linux-kernel - Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch methods (v6)

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Message-ID: <20131104155131.GD4440@redhat.com>
Date:	Mon, 4 Nov 2013 16:51:31 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCHSET 00/13] tracing/uprobes: Add support for more fetch
	methods (v6)

On 11/04, Namhyung Kim wrote:
> On Mon, 04 Nov 2013 17:46:41 +0900, Namhyung Kim wrote:
> > On Sat, 2 Nov 2013 16:54:58 +0100, Oleg Nesterov wrote:
> >> - this only allows to read the data from the same binary.
> >
> > Right.  This is also an unnecessary restriction.  We should be able to
> > access data in other binary.
>
> Hmm.. I guess this gonna be not simple

Yes ;)

- perhaps it can only be
> supported for per-process uprobe with known virtual addresses?

"Known" is very limited. Even in the simplest case (like your test-case
from from 0/13), you simply can't know the address of "int glob" if you
compile it with "-pie -fPIC".

As for other binaries (say libc) the problem is even worse, and
randomize_va_space adds even more pain.

But in any case, I strongly believe that it doesn't make any sense to
rely on tu->inode in get_user_vaddr().

Oleg.

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