x86/traps: Mark fixup_bad_iret() noinstr

This is called from deep entry ASM in a situation where instrumentation
will cause more harm than providing useful information.

Switch from memmove() to memcpy() because memmove() can't be called
from noinstr code. 
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505134903.346741553@linutronix.de

arch/x86/kernel/traps.c

@@ -578,7 +578,7 @@ struct bad_iret_stack {
 	struct pt_regs regs;
 };
 
-asmlinkage __visible notrace
+asmlinkage __visible noinstr
 struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 {
 	/*
@@ -589,19 +589,21 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 	 * just below the IRET frame) and we want to pretend that the
 	 * exception came from the IRET target.
 	 */
-	struct bad_iret_stack *new_stack =
-		(struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+	struct bad_iret_stack tmp, *new_stack =
+		(struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 
-	/* Copy the IRET target to the new stack. */
-	memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
+	/* Copy the IRET target to the temporary storage. */
+	memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
 
 	/* Copy the remainder of the stack from the current stack. */
-	memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
+	memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+
+	/* Update the entry stack */
+	memcpy(new_stack, &tmp, sizeof(tmp));
 
 	BUG_ON(!user_mode(&new_stack->regs));
 	return new_stack;
 }
-NOKPROBE_SYMBOL(fixup_bad_iret);
 #endif
 
 static bool is_sysenter_singlestep(struct pt_regs *regs)