[Xen-changelog] [xen stable-4.10] x86/pv: Hide more EFER bits from PV guests

[patchbot@xxxxxxx]

commit aaf66de7c547e7cbe10d4fb5cc8b8f99238404a8
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri May 18 11:47:37 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri May 18 11:47:37 2018 +0200

    x86/pv: Hide more EFER bits from PV guests
    
    We don't advertise SVM in CPUID so a PV guest shouldn't be under the
    impression that it can use SVM functionality, but despite this, it really
    shouldn't see SVME set when reading EFER.
    
    On Intel processors, 32bit PV guests don't see, and can't use SYSCALL.
    
    Introduce EFER_KNOWN_MASK to whitelist the features Xen knows about, and use
    this to clamp the guests view.
    
    Take the opportunity to reuse the mask to simplify svm_vmcb_isvalid(), and
    change "undefined" to "unknown" in the print message, as there is at least
    EFER.TCE (Translation Cache Extension) defined but unknown to Xen.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 589263031c04e2ba527783b4e04e8df27d364769
    master date: 2018-05-07 11:52:57 +0100
---
 xen/arch/x86/hvm/svm/svmdebug.c |  5 ++---
 xen/arch/x86/pv/emul-priv-op.c  | 11 +++++++++--
 xen/include/asm-x86/msr-index.h |  3 +++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svmdebug.c b/xen/arch/x86/hvm/svm/svmdebug.c
index 89ef2db932..b5b946aa94 100644
--- a/xen/arch/x86/hvm/svm/svmdebug.c
+++ b/xen/arch/x86/hvm/svm/svmdebug.c
@@ -131,9 +131,8 @@ bool svm_vmcb_isvalid(const char *from, const struct 
vmcb_struct *vmcb,
         PRINTF("DR7: bits [63:32] are not zero (%#"PRIx64")\n",
                vmcb_get_dr7(vmcb));
 
-    if ( efer & ~(EFER_SCE | EFER_LME | EFER_LMA | EFER_NX | EFER_SVME |
-                  EFER_LMSLE | EFER_FFXSE) )
-        PRINTF("EFER: undefined bits are not zero (%#"PRIx64")\n", efer);
+    if ( efer & ~EFER_KNOWN_MASK )
+        PRINTF("EFER: unknown bits are not zero (%#"PRIx64")\n", efer);
 
     if ( hvm_efer_valid(v, efer, -1) )
         PRINTF("EFER: %s (%"PRIx64")\n", hvm_efer_valid(v, efer, -1), efer);
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 37627054b1..c281936af0 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -886,9 +886,16 @@ static int read_msr(unsigned int reg, uint64_t *val,
         return X86EMUL_OKAY;
 
     case MSR_EFER:
-        *val = read_efer();
+        /* Hide unknown bits, and unconditionally hide SVME from guests. */
+        *val = read_efer() & EFER_KNOWN_MASK & ~EFER_SVME;
+        /*
+         * Hide the 64-bit features from 32-bit guests.  SCE has
+         * vendor-dependent behaviour.
+         */
         if ( is_pv_32bit_domain(currd) )
-            *val &= ~(EFER_LME | EFER_LMA | EFER_LMSLE);
+            *val &= ~(EFER_LME | EFER_LMA | EFER_LMSLE |
+                      (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL
+                       ? EFER_SCE : 0));
         return X86EMUL_OKAY;
 
     case MSR_K7_FID_VID_CTL:
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index bb6295790c..68fae91567 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-4.10

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