[Xen-changelog] [xen stable-4.7] x86/hvm: Perform a user instruction fetch for a FEP in userspace

[patchbot@xxxxxxx]

commit 129099ba0c2407c32cd7f02011bdf98b8d7cfc0d
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Sep 12 15:56:15 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 12 15:56:15 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/hvm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 40665f5..39ffbf0 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3890,6 +3890,8 @@ void hvm_ud_intercept(struct cpu_user_regs *regs)
     {
         struct vcpu *cur = current;
         struct segment_register cs;
+        uint32_t walk = (ctxt.seg_reg[x86_seg_ss].attr.fields.dpl == 3)
+            ? PFEC_user_mode : 0;
         unsigned long addr;
         char sig[5]; /* ud2; .ascii "xen" */
 
@@ -3900,7 +3902,7 @@ void hvm_ud_intercept(struct cpu_user_regs *regs)
                                          cs.attr.fields.l) ? 64 :
                                         cs.attr.fields.db ? 32 : 16, &addr) &&
              (hvm_fetch_from_guest_virt_nofault(sig, addr, sizeof(sig),
-                                                0) == HVMCOPY_okay) &&
+                                                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-4.7

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