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KVM: nSVM: avoid picking up unsupported bits from L2 in int_ctl (CVE-2021-3653)

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* Invert the mask of bits that we pick from L2 in
  nested_vmcb02_prepare_control

* Invert and explicitly use VIRQ related bits bitmask in svm_clear_vintr

This fixes a security issue that allowed a malicious L1 to run L2 with
AVIC enabled, which allowed the L2 to exploit the uninitialized and enabled
AVIC to read/write the host physical memory at some offsets.

Fixes: 3d6368ef58 ("KVM: SVM: Add VMRUN handler")
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Maxim Levitsky 2021-07-15 01:56:24 +03:00 committed by Paolo Bonzini
parent 6e949ddb0a
commit 0f923e0712
3 changed files with 14 additions and 7 deletions
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2
arch/x86/include/asm/svm.h
View File

@ -184,6 +184,8 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
#define V_IGN_TPR_SHIFT 20
#define V_IGN_TPR_MASK (1 << V_IGN_TPR_SHIFT)
#define V_IRQ_INJECTION_BITS_MASK (V_IRQ_MASK | V_INTR_PRIO_MASK | V_IGN_TPR_MASK)
#define V_INTR_MASKING_SHIFT 24
#define V_INTR_MASKING_MASK (1 << V_INTR_MASKING_SHIFT)

10
arch/x86/kvm/svm/nested.c
View File

@ -503,7 +503,11 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
{
const u32 mask = V_INTR_MASKING_MASK | V_GIF_ENABLE_MASK | V_GIF_MASK;
const u32 int_ctl_vmcb01_bits =
V_INTR_MASKING_MASK | V_GIF_MASK | V_GIF_ENABLE_MASK;
const u32 int_ctl_vmcb12_bits = V_TPR_MASK | V_IRQ_INJECTION_BITS_MASK;
struct kvm_vcpu *vcpu = &svm->vcpu;
/*
@ -535,8 +539,8 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
vcpu->arch.l1_tsc_offset + svm->nested.ctl.tsc_offset;
svm->vmcb->control.int_ctl =
(svm->nested.ctl.int_ctl & ~mask) |
(svm->vmcb01.ptr->control.int_ctl & mask);
(svm->nested.ctl.int_ctl & int_ctl_vmcb12_bits) |
(svm->vmcb01.ptr->control.int_ctl & int_ctl_vmcb01_bits);
svm->vmcb->control.virt_ext = svm->nested.ctl.virt_ext;
svm->vmcb->control.int_vector = svm->nested.ctl.int_vector;

9
arch/x86/kvm/svm/svm.c
View File

@ -1589,17 +1589,18 @@ static void svm_set_vintr(struct vcpu_svm *svm)
static void svm_clear_vintr(struct vcpu_svm *svm)
{
const u32 mask = V_TPR_MASK | V_GIF_ENABLE_MASK | V_GIF_MASK | V_INTR_MASKING_MASK;
svm_clr_intercept(svm, INTERCEPT_VINTR);
/* Drop int_ctl fields related to VINTR injection. */
svm->vmcb->control.int_ctl &= mask;
svm->vmcb->control.int_ctl &= ~V_IRQ_INJECTION_BITS_MASK;
if (is_guest_mode(&svm->vcpu)) {
svm->vmcb01.ptr->control.int_ctl &= mask;
svm->vmcb01.ptr->control.int_ctl &= ~V_IRQ_INJECTION_BITS_MASK;
WARN_ON((svm->vmcb->control.int_ctl & V_TPR_MASK) !=
(svm->nested.ctl.int_ctl & V_TPR_MASK));
svm->vmcb->control.int_ctl |= svm->nested.ctl.int_ctl & ~mask;
svm->vmcb->control.int_ctl |= svm->nested.ctl.int_ctl &
V_IRQ_INJECTION_BITS_MASK;
}
vmcb_mark_dirty(svm->vmcb, VMCB_INTR);