[Xen-changelog] [xen stable-4.8] x86/hvm: Disallow unknown MSR_EFER bits

[patchbot@xxxxxxx]

commit b149b06b1eb5fdc11ef2dfe0af9ce41fc119b5ab
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jul 30 12:10:18 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jul 30 12:10:18 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 +++
 xen/include/asm-x86/msr-index.h | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 298d5ed0c8..56823bd616 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -935,6 +935,9 @@ const char *hvm_efer_valid(const struct vcpu *v, uint64_t 
value,
 {
     unsigned int ext1_ecx = 0, ext1_edx = 0;
 
+    if ( value & ~EFER_KNOWN_MASK )
+        return "Unknown bits set";
+
     if ( cr0_pg < 0 && !is_hardware_domain(v->domain) )
     {
         unsigned int level;
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index 9969504fe1..e7b0be5483 100644
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -31,6 +31,9 @@
 #define EFER_LMSLE             (1<<_EFER_LMSLE)
 #define EFER_FFXSE             (1<<_EFER_FFXSE)
 
+#define EFER_KNOWN_MASK                (EFER_SCE | EFER_LME | EFER_LMA | 
EFER_NX | \
+                                EFER_SVME | EFER_LMSLE | EFER_FFXSE)
+
 /* Speculation Controls. */
 #define MSR_SPEC_CTRL                  0x00000048
 #define SPEC_CTRL_IBRS                 (_AC(1, ULL) << 0)
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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