[xen stable-4.13] x86/pv: Don't deliver #GP for a SYSENTER with NT set

[patchbot@xxxxxxx]

commit 055a5d540b8a9f40be71fd52eacb39f0b3acf7b7
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Oct 20 14:54:12 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 20 14:54:12 2020 +0200

    x86/pv: Don't deliver #GP for a SYSENTER with NT set
    
    It is a matter of guest kernel policy what to do with offending userspace, 
and
    terminating said userspace may not be the action chosen.
    
    Linux explicitly tolerates this case.
    
    Reported-by: Andy Lutomirski <luto@xxxxxxxxxx>
    Fixes: fdac951560 ("x86: clear EFLAGS.NT in SYSENTER entry path")
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 61d4a04349895edc5a5868274b906ba61ef24f47
    master date: 2020-09-24 21:02:35 +0100
---
 xen/arch/x86/x86_64/entry.S | 1 -
 1 file changed, 1 deletion(-)

diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 7850546749..6a5f8aaec3 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -296,7 +296,6 @@ UNLIKELY_START(nz, sysenter_nt_set)
         pushfq
         andl  $~X86_EFLAGS_NT,(%rsp)
         popfq
-        xorl  %eax,%eax
 UNLIKELY_END(sysenter_nt_set)
         testq %rax,%rax
         leal  (,%rcx,TBF_INTERRUPT),%ecx
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.13