From 2732be90235347a3be4babdc9f88a1ea93970b0b Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 3 Feb 2021 16:01:07 -0800 Subject: [PATCH] KVM: nSVM: Don't strip host's C-bit from guest's CR3 when reading PDPTRs Don't clear the SME C-bit when reading a guest PDPTR, as the GPA (CR3) is in the guest domain. Barring a bizarre paravirtual use case, this is likely a benign bug. SME is not emulated by KVM, loading SEV guest PDPTRs is doomed as KVM can't use the correct key to read guest memory, and setting guest MAXPHYADDR higher than the host, i.e. overlapping the C-bit, would cause faults in the guest. Note, for SEV guests, stripping the C-bit is technically aligned with CPU behavior, but for KVM it's the greater of two evils. Because KVM doesn't have access to the guest's encryption key, ignoring the C-bit would at best result in KVM reading garbage. By keeping the C-bit, KVM will fail its read (unless userspace creates a memslot with the C-bit set). The guest will still undoubtedly die, as KVM will use '0' for the PDPTR value, but that's preferable to interpreting encrypted data as a PDPTR. Fixes: d0ec49d4de90 ("kvm/x86/svm: Support Secure Memory Encryption within KVM") Cc: Tom Lendacky Cc: Brijesh Singh Signed-off-by: Sean Christopherson Message-Id: <20210204000117.3303214-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/nested.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index d679130d209b..69188897cae2 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -58,7 +58,7 @@ static u64 nested_svm_get_tdp_pdptr(struct kvm_vcpu *vcpu, int index) u64 pdpte; int ret; - ret = kvm_vcpu_read_guest_page(vcpu, gpa_to_gfn(__sme_clr(cr3)), &pdpte, + ret = kvm_vcpu_read_guest_page(vcpu, gpa_to_gfn(cr3), &pdpte, offset_in_page(cr3) + index * 8, 8); if (ret) return 0;