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From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
	Maxim Levitsky <mlevitsk@redhat.com>
Cc: Jim Mattson <jmattson@google.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, 18 May 2021 12:59:46 +0200	[thread overview]
Message-ID: <1245ad2f-78b2-a334-e36a-524579274183@redhat.com> (raw)
In-Reply-To: <YJlluzMze2IfUM6S@google.com>

On 10/05/21 18:56, Sean Christopherson wrote:
> On Mon, May 10, 2021, Maxim Levitsky wrote:
>> On Tue, 2021-05-04 at 14:58 -0700, Jim Mattson wrote:
>>> On Tue, May 4, 2021 at 2:57 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>> On 04/05/21 23:53, Sean Christopherson wrote:
>>>>>> 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?
>>>>>
>>>>
>>>> Guest mode should mean L2.
>>>>
>>>> (I wonder if we should have a capability that says "KVM_SET_CPUID2 can
>>>> only be called prior to KVM_RUN").
>>>
>>> It would certainly make it easier to reason about potential security issues.
>>>
>> I vote too for this.
> 
> Alternatively, what about adding KVM_VCPU_RESET to let userspace explicitly
> pull RESET#, and defining that ioctl() to freeze the vCPU model?  I.e. after
> userspace resets the vCPU, KVM_SET_CPUID (and any other relevant ioctls() is
> disallowed.
> 
> Lack of proper RESET emulation is annoying, e.g. userspace has to manually stuff
> EDX after vCPU creation to get the right value at RESET.  A dedicated ioctl()
> would kill two birds with one stone, without having to add yet another "2"
> ioctl().

That has a disadvantage of opting into the more secure behavior, but we 
can do both (forbidding KVM_SET_CPUID2 after both KVM_RUN and KVM_RESET).

Paolo


  parent reply	other threads:[~2021-05-18 10:59 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
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 [this message]
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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