From 7f9ad1dfa3c768d1116c2dbacd7a09f9a871534e Mon Sep 17 00:00:00 2001 From: Liran Alon Date: Sat, 17 Nov 2018 14:05:06 +0200 Subject: [PATCH] KVM: nVMX: Fix kernel info-leak when enabling KVM_CAP_HYPERV_ENLIGHTENED_VMCS more than once Consider the case that userspace enables KVM_CAP_HYPERV_ENLIGHTENED_VMCS twice: 1) kvm_vcpu_ioctl_enable_cap() is called to enable KVM_CAP_HYPERV_ENLIGHTENED_VMCS which calls nested_enable_evmcs(). 2) nested_enable_evmcs() sets enlightened_vmcs_enabled to true and fills vmcs_version which is then copied to userspace. 3) kvm_vcpu_ioctl_enable_cap() is called again to enable KVM_CAP_HYPERV_ENLIGHTENED_VMCS which calls nested_enable_evmcs(). 4) This time nested_enable_evmcs() just returns 0 as enlightened_vmcs_enabled is already true. *Without filling vmcs_version*. 5) kvm_vcpu_ioctl_enable_cap() continues as usual and copies *uninitialized* vmcs_version to userspace which leads to kernel info-leak. Fix this issue by simply changing nested_enable_evmcs() to always fill vmcs_version output argument. Even when enlightened_vmcs_enabled is already set to true. Note that SVM's nested_enable_evmcs() should not be modified because it always returns a non-zero value (-ENODEV) which results in kvm_vcpu_ioctl_enable_cap() skipping the copy of vmcs_version to userspace (as it should). Fixes: 57b119da3594 ("KVM: nVMX: add KVM_CAP_HYPERV_ENLIGHTENED_VMCS capability") Reported-by: syzbot+cfbc368e283d381f8cef@syzkaller.appspotmail.com Reviewed-by: Krish Sadhukhan Reviewed-by: Vitaly Kuznetsov Signed-off-by: Liran Alon Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index be6f13f1c25f..065f1df74000 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -1611,12 +1611,6 @@ static int nested_enable_evmcs(struct kvm_vcpu *vcpu, { struct vcpu_vmx *vmx = to_vmx(vcpu); - /* We don't support disabling the feature for simplicity. */ - if (vmx->nested.enlightened_vmcs_enabled) - return 0; - - vmx->nested.enlightened_vmcs_enabled = true; - /* * vmcs_version represents the range of supported Enlightened VMCS * versions: lower 8 bits is the minimal version, higher 8 bits is the @@ -1626,6 +1620,12 @@ static int nested_enable_evmcs(struct kvm_vcpu *vcpu, if (vmcs_version) *vmcs_version = (KVM_EVMCS_VERSION << 8) | 1; + /* We don't support disabling the feature for simplicity. */ + if (vmx->nested.enlightened_vmcs_enabled) + return 0; + + vmx->nested.enlightened_vmcs_enabled = true; + vmx->nested.msrs.pinbased_ctls_high &= ~EVMCS1_UNSUPPORTED_PINCTRL; vmx->nested.msrs.entry_ctls_high &= ~EVMCS1_UNSUPPORTED_VMENTRY_CTRL; vmx->nested.msrs.exit_ctls_high &= ~EVMCS1_UNSUPPORTED_VMEXIT_CTRL;