kprobes/x86-32: Move irq-exit functions to kprobes section

Move irq-exit functions to .kprobes.text section to protect against
kprobes recursion.

When I ran kprobe stress test on x86-32, I found below symbols
cause unrecoverable recursive probing:

	ret_from_exception
	ret_from_intr
	check_userspace
	restore_all
	restore_all_notrace
	restore_nocheck
	irq_return

And also, I found some interrupt/exception entry points that
cause similar problems.

This patch moves those symbols (including their container functions)
to .kprobes.text section to prevent any kprobes probing.
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Jim Keniston <jkenisto@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <20090908164755.24050.81182.stgit@dhcp-100-2-132.bos.redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

arch/x86/kernel/entry_32.S

@@ -333,6 +333,10 @@ ENTRY(ret_from_fork)
 	CFI_ENDPROC
 END(ret_from_fork)
 
+/*
+ * Interrupt exit functions should be protected against kprobes
+ */
+	.pushsection .kprobes.text, "ax"
 /*
  * Return to user mode is not as complex as all this looks,
  * but we want the default path for a system call return to
@@ -383,6 +387,10 @@ need_resched:
 END(resume_kernel)
 #endif
 	CFI_ENDPROC
+/*
+ * End of kprobes section
+ */
+	.popsection
 
 /* SYSENTER_RETURN points to after the "sysenter" instruction in
    the vsyscall page.  See vsyscall-sysentry.S, which defines the symbol.  */
@@ -513,6 +521,10 @@ sysexit_audit:
 	PTGS_TO_GS_EX
 ENDPROC(ia32_sysenter_target)
 
+/*
+ * syscall stub including irq exit should be protected against kprobes
+ */
+	.pushsection .kprobes.text, "ax"
 	# system call handler stub
 ENTRY(system_call)
 	RING0_INT_FRAME			# can't unwind into user space anyway
@@ -705,6 +717,10 @@ syscall_badsys:
 	jmp resume_userspace
 END(syscall_badsys)
 	CFI_ENDPROC
+/*
+ * End of kprobes section
+ */
+	.popsection
 
 /*
  * System calls that need a pt_regs pointer.
@@ -814,6 +830,10 @@ common_interrupt:
 ENDPROC(common_interrupt)
 	CFI_ENDPROC
 
+/*
+ *  Irq entries should be protected against kprobes
+ */
+	.pushsection .kprobes.text, "ax"
 #define BUILD_INTERRUPT3(name, nr, fn)	\
 ENTRY(name)				\
 	RING0_INT_FRAME;		\
@@ -980,6 +1000,10 @@ ENTRY(spurious_interrupt_bug)
 	jmp error_code
 	CFI_ENDPROC
 END(spurious_interrupt_bug)
+/*
+ * End of kprobes section
+ */
+	.popsection
 
 ENTRY(kernel_thread_helper)
 	pushl $0		# fake return address for unwinder

kernel/kprobes.c

@@ -91,6 +91,8 @@ static spinlock_t *kretprobe_table_lock_ptr(unsigned long hash)
 static struct kprobe_blackpoint kprobe_blacklist[] = {
 	{"preempt_schedule",},
 	{"native_get_debugreg",},
+	{"irq_entries_start",},
+	{"common_interrupt",},
 	{NULL}    /* Terminator */
 };