Re: [PATCH] x86/kprobes: Use switch-case for 0xFF opcodes in prepare_emulation

From: Google
Date: Wed Nov 30 2022 - 08:38:41 EST


On Tue, 29 Nov 2022 16:39:51 +0800
Chuang Wang <nashuiliang@xxxxxxxxx> wrote:

> 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@xxxxxxxxx>

This looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Thank you!

> ---
> arch/x86/kernel/kprobes/core.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 66299682b6b7..66ec32b6cd0e 100644
> --- 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))
> --
> 2.37.2
>


--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>