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From: Liran Alon <liran.alon@oracle.com>
To: Jim Mattson <jmattson@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, kvm list <kvm@vger.kernel.org>
Subject: Re: [PATCH] kvm: nVMX: VMWRITE checks VMCS-link pointer before VMCS field
Date: Thu, 5 Dec 2019 23:54:15 +0200	[thread overview]
Message-ID: <C2F9C5D9-F106-4B89-BEFA-B3CCC0B004DE@oracle.com> (raw)
In-Reply-To: <CALMp9eTyhRwqsriLGg1xoO2sOPkgnKK1hV1U3C733xCjW7+VCA@mail.gmail.com>



> On 5 Dec 2019, at 23:30, Jim Mattson <jmattson@google.com> wrote:
> 
> On Thu, Dec 5, 2019 at 5:11 AM Jim Mattson <jmattson@google.com> wrote:
>> 
>> On Thu, Dec 5, 2019 at 3:46 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>>> 
>>> On 04/12/19 22:40, Jim Mattson wrote:
>>>> According to the SDM, a VMWRITE in VMX non-root operation with an
>>>> invalid VMCS-link pointer results in VMfailInvalid before the validity
>>>> of the VMCS field in the secondary source operand is checked.
>>>> 
>>>> Fixes: 6d894f498f5d1 ("KVM: nVMX: vmread/vmwrite: Use shadow vmcs12 if running L2")
>>>> Signed-off-by: Jim Mattson <jmattson@google.com>
>>>> Cc: Liran Alon <liran.alon@oracle.com>
>>>> ---
>>>> arch/x86/kvm/vmx/nested.c | 38 +++++++++++++++++++-------------------
>>>> 1 file changed, 19 insertions(+), 19 deletions(-)
>>> 
>>> As Vitaly pointed out, the test must be split in two, like this:
>> 
>> Right. Odd that no kvm-unit-tests noticed.
>> 
>>> ---------------- 8< -----------------------
>>> From 3b9d87060e800ffae2bd19da94ede05018066c87 Mon Sep 17 00:00:00 2001
>>> From: Paolo Bonzini <pbonzini@redhat.com>
>>> Date: Thu, 5 Dec 2019 12:39:07 +0100
>>> Subject: [PATCH] kvm: nVMX: VMWRITE checks VMCS-link pointer before VMCS field
>>> 
>>> According to the SDM, a VMWRITE in VMX non-root operation with an
>>> invalid VMCS-link pointer results in VMfailInvalid before the validity
>>> of the VMCS field in the secondary source operand is checked.
>>> 
>>> While cleaning up handle_vmwrite, make the code of handle_vmread look
>>> the same, too.
>> 
>> Okay.
>> 
>>> Fixes: 6d894f498f5d1 ("KVM: nVMX: vmread/vmwrite: Use shadow vmcs12 if running L2")
>>> Signed-off-by: Jim Mattson <jmattson@google.com>
>>> Cc: Liran Alon <liran.alon@oracle.com>
>>> 
>>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>>> index 4aea7d304beb..c080a879b95d 100644
>>> --- a/arch/x86/kvm/vmx/nested.c
>>> +++ b/arch/x86/kvm/vmx/nested.c
>>> @@ -4767,14 +4767,13 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
>>>        if (to_vmx(vcpu)->nested.current_vmptr == -1ull)
>>>                return nested_vmx_failInvalid(vcpu);
>>> 
>>> -       if (!is_guest_mode(vcpu))
>>> -               vmcs12 = get_vmcs12(vcpu);
>>> -       else {
>>> +       vmcs12 = get_vmcs12(vcpu);
>>> +       if (is_guest_mode(vcpu)) {
>>>                /*
>>>                 * When vmcs->vmcs_link_pointer is -1ull, any VMREAD
>>>                 * to shadowed-field sets the ALU flags for VMfailInvalid.
>>>                 */
>>> -               if (get_vmcs12(vcpu)->vmcs_link_pointer == -1ull)
>>> +               if (vmcs12->vmcs_link_pointer == -1ull)
>>>                        return nested_vmx_failInvalid(vcpu);
>>>                vmcs12 = get_shadow_vmcs12(vcpu);
>>>        }
>>> @@ -4878,8 +4877,19 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
>>>                }
>>>        }
>>> 
>>> +       vmcs12 = get_vmcs12(vcpu);
>>> +       if (is_guest_mode(vcpu)) {
>>> +               /*
>>> +                * When vmcs->vmcs_link_pointer is -1ull, any VMWRITE
>>> +                * to shadowed-field sets the ALU flags for VMfailInvalid.
>>> +                */
>>> +               if (vmcs12->vmcs_link_pointer == -1ull)
>>> +                       return nested_vmx_failInvalid(vcpu);
>>> +               vmcs12 = get_shadow_vmcs12(vcpu);
>>> +       }
>>> 
>>>        field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
>>> +
>>>        /*
>>>         * If the vCPU supports "VMWRITE to any supported field in the
>>>         * VMCS," then the "read-only" fields are actually read/write.
>>> @@ -4889,24 +4899,12 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
>>>                return nested_vmx_failValid(vcpu,
>>>                        VMXERR_VMWRITE_READ_ONLY_VMCS_COMPONENT);
>>> 
>>> -       if (!is_guest_mode(vcpu)) {
>>> -               vmcs12 = get_vmcs12(vcpu);
>>> -
>>> -               /*
>>> -                * Ensure vmcs12 is up-to-date before any VMWRITE that dirties
>>> -                * vmcs12, else we may crush a field or consume a stale value.
>>> -                */
>>> -               if (!is_shadow_field_rw(field))
>>> -                       copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
>>> -       } else {
>>> -               /*
>>> -                * When vmcs->vmcs_link_pointer is -1ull, any VMWRITE
>>> -                * to shadowed-field sets the ALU flags for VMfailInvalid.
>>> -                */
>>> -               if (get_vmcs12(vcpu)->vmcs_link_pointer == -1ull)
>>> -                       return nested_vmx_failInvalid(vcpu);
>>> -               vmcs12 = get_shadow_vmcs12(vcpu);
>>> -       }
>>> +       /*
>>> +        * Ensure vmcs12 is up-to-date before any VMWRITE that dirties
>>> +        * vmcs12, else we may crush a field or consume a stale value.
>>> +        */
>>> +       if (!is_guest_mode(vcpu) && !is_shadow_field_rw(field))
>>> +               copy_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
>>> 
>>>        offset = vmcs_field_to_offset(field);
>>>        if (offset < 0)
>>> 
>>> 
>>> ... and also, do you have a matching kvm-unit-tests patch?
>> 
>> I'll put one together, along with a test that shows the current
>> priority inversion between read-only and unsupported VMCS fields.
> 
> I can't figure out how to clear IA32_VMX_MISC[bit 29] in qemu, so I'm
> going to add the test to tools/testing/selftests/kvm instead.

