lkdtm: flush icache and report actions

Some CPUs explicitly need to have their icache flushed after making
executable code copies for the memory region execution tests.
Additionally, report the specific address targets being used so that
debugging non-crash failures is easier.

Signed-off-by: Kees Cook <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/lkdtm.c

···
 {
 	void (*func)(void) = dst;
 
+	pr_info("attempting ok execution at %p\n", do_nothing);
+	do_nothing();
+
 	memcpy(dst, do_nothing, EXEC_SIZE);
+	flush_icache_range((unsigned long)dst, (unsigned long)dst + EXEC_SIZE);
+	pr_info("attempting bad execution at %p\n", func);
 	func();
 }
 
···
 	/* Intentionally crossing kernel/user memory boundary. */
 	void (*func)(void) = dst;
 
+	pr_info("attempting ok execution at %p\n", do_nothing);
+	do_nothing();
+
 	if (copy_to_user((void __user *)dst, do_nothing, EXEC_SIZE))
 		return;
+	flush_icache_range((unsigned long)dst, (unsigned long)dst + EXEC_SIZE);
+	pr_info("attempting bad execution at %p\n", func);
 	func();
 }
 
···
 		}
 
 		ptr = (unsigned long *)user_addr;
+
+		pr_info("attempting bad read at %p\n", ptr);
 		tmp = *ptr;
 		tmp += 0xc0dec0de;
+
+		pr_info("attempting bad write at %p\n", ptr);
 		*ptr = tmp;
 
 		vm_munmap(user_addr, PAGE_SIZE);
···
 		unsigned long *ptr;
 
 		ptr = (unsigned long *)&rodata;
+
+		pr_info("attempting bad write at %p\n", ptr);
 		*ptr ^= 0xabcd1234;
 
 		break;