1 files changed, 13 insertions, 25 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 4151c91254e8..082d99642622 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -11,6 +11,7 @@
 
 #include <linux/spinlock.h>
 #include <linux/hardirq.h>
+#include <linux/uaccess.h>
 #include <linux/ftrace.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
@@ -60,11 +61,7 @@ notrace int
 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
                    unsigned char *new_code)
 {
-        unsigned replaced;
-        unsigned old = *(unsigned *)old_code; /* 4 bytes */
-        unsigned new = *(unsigned *)new_code; /* 4 bytes */
-        unsigned char newch = new_code[4];
-        int faulted = 0;
+        unsigned char replaced[MCOUNT_INSN_SIZE];
 
         /*
          * Note: Due to modules and __init, code can
@@ -72,29 +69,20 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
          *  as well as code changing.
          *
          * No real locking needed, this code is run through
-         * kstop_machine.
+         * kstop_machine, or before SMP starts.
          */
-        asm volatile (
-                "1: lock\n"
-                "   cmpxchg %3, (%2)\n"
-                "   jnz 2f\n"
-                "   movb %b4, 4(%2)\n"
-                "2:\n"
-                ".section .fixup, \"ax\"\n"
-                "3:     movl $1, %0\n"
-                "       jmp 2b\n"
-                ".previous\n"
-                _ASM_EXTABLE(1b, 3b)
-                : "=r"(faulted), "=a"(replaced)
-                : "r"(ip), "r"(new), "c"(newch),
-                  "0"(faulted), "a"(old)
-                : "memory");
-        sync_core();
+        if (__copy_from_user(replaced, (char __user *)ip, MCOUNT_INSN_SIZE))
+                return 1;
 
-        if (replaced != old && replaced != new)
-                faulted = 2;
+        if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
+                return 2;
 
-        return faulted;
+        WARN_ON_ONCE(__copy_to_user((char __user *)ip, new_code,
+                                    MCOUNT_INSN_SIZE));
+
+        sync_core();
+
+        return 0;
 }
 
 notrace int ftrace_update_ftrace_func(ftrace_func_t func)