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

[patchbot@xxxxxxx]

commit 61d4a04349895edc5a5868274b906ba61ef24f47
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Jun 26 14:56:23 2020 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Sep 24 21:02:35 2020 +0100

    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>
---
 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 71a00e846b..44a110b9c8 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -313,7 +313,6 @@ 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#staging