[PATCH -tip v2 2/3] [BUGFIX] kprobes/x86: Prohibit probing ondebug_stack_*

[Masami Hiramatsu]

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@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: Seiji Aguchi <seiji.aguchi@xxxxxxx>
---
 arch/x86/kernel/cpu/common.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 1789b06..928a4fd 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1157,7 +1157,7 @@ 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 nokprobe is_debug_stack(unsigned long addr)
 {
 	return __get_cpu_var(debug_stack_usage) ||
 		(addr <= __get_cpu_var(debug_stack_addr) &&
@@ -1166,13 +1166,13 @@ int is_debug_stack(unsigned long addr)
 
 DEFINE_PER_CPU(u32, debug_idt_ctr);
 
-void debug_stack_set_zero(void)
+void nokprobe debug_stack_set_zero(void)
 {
 	this_cpu_inc(debug_idt_ctr);
 	load_current_idt();
 }
 
-void debug_stack_reset(void)
+void nokprobe debug_stack_reset(void)
 {
 	if (WARN_ON(!this_cpu_read(debug_idt_ctr)))
 		return;


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