linux-kernel - Re: [PATCH] uprobes/x86: emulate push insns for uprobe on x86

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Message-ID: <20171109144738.GA12923@redhat.com>
Date:   Thu, 9 Nov 2017 15:47:38 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Yonghong Song <yhs@...com>
Cc:     mingo@...nel.org, tglx@...utronix.de, peterz@...radead.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        netdev@...r.kernel.org, ast@...com, kernel-team@...com
Subject: Re: [PATCH] uprobes/x86: emulate push insns for uprobe on x86

On 11/09, Yonghong Song wrote:
>
> +	if (insn_class == UPROBE_PUSH_INSN) {
> +		src_ptr = get_push_reg_ptr(auprobe, regs);
> +		reg_width = sizeof_long();
> +		sp = regs->sp;
> +		if (copy_to_user((void __user *)(sp - reg_width), src_ptr, reg_width))
> +			return false;
> +
> +		regs->sp = sp - reg_width;
> +		regs->ip += 1 + (auprobe->push.rex_prefix != 0);
> +		return true;

Another nit... You can rename push_ret_address() and use it here

		src_ptr = ...;
		if (push_ret_address(regs, *src_ptr))
			return false;

		regs->ip += ...;
		return true;

and I think get_push_reg_ptr() should just return "unsigned long", not the
pointer.

And again, please make a separate method for this code. Let me repeat, the
main reason for branch_xol_ops/etc is that we simply can not execute these
insns out-of-line, we have to emulate them. "push" differs, the only reason
why we may want to emulate it is optimization.

Oleg.