From 023cfa6fc200fc179dbf8e1857cc7140fa1466f9 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 13 Apr 2023 16:19:14 -0700 Subject: [PATCH] KVM: VMX: Use proper accessor to read guest CR4 in handle_desc() Use kvm_is_cr4_bit_set() to read guest CR4.UMIP when sanity checking that a descriptor table VM-Exit occurs if and only if guest.CR4.UMIP=1. UMIP can't be guest-owned, i.e. using kvm_read_cr4_bits() to decache guest- owned bits isn't strictly necessary, but eliminating raw reads of vcpu->arch.cr4 is desirable as it makes it easy to visually audit KVM for correctness. Opportunistically add a compile-time assertion that UMIP isn't guest-owned as letting the guest own UMIP isn't compatible with emulation (or any CR4 bit that is emulated by KVM). Opportunistically change the WARN_ON() to a ONCE variant. When the WARN fires, it fires _a lot_, and spamming the kernel logs ends up doing more harm than whatever led to KVM's unnecessary emulation. Reported-by: Robert Hoo Link: https://lore.kernel.org/all/20230310125718.1442088-4-robert.hu@intel.com Link: https://lore.kernel.org/r/20230413231914.1482782-3-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/vmx/vmx.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 98f966635c88..7ecab2118106 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -5402,7 +5402,13 @@ static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val) static int handle_desc(struct kvm_vcpu *vcpu) { - WARN_ON(!(vcpu->arch.cr4 & X86_CR4_UMIP)); + /* + * UMIP emulation relies on intercepting writes to CR4.UMIP, i.e. this + * and other code needs to be updated if UMIP can be guest owned. + */ + BUILD_BUG_ON(KVM_POSSIBLE_CR4_GUEST_BITS & X86_CR4_UMIP); + + WARN_ON_ONCE(!kvm_is_cr4_bit_set(vcpu, X86_CR4_UMIP)); return kvm_emulate_instruction(vcpu, 0); } -- 2.20.1