From add5ff7a216ee545a214013f26d1ef2f44a9c9f8 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 23 Mar 2018 09:34:00 -0700 Subject: KVM: VMX: raise internal error for exception during invalid protected mode state MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Exit to userspace with KVM_INTERNAL_ERROR_EMULATION if we encounter an exception in Protected Mode while emulating guest due to invalid guest state. Unlike Big RM, KVM doesn't support emulating exceptions in PM, i.e. PM exceptions are always injected via the VMCS. Because we will never do VMRESUME due to emulation_required, the exception is never realized and we'll keep emulating the faulting instruction over and over until we receive a signal. Exit to userspace iff there is a pending exception, i.e. don't exit simply on a requested event. The purpose of this check and exit is to aid in debugging a guest that is in all likelihood already doomed. Invalid guest state in PM is extremely limited in normal operation, e.g. it generally only occurs for a few instructions early in BIOS, and any exception at this time is all but guaranteed to be fatal. Non-vectored interrupts, e.g. INIT, SIPI and SMI, can be cleanly handled/emulated, while checking for vectored interrupts, e.g. INTR and NMI, without hitting false positives would add a fair amount of complexity for almost no benefit (getting hit by lightning seems more likely than encountering this specific scenario). Add a WARN_ON_ONCE to vmx_queue_exception() if we try to inject an exception via the VMCS and emulation_required is true. Signed-off-by: Sean Christopherson Signed-off-by: Radim Krčmář --- arch/x86/kvm/vmx.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 5d321506b24b..b2f8a700aeef 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -2797,6 +2797,8 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu) return; } + WARN_ON_ONCE(vmx->emulation_required); + if (kvm_exception_is_soft(nr)) { vmcs_write32(VM_ENTRY_INSTRUCTION_LEN, vmx->vcpu.arch.event_exit_inst_len); @@ -7162,12 +7164,12 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu) goto out; } - if (err != EMULATE_DONE) { - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; - vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION; - vcpu->run->internal.ndata = 0; - return 0; - } + if (err != EMULATE_DONE) + goto emulation_error; + + if (vmx->emulation_required && !vmx->rmode.vm86_active && + vcpu->arch.exception.pending) + goto emulation_error; if (vcpu->arch.halt_request) { vcpu->arch.halt_request = 0; @@ -7183,6 +7185,12 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu) out: return ret; + +emulation_error: + vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR; + vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION; + vcpu->run->internal.ndata = 0; + return 0; } static void grow_ple_window(struct kvm_vcpu *vcpu) -- cgit v1.2.3