From 54a20552e1eae07aa240fa370a0293e006b5faed Mon Sep 17 00:00:00 2001 From: Eric Northup Date: Tue, 3 Nov 2015 18:03:53 +0100 Subject: [PATCH] KVM: x86: work around infinite loop in microcode when #AC is delivered It was found that a guest can DoS a host by triggering an infinite stream of "alignment check" (#AC) exceptions. This causes the microcode to enter an infinite loop where the core never receives another interrupt. The host kernel panics pretty quickly due to the effects (CVE-2015-5307). Signed-off-by: Eric Northup Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini --- arch/x86/include/uapi/asm/svm.h | 1 + arch/x86/kvm/svm.c | 8 ++++++++ arch/x86/kvm/vmx.c | 5 ++++- 3 files changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h index b5d7640abc5d..8a4add8e4639 100644 --- a/arch/x86/include/uapi/asm/svm.h +++ b/arch/x86/include/uapi/asm/svm.h @@ -100,6 +100,7 @@ { SVM_EXIT_EXCP_BASE + UD_VECTOR, "UD excp" }, \ { SVM_EXIT_EXCP_BASE + PF_VECTOR, "PF excp" }, \ { SVM_EXIT_EXCP_BASE + NM_VECTOR, "NM excp" }, \ + { SVM_EXIT_EXCP_BASE + AC_VECTOR, "AC excp" }, \ { SVM_EXIT_EXCP_BASE + MC_VECTOR, "MC excp" }, \ { SVM_EXIT_INTR, "interrupt" }, \ { SVM_EXIT_NMI, "nmi" }, \ diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index f2ba91990b4e..183926483c3a 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1019,6 +1019,7 @@ static void init_vmcb(struct vcpu_svm *svm) set_exception_intercept(svm, PF_VECTOR); set_exception_intercept(svm, UD_VECTOR); set_exception_intercept(svm, MC_VECTOR); + set_exception_intercept(svm, AC_VECTOR); set_intercept(svm, INTERCEPT_INTR); set_intercept(svm, INTERCEPT_NMI); @@ -1707,6 +1708,12 @@ static int ud_interception(struct vcpu_svm *svm) return 1; } +static int ac_interception(struct vcpu_svm *svm) +{ + kvm_queue_exception_e(&svm->vcpu, AC_VECTOR, 0); + return 1; +} + static void svm_fpu_activate(struct kvm_vcpu *vcpu) { struct vcpu_svm *svm = to_svm(vcpu); @@ -3270,6 +3277,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = { [SVM_EXIT_EXCP_BASE + PF_VECTOR] = pf_interception, [SVM_EXIT_EXCP_BASE + NM_VECTOR] = nm_interception, [SVM_EXIT_EXCP_BASE + MC_VECTOR] = mc_interception, + [SVM_EXIT_EXCP_BASE + AC_VECTOR] = ac_interception, [SVM_EXIT_INTR] = intr_interception, [SVM_EXIT_NMI] = nmi_interception, [SVM_EXIT_SMI] = nop_on_interception, diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index b765b036a048..89aaedd2a91d 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -1639,7 +1639,7 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu) u32 eb; eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) | - (1u << NM_VECTOR) | (1u << DB_VECTOR); + (1u << NM_VECTOR) | (1u << DB_VECTOR) | (1u << AC_VECTOR); if ((vcpu->guest_debug & (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) == (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) @@ -5261,6 +5261,9 @@ static int handle_exception(struct kvm_vcpu *vcpu) return handle_rmode_exception(vcpu, ex_no, error_code); switch (ex_no) { + case AC_VECTOR: + kvm_queue_exception_e(vcpu, AC_VECTOR, error_code); + return 1; case DB_VECTOR: dr6 = vmcs_readl(EXIT_QUALIFICATION); if (!(vcpu->guest_debug &