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From: Jim Mattson <jmattson@google.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Joerg Roedel <joro@8bytes.org>, kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Xiaoyao Li <xiaoyao.li@intel.com>,
	Reiji Watanabe <reijiw@google.com>
Subject: Re: [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be disabled in the guest
Date: Tue, 4 May 2021 15:24:04 -0700	[thread overview]
Message-ID: <CALMp9eT9HMKs_JcQHLsyc9MxFLFaAt9Ve8ev=inH-+8NeHtayw@mail.gmail.com> (raw)
In-Reply-To: <YJHGQgEE3mqUhbAc@google.com>

On Tue, May 4, 2021 at 3:10 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Tue, May 04, 2021, Jim Mattson wrote:
> > On Tue, May 4, 2021 at 2:53 PM Sean Christopherson <seanjc@google.com> wrote:
> > >
> > > On Tue, May 04, 2021, Jim Mattson wrote:
> > > > On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@google.com> wrote:
> > > > >
> > > > > Intercept RDTSCP to inject #UD if RDTSC is disabled in the guest.
> > > > >
> > > > > Note, SVM does not support intercepting RDPID.  Unlike VMX's
> > > > > ENABLE_RDTSCP control, RDTSCP interception does not apply to RDPID.  This
> > > > > is a benign virtualization hole as the host kernel (incorrectly) sets
> > > > > MSR_TSC_AUX if RDTSCP is supported, and KVM loads the guest's MSR_TSC_AUX
> > > > > into hardware if RDTSCP is supported in the host, i.e. KVM will not leak
> > > > > the host's MSR_TSC_AUX to the guest.
> > > > >
> > > > > But, when the kernel bug is fixed, KVM will start leaking the host's
> > > > > MSR_TSC_AUX if RDPID is supported in hardware, but RDTSCP isn't available
> > > > > for whatever reason.  This leak will be remedied in a future commit.
> > > > >
> > > > > Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP")
> > > > > Cc: stable@vger.kernel.org
> > > > > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > > > > ---
> > > > ...
> > > > > @@ -4007,8 +4017,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> > > > >         svm->nrips_enabled = kvm_cpu_cap_has(X86_FEATURE_NRIPS) &&
> > > > >                              guest_cpuid_has(vcpu, X86_FEATURE_NRIPS);
> > > > >
> > > > > -       /* Check again if INVPCID interception if required */
> > > > > -       svm_check_invpcid(svm);
> > > > > +       svm_recalc_instruction_intercepts(vcpu, svm);
> > > >
> > > > Does the right thing happen here if the vCPU is in guest mode when
> > > > userspace decides to toggle the CPUID.80000001H:EDX.RDTSCP bit on or
> > > > off?
> > >
> > > I hate our terminology.  By "guest mode", do you mean running the vCPU, or do
> > > you specifically mean running in L2?
> >
> > I mean is_guest_mode(vcpu) is true (i.e. running L2).
>
> No, it will not do the right thing, whatever "right thing" even means in this
> context.  That's a pre-existing issue, e.g. INVCPID handling is also wrong.
> I highly doubt VMX does, or even can, do the right thing either.
>
> I'm pretty sure I lobbied in the past to disallow KVM_SET_CPUID* if the vCPU is
> in guest mode since it's impossible to do the right thing without forcing an
> exit to L1, e.g. changing MAXPHYSADDR will allow running L2 with an illegal
> CR3, ditto for various CR4 bits.

