Hi!
From: Sean Christopherson sean.j.christopherson@intel.com
commit 11988499e62b310f3bf6f6d0a807a06d3f9ccc96 upstream.
KVM allows userspace to violate consistency checks related to the guest's CPUID model to some degree. Generally speaking, userspace has carte blanche when it comes to guest state so long as jamming invalid state won't negatively affect the host.
Currently this is seems to be a non-issue as most of the interesting EFER checks are missing, e.g. NX and LME, but those will be added shortly. Proactively exempt userspace from the CPUID checks so as not to break userspace.
Note, the efer_reserved_bits check still applies to userspace writes as that mask reflects the host's capabilities, e.g. KVM shouldn't allow a guest to run with NX=1 if it has been disabled in the host.
arch/x86/kvm/x86.c | 37 ++++++++++++++++++++++++------------- 1 file changed, 24 insertions(+), 13 deletions(-)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c -static int set_efer(struct kvm_vcpu *vcpu, u64 efer) +static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info) { u64 old_efer = vcpu->arch.efer;
- u64 efer = msr_info->data;
- if (!kvm_valid_efer(vcpu, efer))
return 1;
- if (efer & efer_reserved_bits)
return false;
- if (is_paging(vcpu)
&& (vcpu->arch.efer & EFER_LME) != (efer & EFER_LME))return 1;
- if (!msr_info->host_initiated) {
if (!__kvm_valid_efer(vcpu, efer))return 1;
We have "return false" in function returning int. Plus calling convention here seems to be "nonzero on error" so it should be returning 1?
@@ -2356,7 +2367,7 @@ int kvm_set_msr_common(struct kvm_vcpu * vcpu->arch.arch_capabilities = data; break; case MSR_EFER:
return set_efer(vcpu, data);
return set_efer(vcpu, msr_info);