Commit-ID: 29a2e2836ff9ea65a603c89df217f4198973a74f
Gitweb: http://git.kernel.org/tip/29a2e2836ff9ea65a603c89df217f4198973a74f
Author: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>
AuthorDate: Thu, 22 Mar 2012 21:39:25 +0100
Committer: H. Peter Anvin <hpa@xxxxxxxxx>
CommitDate: Thu, 22 Mar 2012 13:50:25 -0700
x86-32: Fix endless loop when processing signals for kernel tasks
The problem occurs on !CONFIG_VM86 kernels [1] when a kernel-mode task
returns from a system call with a pending signal.
A real-life scenario is a child of 'khelper' returning from a failed
kernel_execve() in ____call_usermodehelper() [ kernel/kmod.c ].
kernel_execve() fails due to a pending SIGKILL, which is the result of
"kill -9 -1" (at least, busybox's init does it upon reboot).
The loop is as follows:
* syscall_exit_work:
- work_pending: // start_of_the_loop
- work_notify_sig:
- do_notify_resume()
- do_signal()
- if (!user_mode(regs)) return;
- resume_userspace // TIF_SIGPENDING is still set
- work_pending // so we call work_pending => goto
// start_of_the_loop
More information can be found in another LKML thread:
http://www.serverphorums.com/read.php?12,457826
[1] the problem was also seen on MIPS.
Signed-off-by: Dmitry Adamushko <dmitry.adamushko@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1332448765.2299.68.camel@dimm
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
---
arch/x86/kernel/entry_32.S | 17 ++++++++++-------
1 files changed, 10 insertions(+), 7 deletions(-)
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 79d97e6..7b784f4 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -98,12 +98,6 @@
#endif
.endm
-#ifdef CONFIG_VM86
-#define resume_userspace_sig check_userspace
-#else
-#define resume_userspace_sig resume_userspace
-#endif
-
/*
* User gs save/restore
*
@@ -327,10 +321,19 @@ ret_from_exception:
preempt_stop(CLBR_ANY)
ret_from_intr:
GET_THREAD_INFO(%ebp)
-check_userspace:
+resume_userspace_sig:
+#ifdef CONFIG_VM86
movl PT_EFLAGS(%esp), %eax # mix EFLAGS and CS
movb PT_CS(%esp), %al
andl $(X86_EFLAGS_VM | SEGMENT_RPL_MASK), %eax
+#else
+ /*
+ * We can be coming here from a syscall done in the kernel space,
+ * e.g. a failed kernel_execve().
+ */
+ movl PT_CS(%esp), %eax
+ andl $SEGMENT_RPL_MASK, %eax
+#endif
cmpl $USER_RPL, %eax
jb resume_kernel # not returning to v8086 or userspace
--
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