[patch V4 part 4 14/24] x86/nmi: Protect NMI entry against instrumentation

[Thomas Gleixner <tglx@linutronix.de>]

Mark all functions in the fragile code parts noinstr or force inlining so
they can't be instrumented.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/desc.h  |    8 ++++----
 arch/x86/kernel/cpu/common.c |    6 ++----
 arch/x86/kernel/nmi.c        |   10 ++++++----
 3 files changed, 12 insertions(+), 12 deletions(-)

--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -214,7 +214,7 @@ static inline void native_load_gdt(const
 	asm volatile("lgdt %0"::"m" (*dtr));
 }
 
-static inline void native_load_idt(const struct desc_ptr *dtr)
+static __always_inline void native_load_idt(const struct desc_ptr *dtr)
 {
 	asm volatile("lidt %0"::"m" (*dtr));
 }
@@ -393,7 +393,7 @@ extern unsigned long system_vectors[];
 
 #ifdef CONFIG_X86_64
 DECLARE_PER_CPU(u32, debug_idt_ctr);
-static inline bool is_debug_idt_enabled(void)
+static __always_inline bool is_debug_idt_enabled(void)
 {
 	if (this_cpu_read(debug_idt_ctr))
 		return true;
@@ -401,7 +401,7 @@ static inline bool is_debug_idt_enabled(
 	return false;
 }
 
-static inline void load_debug_idt(void)
+static __always_inline void load_debug_idt(void)
 {
 	load_idt((const struct desc_ptr *)&debug_idt_descr);
 }
@@ -423,7 +423,7 @@ static inline void load_debug_idt(void)
  * that doesn't need to disable interrupts, as nothing should be
  * bothering the CPU then.
  */
-static inline void load_current_idt(void)
+static __always_inline void load_current_idt(void)
 {
 	if (is_debug_idt_enabled())
 		load_debug_idt();
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1692,21 +1692,19 @@ void syscall_init(void)
 DEFINE_PER_CPU(int, debug_stack_usage);
 DEFINE_PER_CPU(u32, debug_idt_ctr);
 
-void debug_stack_set_zero(void)
+noinstr void debug_stack_set_zero(void)
 {
 	this_cpu_inc(debug_idt_ctr);
 	load_current_idt();
 }
-NOKPROBE_SYMBOL(debug_stack_set_zero);
 
-void debug_stack_reset(void)
+noinstr void debug_stack_reset(void)
 {
 	if (WARN_ON(!this_cpu_read(debug_idt_ctr)))
 		return;
 	if (this_cpu_dec_return(debug_idt_ctr) == 0)
 		load_current_idt();
 }
-NOKPROBE_SYMBOL(debug_stack_reset);
 
 #else	/* CONFIG_X86_64 */
 
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -307,7 +307,7 @@ NOKPROBE_SYMBOL(unknown_nmi_error);
 static DEFINE_PER_CPU(bool, swallow_nmi);
 static DEFINE_PER_CPU(unsigned long, last_nmi_rip);
 
-static void default_do_nmi(struct pt_regs *regs)
+static noinstr void default_do_nmi(struct pt_regs *regs)
 {
 	unsigned char reason = 0;
 	int handled;
@@ -333,6 +333,7 @@ static void default_do_nmi(struct pt_reg
 
 	__this_cpu_write(last_nmi_rip, regs->ip);
 
+	instr_begin();
 	handled = nmi_handle(NMI_LOCAL, regs);
 	__this_cpu_add(nmi_stats.normal, handled);
 	if (handled) {
@@ -346,6 +347,7 @@ static void default_do_nmi(struct pt_reg
 		 */
 		if (handled > 1)
 			__this_cpu_write(swallow_nmi, true);
+		instr_end();
 		return;
 	}
 
@@ -378,6 +380,7 @@ static void default_do_nmi(struct pt_reg
 #endif
 		__this_cpu_add(nmi_stats.external, 1);
 		raw_spin_unlock(&nmi_reason_lock);
+		instr_end();
 		return;
 	}
 	raw_spin_unlock(&nmi_reason_lock);
@@ -416,8 +419,8 @@ static void default_do_nmi(struct pt_reg
 		__this_cpu_add(nmi_stats.swallow, 1);
 	else
 		unknown_nmi_error(reason, regs);
+	instr_end();
 }
-NOKPROBE_SYMBOL(default_do_nmi);
 
 /*
  * NMIs can page fault or hit breakpoints which will cause it to lose
@@ -489,7 +492,7 @@ static DEFINE_PER_CPU(unsigned long, nmi
  */
 static DEFINE_PER_CPU(int, update_debug_stack);
 
-static bool notrace is_debug_stack(unsigned long addr)
+static noinstr bool is_debug_stack(unsigned long addr)
 {
 	struct cea_exception_stacks *cs = __this_cpu_read(cea_exception_stacks);
 	unsigned long top = CEA_ESTACK_TOP(cs, DB);
@@ -504,7 +507,6 @@ static bool notrace is_debug_stack(unsig
 	 */
 	return addr >= bot && addr < top;
 }
-NOKPROBE_SYMBOL(is_debug_stack);
 #endif
 
 DEFINE_IDTENTRY_NMI(exc_nmi)