[libvirt] [PATCH 2/2] cpu: define the 'virt-ssbd' CPUID feature bit (CVE-2018-3639)

Daniel P. Berrangé berrange at redhat.com
Mon May 21 22:05:08 UTC 2018

Some AMD processors only support a non-architectural means of
enabling Speculative Store Bypass Disable. To allow simplified
handling in virtual environments, hypervisors will expose an
architectural definition through CPUID bit 0x80000008_EBX[25].
This needs to be exposed to guest OS running on AMD x86 hosts to
allow them to protect against CVE-2018-3639.

Note that since this CPUID bit won't be present in the host CPUID
results on physical hosts, it will not be enabled automatically
in guests configured with "host-model" CPU unless using QEMU
version >= 2.9.0. Thus for older versions of QEMU, this feature
must be manually enabled using policy=force. Guests using the
"host-passthrough" CPU mode do not need special handling.

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
 src/cpu/cpu_map.xml | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/cpu/cpu_map.xml b/src/cpu/cpu_map.xml
index 245aec3309..96daa0f9af 100644
--- a/src/cpu/cpu_map.xml
+++ b/src/cpu/cpu_map.xml
@@ -433,6 +433,9 @@
     <feature name='ibpb'>
       <cpuid eax_in='0x80000008' ebx='0x00001000'/>
+    <feature name='virt-ssbd'>
+      <cpuid eax_in='0x80000008' ebx='0x02000000'/>
+    </feature>
     <!-- models -->
     <model name='486'>

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