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Commit 42f4312c authored by Maxim Levitsky's avatar Maxim Levitsky Committed by Sasha Levin
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KVM: nSVM: avoid picking up unsupported bits from L2 in int_ctl (CVE-2021-3653) 



[ upstream commit 0f923e07124df069ba68d8bb12324398f4b6b709 ]

* 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: 3d6368ef ("KVM: SVM: Add VMRUN handler")
Signed-off-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 119d547c

arch/x86/include/asm/svm.h

+2 −0
Original line number Diff line number Diff line
@@ -118,6 +118,8 @@ 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)

arch/x86/kvm/svm.c

+8 −7
Original line number Diff line number Diff line
@@ -1444,12 +1444,7 @@ 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;
@@ -3593,7 +3588,13 @@ 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