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authorOliver Upton <oupton@google.com>2020-08-18 15:24:28 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2020-10-21 17:36:32 -0400
commit66570e966dd9cb4fd57811d0056c6472a14a2c41 (patch)
tree06172486c1b55c545ea71bc0cd23c288c7b19fd1 /Documentation/virt/kvm
parent210dfd93ea3dc63e8c21b75ddd909447341f6382 (diff)
downloadlinux-66570e966dd9cb4fd57811d0056c6472a14a2c41.tar.bz2
kvm: x86: only provide PV features if enabled in guest's CPUID
KVM unconditionally provides PV features to the guest, regardless of the configured CPUID. An unwitting guest that doesn't check KVM_CPUID_FEATURES before use could access paravirt features that userspace did not intend to provide. Fix this by checking the guest's CPUID before performing any paravirtual operations. Introduce a capability, KVM_CAP_ENFORCE_PV_FEATURE_CPUID, to gate the aforementioned enforcement. Migrating a VM from a host w/o this patch to a host with this patch could silently change the ABI exposed to the guest, warranting that we default to the old behavior and opt-in for the new one. Reviewed-by: Jim Mattson <jmattson@google.com> Reviewed-by: Peter Shier <pshier@google.com> Signed-off-by: Oliver Upton <oupton@google.com> Change-Id: I202a0926f65035b872bfe8ad15307c026de59a98 Message-Id: <20200818152429.1923996-4-oupton@google.com> Reviewed-by: Wanpeng Li <wanpengli@tencent.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt/kvm')
-rw-r--r--Documentation/virt/kvm/api.rst11
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 9ece9a827a58..76317221d29f 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6380,3 +6380,14 @@ ranges that KVM should reject access to.
In combination with KVM_CAP_X86_USER_SPACE_MSR, this allows user space to
trap and emulate MSRs that are outside of the scope of KVM as well as
limit the attack surface on KVM's MSR emulation code.
+
+
+8.26 KVM_CAP_ENFORCE_PV_CPUID
+-----------------------------
+
+Architectures: x86
+
+When enabled, KVM will disable paravirtual features provided to the
+guest according to the bits in the KVM_CPUID_FEATURES CPUID leaf
+(0x40000001). Otherwise, a guest may use the paravirtual features
+regardless of what has actually been exposed through the CPUID leaf.