Commit 15e8f348 authored by Roland McGrath's avatar Roland McGrath
Browse files

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: default avatarRoland McGrath <roland@redhat.com>
parent 20b7997e
......@@ -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)
......
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