linux-kernel - Re: [PATCH 3/7] uretprobes/x86: hijack return address

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Message-ID: <20130324145942.GB17037@redhat.com>
Date:	Sun, 24 Mar 2013 15:59:42 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	adrian.m.negreanu@...el.com, Torsten.Polle@....de
Subject: Re: [PATCH 3/7] uretprobes/x86: hijack return address

On 03/22, Anton Arapov wrote:
>
> +arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs)
> +{
> +	int rasize, ncopied;
> +	unsigned long orig_ret_vaddr = 0; /* clear high bits for 32-bit apps */
> +
> +	rasize = is_ia32_task() ? 4 : 8;

Hmm.. I guess you need is_compat_task() here.

> +	ncopied = copy_from_user(&orig_ret_vaddr, (void __user *)regs->sp, rasize);
> +	if (unlikely(ncopied))
> +		return -1;
> +
> +	/* check whether address has been already hijacked */
> +	if (orig_ret_vaddr == trampoline_vaddr)
> +		return orig_ret_vaddr;
> +
> +	ncopied = copy_to_user((void __user *)regs->sp, &trampoline_vaddr, rasize);
> +	if (unlikely(ncopied)) {
> +		if (ncopied != rasize) {
> +			printk(KERN_ERR "uprobe: return address clobbered: "

Cosmetic, but we have pr_err().

> +					"pid=%d, %%sp=%#lx, %%ip=%#lx\n",
> +					current->pid, regs->sp, regs->ip);
> +			/* kill task immediately */
> +			send_sig(SIGSEGV, current, 0);

probably force_sig_info() makes more sense, but this is minor

> +		}

You need to retun -1 here.

Cosmetic again, but since this function should be updated anyway,
I'd suggest

	ncopied = copy_to_user(...);

	if (likely(!ncopied))
		return orig_ret_vaddr;

	if (ncopied != rasize) {
		...
	}

	return -1;

Oleg.

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