[Xen-changelog] [xen stable-4.6] x86/hvm: Perform a user instruction fetch for a FEP in userspace

[patchbot@xxxxxxx]

commit c3b06b0a7523374822e2eec789178444eefc5710
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Sep 12 16:00:30 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 12 16:00:30 2016 +0200

    x86/hvm: Perform a user instruction fetch for a FEP in userspace
    
    This matches hardware behaviour, and prevents erroneous failures when a 
guest
    has SMEP/SMAP active and issues a FEP from userspace.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 0831e99446121636045cf6f616a1991d6ef22071
    master date: 2016-09-08 16:39:46 +0100
---
 xen/arch/x86/hvm/svm/svm.c | 4 +++-
 xen/arch/x86/hvm/vmx/vmx.c | 4 +++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 07ccae3..74aa075 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2131,10 +2131,12 @@ static void svm_vmexit_ud_intercept(struct 
cpu_user_regs *regs)
 
     if ( opt_hvm_fep )
     {
+        uint32_t walk = (ctxt.seg_reg[x86_seg_ss].attr.fields.dpl == 3)
+            ? PFEC_user_mode : 0;
         char sig[5]; /* ud2; .ascii "xen" */
 
         if ( (hvm_fetch_from_guest_virt_nofault(
-                  sig, regs->eip, sizeof(sig), 0) == HVMCOPY_okay) &&
+                  sig, regs->eip, sizeof(sig), walk) == HVMCOPY_okay) &&
              (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) )
         {
             regs->eip += sizeof(sig);
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 698c906..7f96ad6 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2763,10 +2763,12 @@ static void vmx_vmexit_ud_intercept(struct 
cpu_user_regs *regs)
 
     if ( opt_hvm_fep )
     {
+        uint32_t walk = (ctxt.seg_reg[x86_seg_ss].attr.fields.dpl == 3)
+            ? PFEC_user_mode : 0;
         char sig[5]; /* ud2; .ascii "xen" */
 
         if ( (hvm_fetch_from_guest_virt_nofault(
-                  sig, regs->eip, sizeof(sig), 0) == HVMCOPY_okay) &&
+                  sig, regs->eip, sizeof(sig), walk) == HVMCOPY_okay) &&
              (memcmp(sig, "\xf\xbxen", sizeof(sig)) == 0) )
         {
             regs->eip += sizeof(sig);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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