Subject: Re: [PATCH][v3] uprobes/x86: emulate push insns for uprobe on x86

From: Oleg Nesterov <[email-masked]>
Date: Tue, 14 Nov 2017 16:51:24 +0100

On 11/13, 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;
> +#ifdef CONFIG_X86_64
> +	if (test_thread_flag(TIF_ADDR32))
> +		return -ENOSYS;
> +#endif

No, this doesn't look right, see my previous email. You should do this
check in the "if (insn->length == 2)" branch below, "push bp" should be
emulated correctly.

And test_thread_flag(TIF_ADDR32) is not right too. The caller is not
necessarily the probed task. See is_64bit_mm(mm) in arch_uprobe_analyze_insn().

And again... please check if uprobe_init_insn() fails or not in this case
(32bit task does, say, "push r8"). If it fails, your V2 should be fine.

To remind, uprobes && 32-bit is broken, let me quote my another email:

	The 3rd bug means that you simply can't uprobe a 32bit task on a 64bit
	system, the in_compat_syscall() logic in get_unmapped_area() looks very
	wrong although I need to re-check.

I didn't have time for this problem so far. But emulation should work, so
you can hopefully test your patch.

Oleg.