x86_64: remove bogus optimization in sysret_signal

This short-circuit path in sysret_signal looks wrong to me.
AFAICT, in practice the branch is never taken--and if it were,
it would go wrong.  To wit, try loading a module whose init
function does set_thread_flag(TIF_IRET), and see insmod crash
(presumably with a wrong user stack pointer).

This is because the FIXUP_TOP_OF_STACK work hasn't been done yet
when we jump around the call to ptregscall_common and get to
int_with_check--where it expects the user RSP,SS,CS and EFLAGS to
have been stored by FIXUP_TOP_OF_STACK.

I don't think it's normally possible to get to sysret_signal with no
_TIF_DO_NOTIFY_MASK bits set anyway, so these two instructions are
already superfluous.  If it ever did happen, it is harmless to call
do_notify_resume with nothing for it to do.

Signed-off-by: Roland McGrath <roland@redhat.com>

1 files changed, 1 insertions, 5 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 8410e26f4183..a169225869cc 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -402,16 +402,12 @@ sysret_careful:
 sysret_signal:
         TRACE_IRQS_ON
         ENABLE_INTERRUPTS(CLBR_NONE)
-        testl $_TIF_DO_NOTIFY_MASK,%edx
-        jz    1f
-
-        /* Really a signal */
         /* edx: work flags (arg3) */
         leaq do_notify_resume(%rip),%rax
         leaq -ARGOFFSET(%rsp),%rdi # &pt_regs -> arg1
         xorl %esi,%esi # oldset -> arg2
         call ptregscall_common
-1:      movl $_TIF_WORK_MASK,%edi
+        movl $_TIF_WORK_MASK,%edi
         /* Use IRET because user could have changed frame. This
            works because ptregscall_common has called FIXUP_TOP_OF_STACK. */
         DISABLE_INTERRUPTS(CLBR_NONE)