ftrace: return error on failed modified text.

Have the ftrace_modify_code return error values:

  -EFAULT on error of reading the address

  -EINVAL if what is read does not match what it expected

  -EPERM  if the write fails to update after a successful match.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/ftrace.c

@@ -62,7 +62,6 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
 		   unsigned char *new_code)
 {
 	unsigned char replaced[MCOUNT_INSN_SIZE];
-	int ret;
 
 	/*
 	 * Note: Due to modules and __init, code can
@@ -72,15 +71,16 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
 	 * No real locking needed, this code is run through
 	 * kstop_machine, or before SMP starts.
 	 */
-	if (__copy_from_user_inatomic(replaced, (char __user *)ip, MCOUNT_INSN_SIZE))
-		return 1;
+	if (__copy_from_user_inatomic(replaced, (char __user *)ip,
+				      MCOUNT_INSN_SIZE))
+		return -EFAULT;
 
 	if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
-		return 2;
+		return -EINVAL;
 
-	ret = __copy_to_user_inatomic((char __user *)ip, new_code,
-					MCOUNT_INSN_SIZE);
-	WARN_ON_ONCE(ret);
+	if (__copy_to_user_inatomic((char __user *)ip, new_code,
+				    MCOUNT_INSN_SIZE))
+		return -EPERM;
 
 	sync_core();
 

include/linux/ftrace.h

@@ -72,13 +72,33 @@ extern unsigned char *ftrace_nop_replace(void);
 extern unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr);
 extern int ftrace_dyn_arch_init(void *data);
 extern int ftrace_mcount_set(unsigned long *data);
-extern int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
-			      unsigned char *new_code);
 extern int ftrace_update_ftrace_func(ftrace_func_t func);
 extern void ftrace_caller(void);
 extern void ftrace_call(void);
 extern void mcount_call(void);
 
+/**
+ * ftrace_modify_code - modify code segment
+ * @ip: the address of the code segment
+ * @old_code: the contents of what is expected to be there
+ * @new_code: the code to patch in
+ *
+ * This is a very sensitive operation and great care needs
+ * to be taken by the arch.  The operation should carefully
+ * read the location, check to see if what is read is indeed
+ * what we expect it to be, and then on success of the compare,
+ * it should write to the location.
+ *
+ * Return must be:
+ *  0 on success
+ *  -EFAULT on error reading the location
+ *  -EINVAL on a failed compare of the contents
+ *  -EPERM  on error writing to the location
+ * Any other value will be considered a failure.
+ */
+extern int ftrace_modify_code(unsigned long ip, unsigned char *old_code,
+			      unsigned char *new_code);
+
 extern int skip_trace(unsigned long ip);
 
 extern void ftrace_release(void *start, unsigned long size);

kernel/trace/ftrace.c

@@ -596,22 +596,22 @@ ftrace_code_disable(struct dyn_ftrace *rec)
 {
 	unsigned long ip;
 	unsigned char *nop, *call;
-	int failed;
+	int ret;
 
 	ip = rec->ip;
 
 	nop = ftrace_nop_replace();
 	call = ftrace_call_replace(ip, mcount_addr);
 
-	failed = ftrace_modify_code(ip, call, nop);
-	if (failed) {
-		switch (failed) {
-		case 1:
+	ret = ftrace_modify_code(ip, call, nop);
+	if (ret) {
+		switch (ret) {
+		case -EFAULT:
 			WARN_ON_ONCE(1);
 			pr_info("ftrace faulted on modifying ");
 			print_ip_sym(ip);
 			break;
-		case 2:
+		case -EINVAL:
 			WARN_ON_ONCE(1);
 			pr_info("ftrace failed to modify ");
 			print_ip_sym(ip);
@@ -620,6 +620,15 @@ ftrace_code_disable(struct dyn_ftrace *rec)
 			print_ip_ins(" replace: ", nop);
 			printk(KERN_CONT "\n");
 			break;
+		case -EPERM:
+			WARN_ON_ONCE(1);
+			pr_info("ftrace faulted on writing ");
+			print_ip_sym(ip);
+			break;
+		default:
+			WARN_ON_ONCE(1);
+			pr_info("ftrace faulted on unknown error ");
+			print_ip_sym(ip);
 		}
 
 		rec->flags |= FTRACE_FL_FAILED;