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

[patchbot@xxxxxxx]

commit 589263031c04e2ba527783b4e04e8df27d364769
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Mar 20 19:36:40 2018 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon May 7 11:52:57 2018 +0100

    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>
    Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
---
 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 6c215d19fe..d35e40596b 100644
--- a/xen/arch/x86/hvm/svm/svmdebug.c
+++ b/xen/arch/x86/hvm/svm/svmdebug.c
@@ -133,9 +133,8 @@ 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 15f42b34ce..ce2ec76cde 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -867,9 +867,16 @@ 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 c9f44ebdb3..6d94d65575 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#master

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