x86/spectre_v2: Don't check microcode versions when running under hypervisors

commit 36268223c1e9981d6cfc33aff8520b3bde4b8114 upstream.

As:

 1) It's known that hypervisors lie about the environment anyhow (host
    mismatch)

 2) Even if the hypervisor (Xen, KVM, VMWare, etc) provided a valid
    "correct" value, it all gets to be very murky when migration happens
    (do you provide the "new" microcode of the machine?).

And in reality the cloud vendors are the ones that should make sure that
the microcode that is running is correct and we should just sing lalalala
and trust them.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: kvm <kvm@vger.kernel.org>
Cc: Krčmář <rkrcmar@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180226213019.GE9497@char.us.oracle.com
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 4653204d49b7bdf142464ab7f2a56474c279f6a1..aa3d005ad648c5d1323a43e2d2693331c28700a7 100644 (file)
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -68,6 +68,13 @@ static bool bad_spectre_microcode(struct cpuinfo_x86 *c)
 {
        int i;
 
+       /*
+        * We know that the hypervisor lie to us on the microcode version so
+        * we may as well hope that it is running the correct version.
+        */
+       if (cpu_has(c, X86_FEATURE_HYPERVISOR))
+               return false;
+
        for (i = 0; i < ARRAY_SIZE(spectre_bad_microcodes); i++) {
                if (c->x86_model == spectre_bad_microcodes[i].model &&
                    c->x86_mask == spectre_bad_microcodes[i].stepping)