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

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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: 3d6368ef58 ("KVM: SVM: Add VMRUN handler")
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Maxim Levitsky 2021-07-15 01:56:24 +03:00 committed by Greg Kroah-Hartman
parent 456fd88922
commit 7c1c96ffb6
2 changed files with 10 additions and 7 deletions
arch/x86
include/asm
svm.h
kvm
svm.c

2
arch/x86/include/asm/svm.h
View File

@ -119,6 +119,8 @@ 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)

15
arch/x86/kvm/svm.c
View File

@ -1443,12 +1443,7 @@ 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;
@ -3607,7 +3602,13 @@ 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