[Xen-changelog] [xen stable-4.9] x86/hvm: Disallow unknown MSR_EFER bits

[patchbot@xxxxxxx]

commit a894c9dcbdda6d0d187db71d69ca3d48e7ea8a16
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jul 30 11:56:57 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jul 30 11:56:57 2018 +0200

    x86/hvm: Disallow unknown MSR_EFER bits
    
    It turns out that nothing ever prevented HVM guests from trying to set 
unknown
    EFER bits.  Generally, this results in a vmentry failure.
    
    For Intel hardware, all implemented bits are covered by the checks.
    
    For AMD hardware, the only EFER bit which isn't covered by the checks is TCE
    (which AFAICT is specific to AMD Fam15/16 hardware).  We never advertise TCE
    in CPUID, but it isn't a security problem to have TCE unexpected enabled in
    guest context.
    
    Disallow the setting of bits outside of the EFER_KNOWN_MASK, which prevents
    any vmentry failures for guests, yielding #GP instead.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: ef0269c6215d642a709866f04ba1a1f9f13f3614
    master date: 2018-07-24 11:25:53 +0100
---
 xen/arch/x86/hvm/hvm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index d6fe84d229..9f2ecbb9c6 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -889,6 +889,9 @@ const char *hvm_efer_valid(const struct vcpu *v, uint64_t 
value,
     else
         p = &host_policy;
 
+    if ( value & ~EFER_KNOWN_MASK )
+        return "Unknown bits set";
+
     if ( (value & EFER_SCE) && !p->extd.syscall )
         return "SCE without feature";
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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