With that caveat understood,

Reviewed-by: Jim Mattson <jmattson@google.com>

  reply	other threads:[~2021-05-04 22:24 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-04 17:17 [PATCH 00/15] KVM: x86: RDPID/RDTSCP fixes and uret MSR cleanups Sean Christopherson
2021-05-04 17:17 ` [PATCH 01/15] KVM: VMX: Do not adverise RDPID if ENABLE_RDTSCP control is unsupported Sean Christopherson
2021-05-04 17:37   ` Jim Mattson
2021-05-04 17:53     ` Jim Mattson
2021-05-04 18:14       ` Sean Christopherson
2021-05-05  3:04   ` Reiji Watanabe
2021-05-10  8:03   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 02/15] KVM: x86: Emulate RDPID only if RDTSCP is supported Sean Christopherson
2021-05-04 17:50   ` Jim Mattson
2021-05-05  3:51   ` Reiji Watanabe
2021-05-05  8:01     ` Paolo Bonzini
2021-05-10  8:08   ` Maxim Levitsky
2021-05-10 17:20     ` Sean Christopherson
2021-05-11 12:32       ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be disabled in the guest Sean Christopherson
2021-05-04 21:45   ` Jim Mattson
2021-05-04 21:53     ` Sean Christopherson
2021-05-04 21:56       ` Jim Mattson
2021-05-04 22:10         ` Sean Christopherson
2021-05-04 22:24           ` Jim Mattson [this message]
2021-05-04 21:57       ` Paolo Bonzini
2021-05-04 21:58         ` Jim Mattson
2021-05-10  8:08           ` Maxim Levitsky
2021-05-10 16:56             ` Sean Christopherson
2021-05-11 12:34               ` Maxim Levitsky
2021-05-18 10:59               ` Paolo Bonzini
2021-05-18 19:24                 ` Sean Christopherson
2021-05-05  4:26   ` Reiji Watanabe
2021-05-10  8:08   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 04/15] KVM: x86: Move RDPID emulation intercept to its own enum Sean Christopherson
2021-05-04 23:24   ` Jim Mattson
2021-05-10  8:14   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 05/15] KVM: VMX: Disable preemption when probing user return MSRs Sean Christopherson
2021-05-04 23:36   ` Jim Mattson
2021-05-10  8:18   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 06/15] KVM: SVM: Probe and load MSR_TSC_AUX regardless of RDTSCP support in host Sean Christopherson
2021-05-10  8:20   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 07/15] KVM: x86: Add support for RDPID without RDTSCP Sean Christopherson
2021-05-10  8:20   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 08/15] KVM: VMX: Configure list of user return MSRs at module init Sean Christopherson
2021-05-10  8:23   ` Maxim Levitsky
2021-05-10 15:13     ` Sean Christopherson
2021-05-11 12:34       ` Maxim Levitsky
2021-05-11 20:10         ` Sean Christopherson
2021-05-04 17:17 ` [PATCH 09/15] KVM: VMX: Use flag to indicate "active" uret MSRs instead of sorting list Sean Christopherson
2021-05-08  3:31   ` Reiji Watanabe
2021-05-10 16:43     ` Sean Christopherson
2021-05-10 17:55       ` Reiji Watanabe
2021-05-10  8:25   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 10/15] KVM: VMX: Use common x86's uret MSR list as the one true list Sean Christopherson
2021-05-10  8:25   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 11/15] KVM: VMX: Disable loading of TSX_CTRL MSR the more conventional way Sean Christopherson
2021-05-05  8:49   ` Paolo Bonzini
2021-05-05 15:36     ` Sean Christopherson
2021-05-05 15:50       ` Paolo Bonzini
2021-05-10  8:26   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 12/15] KVM: x86: Export the number of uret MSRs to vendor modules Sean Christopherson
2021-05-10  8:27   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 13/15] KVM: x86: Move uret MSR slot management to common x86 Sean Christopherson
2021-05-10  8:28   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 14/15] KVM: x86: Tie Intel and AMD behavior for MSR_TSC_AUX to guest CPU model Sean Christopherson
2021-05-10  8:29   ` Maxim Levitsky
2021-05-10 16:50     ` Sean Christopherson
2021-05-10 17:11       ` Jim Mattson
2021-05-11 12:34         ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 15/15] KVM: x86: Hide RDTSCP and RDPID if MSR_TSC_AUX probing failed Sean Christopherson
2021-05-10  8:29   ` Maxim Levitsky
2021-05-05  8:51 ` [PATCH 00/15] KVM: x86: RDPID/RDTSCP fixes and uret MSR cleanups Paolo Bonzini

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