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authorRoland McGrath <roland@redhat.com>2008-06-24 03:41:12 (GMT)
committerRoland McGrath <roland@redhat.com>2008-07-24 00:43:36 (GMT)
commit15e8f348db372dec21229fda5d52ae6ee7e64666 (patch)
tree73afc044ef5b4e29a893e98afee2fe794938aeb3
parent20b7997e8abdf338dcc27fb4f1333c4973a7f113 (diff)
downloadlinux-15e8f348db372dec21229fda5d52ae6ee7e64666.tar.xz
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>
-rw-r--r--arch/x86/kernel/entry_64.S6
1 files changed, 1 insertions, 5 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 8410e26..a169225 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)