[Xen-changelog] [xen stable-4.5] nested vmx: Validate host VMX MSRs before accessing them

[patchbot@xxxxxxx]

commit b1f4e86aa3bd224bde62f18cf51381e6fe731a2f
Author:     Euan Harris <euan.harris@xxxxxxxxxx>
AuthorDate: Fri Aug 5 13:50:47 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Aug 5 13:50:47 2016 +0200

    nested vmx: Validate host VMX MSRs before accessing them
    
    Some VMX MSRs may not exist on certain processor models, or may
    be disabled because of configuration settings.   It is only safe to
    access these MSRs if configuration flags in other MSRs are set.  These
    prerequisites are listed in the Intel 64 and IA-32 Architectures
    Software Developerâ??s Manual, Vol 3, Appendix A.
    
    nvmx_msr_read_intercept() does not check the prerequisites before
    accessing MSR_IA32_VMX_PROCBASED_CTLS2, MSR_IA32_VMX_EPT_VPID_CAP,
    MSR_IA32_VMX_VMFUNC on the host.   Accessing these MSRs from a nested
    VMX guest running on a host which does not support them will cause
    Xen to crash with a GPF.
    
    Signed-off-by: Euan Harris <euan.harris@xxxxxxxxxx>
    Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 5e02972646132ad98c365ebfcfcb43b40a0dde36
    master date: 2016-06-13 12:44:32 +0100
---
 xen/arch/x86/hvm/vmx/vvmx.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
index 41e5dc3..d1c08c4 100644
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -1864,11 +1864,22 @@ int nvmx_msr_read_intercept(unsigned int msr, u64 
*msr_content)
         return 0;
 
     /*
-     * Those MSRs are available only when bit 55 of
-     * MSR_IA32_VMX_BASIC is set.
+     * These MSRs are only available when flags in other MSRs are set.
+     * These prerequisites are listed in the Intel 64 and IA-32
+     * Architectures Software Developerâ??s Manual, Vol 3, Appendix A.
      */
     switch ( msr )
     {
+    case MSR_IA32_VMX_PROCBASED_CTLS2:
+        if ( !cpu_has_vmx_secondary_exec_control )
+            return 0;
+        break;
+
+    case MSR_IA32_VMX_EPT_VPID_CAP:
+        if ( !(cpu_has_vmx_ept || cpu_has_vmx_vpid) )
+            return 0;
+        break;
+
     case MSR_IA32_VMX_TRUE_PINBASED_CTLS:
     case MSR_IA32_VMX_TRUE_PROCBASED_CTLS:
     case MSR_IA32_VMX_TRUE_EXIT_CTLS:
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.5

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