[SRU Bionic 2/2] KVM: nSVM: avoid picking up unsupported bits from L2 in int_ctl (CVE-2021-3653)

[Thadeu Lima de Souza Cascardo]

From: Maxim Levitsky <mlevitsk at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1940134

commit 0f923e07124df069ba68d8bb12324398f4b6b709 upstream.

* 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: 3d6368ef580a ("KVM: SVM: Add VMRUN handler")
Signed-off-by: Maxim Levitsky <mlevitsk at redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 4d9059df57cb3b8ff07cea55ba439fa3c846ef80 linux-5.4.y)
CVE-2021-3653
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 arch/x86/include/asm/svm.h |  2 ++
 arch/x86/kvm/svm.c         | 15 ++++++++-------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 78dd9df88157..2a9e81e93aac 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -117,6 +117,8 @@ 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)
 
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index db07c4131318..369cd5e2a573 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1215,12 +1215,7 @@ static __init int svm_hardware_setup(void)
 		}
 	}
 
-	if (vgif) {
-		if (!boot_cpu_has(X86_FEATURE_VGIF))
-			vgif = false;
-		else
-			pr_info("Virtual GIF supported\n");
-	}
+	vgif = false; /* Disabled for CVE-2021-3653 */
 
 	return 0;
 
@@ -3134,7 +3129,13 @@ static void enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
 	svm->nested.intercept            = nested_vmcb->control.intercept;
 
 	svm_flush_tlb(&svm->vcpu, true);
-	svm->vmcb->control.int_ctl = nested_vmcb->control.int_ctl | V_INTR_MASKING_MASK;
+
+	svm->vmcb->control.int_ctl &=
+			V_INTR_MASKING_MASK | V_GIF_ENABLE_MASK | V_GIF_MASK;
+
+	svm->vmcb->control.int_ctl |= nested_vmcb->control.int_ctl &
+			(V_TPR_MASK | V_IRQ_INJECTION_BITS_MASK);
+
 	if (nested_vmcb->control.int_ctl & V_INTR_MASKING_MASK)
 		svm->vcpu.arch.hflags |= HF_VINTR_MASK;
 	else
-- 
2.30.2