linux-kernel - Re: [PATCH 7/7] uprobes/x86: Introduce uprobe_xol_ops and arch

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Date:	Thu, 3 Apr 2014 21:49:27 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jonathan Lebon <jlebon@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] uprobes/x86: Introduce uprobe_xol_ops and
	arch_uprobe->ops

On 04/02, Jim Keniston wrote:
>
> On Mon, 2014-03-31 at 21:44 +0200, Oleg Nesterov wrote:
> ...
> > +/*
> > + * Adjust the return address pushed by a call insn executed out of line.
> > + */
> > +static int adjust_ret_addr(unsigned long sp, long correction)
> > +{
> > +	int rasize, ncopied;
> > +	long ra = 0;
> > +
> > +	if (is_ia32_task())
> > +		rasize = 4;
> > +	else
> > +		rasize = 8;
> > +
> > +	ncopied = copy_from_user(&ra, (void __user *)sp, rasize);
> > +	if (unlikely(ncopied))
> > +		return -EFAULT;
> > +
> > +	ra += correction;
> > +	ncopied = copy_to_user((void __user *)sp, &ra, rasize);
> > +	if (unlikely(ncopied))
> > +		return -EFAULT;
> > +
> > +	return 0;
> > +}
>
> This isn't your bug, Oleg -- you're just moving code -- but consider
> taking this opportunity to fix it...
>
> "ncopied" is a misnomer here.  copy_from_user() and copy_to_user()
> return the number of bytes that could NOT be copied.

Yes, thanks. I'll try to cleanup this later. I am not sure yet, but
perhaps I will change adjust_ret_addr() and hijack_return_addr() to
use a couple of new get/put_user helpers, because ->call_emulate()
needs to check is_ia32_task() and write to *sp too.

Thanks.

Oleg.

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