Re: [PATCH 2/5 v4] KVM: nSVM: Check addresses of MSR and IO permission maps

Krish Sadhukhan
2021-03-25T01:18:15Z

On 3/24/21 12:15 PM, Sean Christopherson wrote:
> On Wed, Mar 24, 2021, Krish Sadhukhan wrote:
>> According to section "Canonicalization and Consistency Checks" in APM vol 2,
>> the following guest state is illegal:
>>
>> "The MSR or IOIO intercept tables extend to a physical address that
>> is greater than or equal to the maximum supported physical address."
>>
>> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
>> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
>> ---
>> arch/x86/kvm/svm/nested.c | 28 +++++++++++++++++++++-------
>> 1 file changed, 21 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
>> index 35891d9a1099..b08d1c595736 100644
>> --- a/arch/x86/kvm/svm/nested.c
>> +++ b/arch/x86/kvm/svm/nested.c
>> @@ -231,7 +231,15 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
>> return true;
>> }
>>
>> -static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
>> +static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa,
>> + u8 order)
>> +{
>> + u64 last_pa = PAGE_ALIGN(pa) + (PAGE_SIZE << order) - 1;
> Ugh, I really wish things that "must" happen were actually enforced by hardware.
>
> The MSRPM must be aligned on a 4KB boundary... The VMRUN instruction ignores
> the lower 12 bits of the address specified in the VMCB.
>
> So, ignoring an unaligned @pa is correct, but that means
> nested_svm_exit_handled_msr() and nested_svm_intercept_ioio() are busted.

How about we call PAGE_ALIGN() on the addresses where they are allocated
i.e., in svm_vcpu_alloc_msrpm() and in svm_hardware_setup() ? That way
even if we are not checking for alignment here, we are still good.

>
>> + return last_pa > pa && !(last_pa >> cpuid_maxphyaddr(vcpu));
> Please use kvm_vcpu_is_legal_gpa().
>
>> +}
>> +
>> +static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
>> + struct vmcb_control_area *control)
>> {
>> if ((vmcb_is_intercept(control, INTERCEPT_VMRUN)) == 0)
>> return false;
>> @@ -243,12 +251,18 @@ static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
>> !npt_enabled)
>> return false;
>>
>> + if (!nested_svm_check_bitmap_pa(vcpu, control->msrpm_base_pa,
>> + MSRPM_ALLOC_ORDER))
>> + return false;
>> + if (!nested_svm_check_bitmap_pa(vcpu, control->iopm_base_pa,
>> + IOPM_ALLOC_ORDER))
> I strongly dislike using the alloc orders, relying on kernel behavior to
> represent architectural values it sketchy. Case in point, IOPM_ALLOC_ORDER is a
> 16kb size, whereas the actual size of the IOPM is 12kb.

You're right, the IOPM check is wrong.

> I also called this out
> in v1...
>
> https://urldefense.com/v3/__https://lkml.kernel.org/r/YAd9MBkpDjC1MY6E@google.com__;!!GqivPVa7Brio!PkV46MQtWW8toodVKSwtWy_wKBPlsT8ME0Y_NND8Xs05NJir6WSNS4ndmhVuqW9N3Jef$

OK, I will define the actual size.

BTW, can we can switch to alloc_pages_exact() instead of alloc_pages()
for allocating the IOPM bitmap ? The IOPM stays allocated throughout the
lifetime of the guest and hence it won't impact performance much.

>> + return false;
>> +
>> return true;
>> }
>>
>> -static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12)
>> +static bool nested_vmcb_checks(struct kvm_vcpu *vcpu, struct vmcb *vmcb12)
>> {
>> - struct kvm_vcpu *vcpu = &svm->vcpu;
>> bool vmcb12_lma;
>>
>> if ((vmcb12->save.efer & EFER_SVME) == 0)
>> @@ -268,10 +282,10 @@ static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12)
>> kvm_vcpu_is_illegal_gpa(vcpu, vmcb12->save.cr3))
>> return false;
>> }
>> - if (!kvm_is_valid_cr4(&svm->vcpu, vmcb12->save.cr4))
>> + if (!kvm_is_valid_cr4(vcpu, vmcb12->save.cr4))
>> return false;
>>
>> - return nested_vmcb_check_controls(&vmcb12->control);
>> + return nested_vmcb_check_controls(vcpu, &vmcb12->control);
>> }
>>
>> static void load_nested_vmcb_control(struct vcpu_svm *svm,
>> @@ -515,7 +529,7 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
>> if (WARN_ON_ONCE(!svm->nested.initialized))
>> return -EINVAL;
>>
>> - if (!nested_vmcb_checks(svm, vmcb12)) {
>> + if (!nested_vmcb_checks(&svm->vcpu, vmcb12)) {
> Please use @vcpu directly.

It's all cleaned up in patch# 3.

> Looks like this needs a rebase, as the prototype for
> nested_svm_vmrun() is wrong relative to kvm/queue.
>
>> vmcb12->control.exit_code = SVM_EXIT_ERR;
>> vmcb12->control.exit_code_hi = 0;
>> vmcb12->control.exit_info_1 = 0;
>> @@ -1191,7 +1205,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>> goto out_free;
>>
>> ret = -EINVAL;
>> - if (!nested_vmcb_check_controls(ctl))
>> + if (!nested_vmcb_check_controls(vcpu, ctl))
>> goto out_free;
>>
>> /*
>> --
>> 2.27.0
>>