> On 5 Dec 2019, at 23:30, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>
> On Thu, Dec 5, 2019 at 5:11 AM Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>>
>> On Thu, Dec 5, 2019 at 3:46 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>> Cc: Liran Alon <liran.alon@xxxxxxxxxx>
>>>> ---
>>>> 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@xxxxxxxxxx>
>>> 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@xxxxxxxxxx>
>>> Cc: Liran Alon <liran.alon@xxxxxxxxxx>
>>>
>>> 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
