>
Subject: Re: [PATCH 2/2] KVM: VMX: Add knob to allow rejecting kvm_intel on
 inconsistent VMCS config

On Wed, May 25, 2022, Jim Mattson wrote:
> On Wed, May 25, 2022 at 2:04 PM Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > Add an off-by-default module param, reject_inconsistent_vmcs_config, to
> > allow rejecting the load of kvm_intel if an inconsistent VMCS config is
> > detected.  Continuing on with an inconsistent, degraded config is
> > undesirable when the CPU is expected to support a given set of features,
> > e.g. can result in a misconfigured VM if userspace doesn't cross-check
> > KVM_GET_SUPPORTED_CPUID, and/or can result in poor performance due to
> > lack of fast MSR switching.
> >
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> There are several inconsistent VMCS configs that are not rejected here
> (e.g. "enable XSAVES/XRSTORS" on a CPU that doesn't support XSAVES).
> Do you plan to include more checks in the future, or should this be,
> "reject_some_inconsistent_vmcs_configs"? :-)

I have no plan, it was purely a reaction to continuing on with a known bad entry/exit
pair handling being awful.  I hesitated to even apply it to the EPT/VPID stuff, but
again it seemed silly to detect an inconsistency and do nothing about it.

I'm not opposed to adding more checks, though there is definitely a point of
diminishing returns.  I'm just picking the really low hanging fruit :-)