From: Roland McGrath Date: Tue, 24 Jun 2008 03:41:12 +0000 (-0700) Subject: x86_64: remove bogus optimization in sysret_signal X-Git-Tag: v2.6.27-rc1~846^2~3 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=15e8f348db372dec21229fda5d52ae6ee7e64666;p=linux-2.6 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 --- diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 8410e26f41..a169225869 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)