1 files changed, 14 insertions, 7 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 311bcf338f07..29408d6d6626 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -105,14 +105,14 @@ ftrace_modify_code_direct(unsigned long ip, unsigned const char *old_code,
 {
 	unsigned char replaced[MCOUNT_INSN_SIZE];
 
+	ftrace_expected = old_code;
+
 	/*
-	 * Note: Due to modules and __init, code can
-	 *  disappear and change, we need to protect against faulting
-	 *  as well as code changing. We do this by using the
-	 *  probe_kernel_* functions.
-	 *
-	 * No real locking needed, this code is run through
-	 * kstop_machine, or before SMP starts.
+	 * Note:
+	 * We are paranoid about modifying text, as if a bug was to happen, it
+	 * could cause us to read or write to someplace that could cause harm.
+	 * Carefully read and modify the code with probe_kernel_*(), and make
+	 * sure what we read is what we expected it to be before modifying it.
 	 */
 
 	/* read the text we want to modify */
@@ -154,6 +154,8 @@ int ftrace_make_nop(struct module *mod,
 	if (addr == MCOUNT_ADDR)
 		return ftrace_modify_code_direct(rec->ip, old, new);
 
+	ftrace_expected = NULL;
+
 	/* Normal cases use add_brk_on_nop */
 	WARN_ONCE(1, "invalid use of ftrace_make_nop");
 	return -EINVAL;
@@ -220,6 +222,7 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 				 unsigned long addr)
 {
 	WARN_ON(1);
+	ftrace_expected = NULL;
 	return -EINVAL;
 }
 
@@ -314,6 +317,8 @@ static int add_break(unsigned long ip, const char *old)
 	if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
 		return -EFAULT;
 
+	ftrace_expected = old;
+
 	/* Make sure it is what we expect it to be */
 	if (memcmp(replaced, old, MCOUNT_INSN_SIZE) != 0)
 		return -EINVAL;
@@ -413,6 +418,8 @@ static int remove_breakpoint(struct dyn_ftrace *rec)
 		ftrace_addr = ftrace_get_addr_curr(rec);
 		nop = ftrace_call_replace(ip, ftrace_addr);
 
+		ftrace_expected = nop;
+
 		if (memcmp(&ins[1], &nop[1], MCOUNT_INSN_SIZE - 1) != 0)
 			return -EINVAL;
 	}