93 lines
3.4 KiB
Diff
93 lines
3.4 KiB
Diff
From adceca1789584fe567828afb7246bd35a8549e94 Mon Sep 17 00:00:00 2001
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From: Eric Northup <digitaleric@google.com>
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Date: Tue, 10 Nov 2015 13:22:52 +0100
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Subject: [PATCH 1/2] KVM: x86: work around infinite loop in microcode when #AC
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is delivered
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It was found that a guest can DoS a host by triggering an infinite
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stream of "alignment check" (#AC) exceptions. This causes the
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microcode to enter an infinite loop where the core never receives
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another interrupt. The host kernel panics pretty quickly due to the
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effects (CVE-2015-5307).
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Signed-off-by: Eric Northup <digitaleric@google.com>
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Cc: stable@vger.kernel.org
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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---
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arch/x86/include/uapi/asm/svm.h | 1 +
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arch/x86/kvm/svm.c | 8 ++++++++
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arch/x86/kvm/vmx.c | 5 ++++-
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3 files changed, 13 insertions(+), 1 deletion(-)
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diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
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index b5d7640abc5d..8a4add8e4639 100644
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--- a/arch/x86/include/uapi/asm/svm.h
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+++ b/arch/x86/include/uapi/asm/svm.h
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@@ -100,6 +100,7 @@
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{ SVM_EXIT_EXCP_BASE + UD_VECTOR, "UD excp" }, \
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{ SVM_EXIT_EXCP_BASE + PF_VECTOR, "PF excp" }, \
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{ SVM_EXIT_EXCP_BASE + NM_VECTOR, "NM excp" }, \
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+ { SVM_EXIT_EXCP_BASE + AC_VECTOR, "AC excp" }, \
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{ SVM_EXIT_EXCP_BASE + MC_VECTOR, "MC excp" }, \
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{ SVM_EXIT_INTR, "interrupt" }, \
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{ SVM_EXIT_NMI, "nmi" }, \
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diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
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index f2c8e4917688..7203b3cc71b5 100644
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--- a/arch/x86/kvm/svm.c
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+++ b/arch/x86/kvm/svm.c
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@@ -1110,6 +1110,7 @@ static void init_vmcb(struct vcpu_svm *svm)
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set_exception_intercept(svm, PF_VECTOR);
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set_exception_intercept(svm, UD_VECTOR);
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set_exception_intercept(svm, MC_VECTOR);
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+ set_exception_intercept(svm, AC_VECTOR);
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set_intercept(svm, INTERCEPT_INTR);
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set_intercept(svm, INTERCEPT_NMI);
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@@ -1798,6 +1799,12 @@ static int ud_interception(struct vcpu_svm *svm)
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return 1;
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}
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+static int ac_interception(struct vcpu_svm *svm)
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+{
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+ kvm_queue_exception_e(&svm->vcpu, AC_VECTOR, 0);
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+ return 1;
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+}
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+
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static void svm_fpu_activate(struct kvm_vcpu *vcpu)
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{
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struct vcpu_svm *svm = to_svm(vcpu);
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@@ -3362,6 +3369,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
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[SVM_EXIT_EXCP_BASE + PF_VECTOR] = pf_interception,
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[SVM_EXIT_EXCP_BASE + NM_VECTOR] = nm_interception,
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[SVM_EXIT_EXCP_BASE + MC_VECTOR] = mc_interception,
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+ [SVM_EXIT_EXCP_BASE + AC_VECTOR] = ac_interception,
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[SVM_EXIT_INTR] = intr_interception,
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[SVM_EXIT_NMI] = nmi_interception,
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[SVM_EXIT_SMI] = nop_on_interception,
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diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
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index 5eb56ed77c1f..106aa940d3c0 100644
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--- a/arch/x86/kvm/vmx.c
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+++ b/arch/x86/kvm/vmx.c
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@@ -1631,7 +1631,7 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
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u32 eb;
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eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) |
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- (1u << NM_VECTOR) | (1u << DB_VECTOR);
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+ (1u << NM_VECTOR) | (1u << DB_VECTOR) | (1u << AC_VECTOR);
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if ((vcpu->guest_debug &
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(KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) ==
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(KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP))
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@@ -5266,6 +5266,9 @@ static int handle_exception(struct kvm_vcpu *vcpu)
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return handle_rmode_exception(vcpu, ex_no, error_code);
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switch (ex_no) {
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+ case AC_VECTOR:
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+ kvm_queue_exception_e(vcpu, AC_VECTOR, error_code);
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+ return 1;
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case DB_VECTOR:
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dr6 = vmcs_readl(EXIT_QUALIFICATION);
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if (!(vcpu->guest_debug &
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--
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2.4.3
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