x86: introduce REX prefix helper for kprobes

Fold some small ifdefs into a helper function.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 19 insertions, 8 deletions

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 4e33329ce8a3..b1804e40235d 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -171,6 +171,19 @@ static void __kprobes set_jmp_op(void *from, void *to)
 }
 
 /*
+ * Check for the REX prefix which can only exist on X86_64
+ * X86_32 always returns 0
+ */
+static int __kprobes is_REX_prefix(kprobe_opcode_t *insn)
+{
+#ifdef CONFIG_X86_64
+        if ((*insn & 0xf0) == 0x40)
+                return 1;
+#endif
+        return 0;
+}
+
+/*
  * Returns non-zero if opcode is boostable.
  * RIP relative instructions are adjusted at copying time in 64 bits mode
  */
@@ -239,14 +252,14 @@ static int __kprobes is_IF_modifier(kprobe_opcode_t *insn)
         case 0x9d:              /* popf/popfd */
                 return 1;
         }
-#ifdef CONFIG_X86_64
+
         /*
-         * on 64 bit x86, 0x40-0x4f are prefixes so we need to look
+         * 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 (*insn  >= 0x40 && *insn <= 0x4f)
+        if (is_REX_prefix(insn))
                 return is_IF_modifier(++insn);
-#endif
+
         return 0;
 }
 
@@ -284,7 +297,7 @@ static void __kprobes fix_riprel(struct kprobe *p)
         }
 
         /* Skip REX instruction prefix.  */
-        if ((*insn & 0xf0) == 0x40)
+        if (is_REX_prefix(insn))
                 ++insn;
 
         if (*insn == 0x0f) {
@@ -748,11 +761,9 @@ static void __kprobes resume_execution(struct kprobe *p,
         unsigned long orig_ip = (unsigned long)p->addr;
         kprobe_opcode_t *insn = p->ainsn.insn;
 
-#ifdef CONFIG_X86_64
         /*skip the REX prefix*/
-        if (*insn >= 0x40 && *insn <= 0x4f)
+        if (is_REX_prefix(insn))
                 insn++;
-#endif
 
         regs->flags &= ~X86_EFLAGS_TF;
         switch (*insn) {