Please don’t.

I wish that we keep clear separation between kvm-unit-tests and self-tests.
In the sense that kvm-unit-tests tests for correct CPU behaviour semantics
and self-tests tests for correctness of KVM userspace API.

In the future, I wish to change kvm-unit-tests to cpu-unit-tests. As there is no
real connection to KVM. It’s a bunch of tests that can be run on top of any CPU
Implementation (weather vCPU by some hypervisor or bare-metal CPU) and
test for it’s semantics.
I have already used this to find semantic issues on Hyper-V vCPU implementation for example.

Regarding your question on how to disable IA32_VMX_MISC in QEMU:
Paolo have recently created a patch-series for QEMU that can be used to do this.
(Aimed for QEMU nVMX Live-Migration support)
See: https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg00711.html
(You should search for final patch-series version…)

-Liran


  reply	other threads:[~2019-12-05 21:54 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-04 21:40 [PATCH] kvm: nVMX: VMWRITE checks VMCS-link pointer before VMCS field Jim Mattson
2019-12-05 11:28 ` Vitaly Kuznetsov
2019-12-05 11:45 ` Paolo Bonzini
2019-12-05 13:11   ` Jim Mattson
2019-12-05 21:30     ` Jim Mattson
2019-12-05 21:54       ` Liran Alon [this message]
2019-12-05 22:11         ` Jim Mattson
2019-12-09 15:28         ` Nadav Amit
2019-12-09 22:58           ` Liran Alon
2019-12-10 22:22             ` Nadav Amit
2019-12-09 16:12       ` Paolo Bonzini
2019-12-09 23:34         ` Jim Mattson
2019-12-10  8:39           ` Paolo Bonzini

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