---

yaml
---
r: 205295
b: refs/heads/master
c: 567a9fd
h: refs/heads/master
i:
  205293: 9782d8f
  205291: da4373a
  205287: 06d0035
  205279: 90c2a02
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: a1d0ce8213e9ddf4046ef5ba95c55762d075f541
+refs/heads/master: 567a9fd86735ccdc897768ed2dacdd5e83a13509

trunk/arch/x86/kernel/kprobes.c

@@ -126,16 +126,22 @@ static void __kprobes synthesize_reljump(void *from, void *to)
 }
 
 /*
- * Check for the REX prefix which can only exist on X86_64
- * X86_32 always returns 0
+ * Skip the prefixes of the instruction.
  */
-static int __kprobes is_REX_prefix(kprobe_opcode_t *insn)
+static kprobe_opcode_t *__kprobes skip_prefixes(kprobe_opcode_t *insn)
 {
+	insn_attr_t attr;
+
+	attr = inat_get_opcode_attribute((insn_byte_t)*insn);
+	while (inat_is_legacy_prefix(attr)) {
+		insn++;
+		attr = inat_get_opcode_attribute((insn_byte_t)*insn);
+	}
 #ifdef CONFIG_X86_64
-	if ((*insn & 0xf0) == 0x40)
-		return 1;
+	if (inat_is_rex_prefix(attr))
+		insn++;
 #endif
-	return 0;
+	return insn;
 }
 
 /*
@@ -272,6 +278,9 @@ static int __kprobes can_probe(unsigned long paddr)
  */
 static int __kprobes is_IF_modifier(kprobe_opcode_t *insn)
 {
+	/* Skip prefixes */
+	insn = skip_prefixes(insn);
+
 	switch (*insn) {
 	case 0xfa:		/* cli */
 	case 0xfb:		/* sti */
@@ -280,13 +289,6 @@ static int __kprobes is_IF_modifier(kprobe_opcode_t *insn)
 		return 1;
 	}
 
-	/*
-	 * on X86_64, 0x40-0x4f are REX prefixes so we need to look
-	 * at the next byte instead.. but of course not recurse infinitely
-	 */
-	if (is_REX_prefix(insn))
-		return is_IF_modifier(++insn);
-
 	return 0;
 }
 
@@ -803,9 +805,8 @@ static void __kprobes resume_execution(struct kprobe *p,
 	unsigned long orig_ip = (unsigned long)p->addr;
 	kprobe_opcode_t *insn = p->ainsn.insn;
 
-	/*skip the REX prefix*/
-	if (is_REX_prefix(insn))
-		insn++;
+	/* Skip prefixes */
+	insn = skip_prefixes(insn);
 
 	regs->flags &= ~X86_EFLAGS_TF;
 	switch (*insn) {