[Xen-changelog] [xen stable-4.2] x86/HVM: refine SMEP test in HVM_CR4_GUEST_RESERVED_BITS()

[patchbot@xxxxxxx]

commit 26d074fdbf3da16e38bd7898d29ac8480e71e5d7
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 24 10:17:45 2014 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 24 10:17:45 2014 +0200

    x86/HVM: refine SMEP test in HVM_CR4_GUEST_RESERVED_BITS()
    
    Andrew validly points out that the use of the macro on the restore path
    can't rely on the CPUID bits for the guest already being in place (as
    their setting by the tool stack in turn requires the other restore
    operations already having taken place). And even worse, using
    hvm_cpuid() is invalid here because that function assumes to be used in
    the context of the vCPU in question.
    
    Reverting to the behavior prior to the change from checking
    cpu_has_sm?p to hvm_vcpu_has_sm?p() would break the other (non-restore)
    use of the macro. So let's revert to the prior behavior only for the
    restore path, by adding a respective second parameter to the macro.
    
    Obviously the two cpu_has_* uses in the macro should really also be
    converted to hvm_cpuid() based checks at least for the non-restore
    path.
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Tested-by: David Vrabel <david.vrabel@xxxxxxxxxx>
    master commit: 584287380baf81e5acdd9dc7dfc7ffccd1e9a856
    master date: 2014-06-10 13:12:05 +0200
---
 xen/arch/x86/hvm/hvm.c        |    4 ++--
 xen/include/asm-x86/hvm/hvm.h |   18 ++++++++++++------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 68531ab..7d4b0b3 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -751,7 +751,7 @@ static int hvm_load_cpu_ctxt(struct domain *d, 
hvm_domain_context_t *h)
         return -EINVAL;
     }
 
-    if ( ctxt.cr4 & HVM_CR4_GUEST_RESERVED_BITS(v) )
+    if ( ctxt.cr4 & HVM_CR4_GUEST_RESERVED_BITS(v, 1) )
     {
         printk(XENLOG_G_ERR "HVM%d restore: bad CR4 %#" PRIx64 "\n",
                d->domain_id, ctxt.cr4);
@@ -1842,7 +1842,7 @@ int hvm_set_cr4(unsigned long value)
     struct vcpu *v = current;
     unsigned long old_cr;
 
-    if ( value & HVM_CR4_GUEST_RESERVED_BITS(v) )
+    if ( value & HVM_CR4_GUEST_RESERVED_BITS(v, 0) )
     {
         HVM_DBG_LOG(DBG_LEVEL_1,
                     "Guest attempts to set reserved bit in CR4: %lx",
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index 902f224..d6bb844 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -365,18 +365,24 @@ static inline bool_t hvm_vcpu_has_smep(void)
     (X86_CR4_VMXE | X86_CR4_PAE | X86_CR4_MCE))
 
 /* These bits in CR4 cannot be set by the guest. */
-#define HVM_CR4_GUEST_RESERVED_BITS(_v)                 \
+#define HVM_CR4_GUEST_RESERVED_BITS(v, restore) ({      \
+    const struct vcpu *_v = (v);                        \
+    bool_t _restore = !!(restore);                      \
+    ASSERT((_restore) || _v == current);                \
     (~((unsigned long)                                  \
        (X86_CR4_VME | X86_CR4_PVI | X86_CR4_TSD |       \
         X86_CR4_DE  | X86_CR4_PSE | X86_CR4_PAE |       \
         X86_CR4_MCE | X86_CR4_PGE | X86_CR4_PCE |       \
         X86_CR4_OSFXSR | X86_CR4_OSXMMEXCPT |           \
-        (hvm_vcpu_has_smep() ? X86_CR4_SMEP : 0) |      \
+        (((_restore) ? cpu_has_smep :                   \
+                       hvm_vcpu_has_smep()) ?           \
+         X86_CR4_SMEP : 0) |                            \
         (cpu_has_fsgsbase ? X86_CR4_FSGSBASE : 0) |     \
-        ((nestedhvm_enabled((_v)->domain) && cpu_has_vmx)\
-                      ? X86_CR4_VMXE : 0)  |             \
-        (cpu_has_pcid ? X86_CR4_PCIDE : 0) |             \
-        (cpu_has_xsave ? X86_CR4_OSXSAVE : 0))))
+        ((nestedhvm_enabled(_v->domain) && cpu_has_vmx) \
+                      ? X86_CR4_VMXE : 0)  |            \
+        (cpu_has_pcid ? X86_CR4_PCIDE : 0) |            \
+        (cpu_has_xsave ? X86_CR4_OSXSAVE : 0))));       \
+})
 
 /* These exceptions must always be intercepted. */
 #define HVM_TRAP_MASK ((1U << TRAP_machine_check) | (1U << TRAP_invalid_op))
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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