[PATCH -tip 1/2] [BUGFIX] kprobes/x86: Prohibit probing on debug_stack_*

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

Prohibit probing on debug_stack_reset and debug_stack_set_zero.
Since the both functions are called from TRACE_IRQS_ON/OFF_DEBUG
macros which run in int3 ist entry, probing it may cause a soft
lockup.

This happens when the kernel built with CONFIG_DYNAMIC_FTRACE=y
and CONFIG_TRACE_IRQFLAGS=y.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
---
 arch/x86/kernel/cpu/common.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 35e28b0..8712a1a 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -11,6 +11,7 @@
 #include <linux/kgdb.h>
 #include <linux/smp.h>
 #include <linux/io.h>
+#include <linux/kprobes.h>
 
 #include <asm/stackprotector.h>
 #include <asm/perf_event.h>
@@ -1158,7 +1159,7 @@ DEFINE_PER_CPU(struct orig_ist, orig_ist);
 static DEFINE_PER_CPU(unsigned long, debug_stack_addr);
 DEFINE_PER_CPU(int, debug_stack_usage);
 
-int is_debug_stack(unsigned long addr)
+int __kprobes is_debug_stack(unsigned long addr)
 {
 	return __get_cpu_var(debug_stack_usage) ||
 		(addr <= __get_cpu_var(debug_stack_addr) &&
@@ -1167,13 +1168,13 @@ int is_debug_stack(unsigned long addr)
 
 DEFINE_PER_CPU(u32, debug_idt_ctr);
 
-void debug_stack_set_zero(void)
+void __kprobes debug_stack_set_zero(void)
 {
 	this_cpu_inc(debug_idt_ctr);
 	load_current_idt();
 }
 
-void debug_stack_reset(void)
+void __kprobes debug_stack_reset(void)
 {
 	if (WARN_ON(!this_cpu_read(debug_idt_ctr)))
 		return;