Subject: Re: [PATCH][v2] uprobes/x86: emulate push insns for uprobe on x86

From: Oleg Nesterov <[email-masked]>
Date: Mon, 13 Nov 2017 13:59:56 +0100

The patch looks good to me, but I have a question because I know nothing
about insn encoding,

On 11/10, Yonghong Song wrote:
>
> +static int push_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
> +{
> +	u8 opc1 = OPCODE1(insn), reg_offset = 0;
> +
> +	if (opc1 < 0x50 || opc1 > 0x57)
> +		return -ENOSYS;
> +
> +	if (insn->length > 2)
> +		return -ENOSYS;
> +	if (insn->length == 2) {
> +		/* only support rex_prefix 0x41 (x64 only) */
> +#ifdef CONFIG_X86_64
> +		if (insn->rex_prefix.nbytes != 1 ||
> +		    insn->rex_prefix.bytes[0] != 0x41)
> +			return -ENOSYS;
> +
> +		auprobe->push.ilen = 2;

and the "else" branch does

		auprobe->push.ilen = 1;

you could add
		auprobe->push.ilen = insn->length;

at the end of push_setup_xol_ops() instead, but this is minor/cosmetic,

> +		switch (opc1) {
> +		case 0x50:
> +			reg_offset = offsetof(struct pt_regs, r8);
> +			break;
> +		case 0x51:
> +			reg_offset = offsetof(struct pt_regs, r9);
> +			break;
> +		case 0x52:
> +			reg_offset = offsetof(struct pt_regs, r10);
> +			break;
> +		case 0x53:
> +			reg_offset = offsetof(struct pt_regs, r11);
> +			break;
> +		case 0x54:
> +			reg_offset = offsetof(struct pt_regs, r12);
> +			break;
> +		case 0x55:
> +			reg_offset = offsetof(struct pt_regs, r13);
> +			break;
> +		case 0x56:
> +			reg_offset = offsetof(struct pt_regs, r14);
> +			break;
> +		case 0x57:
> +			reg_offset = offsetof(struct pt_regs, r15);
> +			break;
> +		}
> +#else
> +		return -ENOSYS;
> +#endif

OK, but shouldn't we also return ENOSYS if CONFIG_X86_64=y but the probed task is 32bit?

Or in this case uprobe_init_insn(x86_64 => false) should fail and push_setup_xol_ops()
won't be called?

Oleg.