x86/kprobes: Use switch-case for 0xFF opcodes in prepare_emulation

For the `FF /digit` opcodes in prepare_emulation, use switch-case
instead of hand-written code to make the logic easier to understand.

Signed-off-by: Chuang Wang <nashuiliang@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20221129084022.718355-1-nashuiliang@gmail.com

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 33390ed..fd0420a 100644 (file)
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -655,17 +655,19 @@ static int prepare_emulation(struct kprobe *p, struct insn *insn)
                 * is determined by the MOD/RM byte.
                 */
                opcode = insn->modrm.bytes[0];
-               if ((opcode & 0x30) == 0x10) {
-                       if ((opcode & 0x8) == 0x8)
-                               return -EOPNOTSUPP;     /* far call */
-                       /* call absolute, indirect */
+               switch (X86_MODRM_REG(opcode)) {
+               case 0b010:     /* FF /2, call near, absolute indirect */
                        p->ainsn.emulate_op = kprobe_emulate_call_indirect;
-               } else if ((opcode & 0x30) == 0x20) {
-                       if ((opcode & 0x8) == 0x8)
-                               return -EOPNOTSUPP;     /* far jmp */
-                       /* jmp near absolute indirect */
+                       break;
+               case 0b100:     /* FF /4, jmp near, absolute indirect */
                        p->ainsn.emulate_op = kprobe_emulate_jmp_indirect;
-               } else
+                       break;
+               case 0b011:     /* FF /3, call far, absolute indirect */
+               case 0b101:     /* FF /5, jmp far, absolute indirect */
+                       return -EOPNOTSUPP;
+               }
+
+               if (!p->ainsn.emulate_op)
                        break;
 
                if (insn->addr_bytes != sizeof(unsigned long))