4 files changed, 40 insertions, 8 deletions

diff --git a/arch/x86/include/asm/debugreg.h b/arch/x86/include/asm/debugreg.h
index 078ad0caefc..b903d5ea394 100644
--- a/arch/x86/include/asm/debugreg.h
+++ b/arch/x86/include/asm/debugreg.h
@@ -101,6 +101,28 @@ extern void aout_dump_debugregs(struct user *dump);
 
 extern void hw_breakpoint_restore(void);
 
+#ifdef CONFIG_X86_64
+DECLARE_PER_CPU(int, debug_stack_usage);
+static inline void debug_stack_usage_inc(void)
+{
+        __get_cpu_var(debug_stack_usage)++;
+}
+static inline void debug_stack_usage_dec(void)
+{
+        __get_cpu_var(debug_stack_usage)--;
+}
+int is_debug_stack(unsigned long addr);
+void debug_stack_set_zero(void);
+void debug_stack_reset(void);
+#else /* !X86_64 */
+static inline int is_debug_stack(unsigned long addr) { return 0; }
+static inline void debug_stack_set_zero(void) { }
+static inline void debug_stack_reset(void) { }
+static inline void debug_stack_usage_inc(void) { }
+static inline void debug_stack_usage_dec(void) { }
+#endif /* X86_64 */
+
+
 #endif  /* __KERNEL__ */
 
 #endif /* _ASM_X86_DEBUGREG_H */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 4b39d6d7e3a..b650435ffb5 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -402,9 +402,6 @@ DECLARE_PER_CPU(char *, irq_stack_ptr);
 DECLARE_PER_CPU(unsigned int, irq_count);
 extern unsigned long kernel_eflags;
 extern asmlinkage void ignore_sysret(void);
-int is_debug_stack(unsigned long addr);
-void debug_stack_set_zero(void);
-void debug_stack_reset(void);
 #else   /* X86_64 */
 #ifdef CONFIG_CC_STACKPROTECTOR
 /*
@@ -419,9 +416,6 @@ struct stack_canary {
 };
 DECLARE_PER_CPU_ALIGNED(struct stack_canary, stack_canary);
 #endif
-static inline int is_debug_stack(unsigned long addr) { return 0; }
-static inline void debug_stack_set_zero(void) { }
-static inline void debug_stack_reset(void) { }
 #endif  /* X86_64 */
 
 extern unsigned int xstate_size;
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index caa404556b9..266e4649b1d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1093,11 +1093,13 @@ unsigned long kernel_eflags;
 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)
 {
-        return addr <= __get_cpu_var(debug_stack_addr) &&
-                addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ);
+        return __get_cpu_var(debug_stack_usage) ||
+                (addr <= __get_cpu_var(debug_stack_addr) &&
+                 addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ));
 }
 
 void debug_stack_set_zero(void)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a93c5cabc36..0072b38e3ea 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -316,9 +316,15 @@ dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
                 return;
 #endif
 
+        /*
+         * Let others (NMI) know that the debug stack is in use
+         * as we may switch to the interrupt stack.
+         */
+        debug_stack_usage_inc();
         preempt_conditional_sti(regs);
         do_trap(3, SIGTRAP, "int3", regs, error_code, NULL);
         preempt_conditional_cli(regs);
+        debug_stack_usage_dec();
 }
 
 #ifdef CONFIG_X86_64
@@ -411,6 +417,12 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
                                                         SIGTRAP) == NOTIFY_STOP)
                 return;
 
+        /*
+         * Let others (NMI) know that the debug stack is in use
+         * as we may switch to the interrupt stack.
+         */
+        debug_stack_usage_inc();
+
         /* It's safe to allow irq's after DR6 has been saved */
         preempt_conditional_sti(regs);
 
@@ -418,6 +430,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
                 handle_vm86_trap((struct kernel_vm86_regs *) regs,
                                 error_code, 1);
                 preempt_conditional_cli(regs);
+                debug_stack_usage_dec();
                 return;
         }
 
@@ -437,6 +450,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
         if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
                 send_sigtrap(tsk, regs, error_code, si_code);
         preempt_conditional_cli(regs);
+        debug_stack_usage_dec();
 
         return;
 }