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KVM: x86: nSVM: Cache and validate vmcb12 g_pat

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When KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT is disabled and nested paging is
enabled in vmcb12, validate g_pat at emulated VMRUN and cause an immediate
VMEXIT with exit code VMEXIT_INVALID if it is invalid, as specified in the
APM, volume 2: "Nested Paging and VMRUN/VMEXIT."

Fixes: 3d6368ef58 ("KVM: SVM: Add VMRUN handler")
Signed-off-by: Jim Mattson <jmattson@google.com>
Link: https://patch.msgid.link/20260407190343.325299-4-jmattson@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Jim Mattson 2026-04-07 12:03:26 -07:00 committed by Sean Christopherson
parent 0a8aeb1584
commit 4b83e4ba83
2 changed files with 20 additions and 4 deletions
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23
arch/x86/kvm/svm/nested.c
View File

@ -411,7 +411,8 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
/* Common checks that apply to both L1 and L2 state. */
static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu,
struct vmcb_save_area_cached *save)
struct vmcb_save_area_cached *save,
bool check_gpat)
{
if (CC(!(save->efer & EFER_SVME)))
return false;
@ -446,6 +447,15 @@ static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu,
if (CC(!kvm_valid_efer(vcpu, save->efer)))
return false;
/*
* If userspace contrives to get an invalid g_pat into vmcb02 by
* disabling KVM_X86_QUIRK_NESTED_SVM_SHARED_PAT in a race with
* this check, it should be prepared for the KVM_EXIT_FAIL_ENTRY
* that will follow.
*/
if (check_gpat && CC(!kvm_pat_valid(save->g_pat)))
return false;
return true;
}
@ -453,7 +463,8 @@ int nested_svm_check_cached_vmcb12(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
if (!nested_vmcb_check_save(vcpu, &svm->nested.save) ||
if (!nested_vmcb_check_save(vcpu, &svm->nested.save,
l2_has_separate_pat(vcpu)) ||
!nested_vmcb_check_controls(vcpu, &svm->nested.ctl))
return -EINVAL;
@ -566,6 +577,7 @@ static void __nested_copy_vmcb_save_to_cache(struct vmcb_save_area_cached *to,
to->rax = from->rax;
to->cr2 = from->cr2;
to->g_pat = from->g_pat;
svm_copy_lbrs(to, from);
}
@ -1982,13 +1994,16 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
/*
* Validate host state saved from before VMRUN (see
* nested_svm_check_permissions).
* nested_svm_check_permissions). Note that the g_pat field is not
* validated, because (a) it may have been clobbered by SMM before
* KVM_GET_NESTED_STATE, and (b) it is not loaded at emulated
* #VMEXIT.
*/
__nested_copy_vmcb_save_to_cache(&save_cached, save);
if (!(save->cr0 & X86_CR0_PG) ||
!(save->cr0 & X86_CR0_PE) ||
(save->rflags & X86_EFLAGS_VM) ||
!nested_vmcb_check_save(vcpu, &save_cached))
!nested_vmcb_check_save(vcpu, &save_cached, false))
goto out_free;

1
arch/x86/kvm/svm/svm.h
View File

@ -167,6 +167,7 @@ struct vmcb_save_area_cached {
u64 isst_addr;
u64 rax;
u64 cr2;
u64 g_pat;
u64 dbgctl;
u64 br_from;
u64 br_to;