Commit 15e8f348 authored Jun 23, 2008 by Roland McGrath

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>

parent 20b7997e

arch/x86/kernel/entry_64.S

+1 −5

Original line number	Diff line number	Diff line
		@@ -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)