linux-kernel - Re: [PATCH 2/2] kernel: add support for live patching

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Message-ID: <545D2036.9080205@amacapital.net>
Date:	Fri, 07 Nov 2014 11:40:38 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Seth Jennings <sjenning@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	live-patching@...r.kernel.org, kpatch@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kernel: add support for live patching

On 11/06/2014 06:39 AM, Seth Jennings wrote:
> This commit introduces code for the live patching core.  It implements
> an ftrace-based mechanism and kernel interface for doing live patching
> of kernel and kernel module functions.
> 
> It represents the greatest common functionality set between kpatch and
> kgraft and can accept patches built using either method.
> 
> This first version does not implement any consistency mechanism that
> ensures that old and new code do not run together.  In practice, ~90% of
> CVEs are safe to apply in this way, since they simply add a conditional
> check.  However, any function change that can not execute safely with
> the old version of the function can _not_ be safely applied in this
> version.
> 

[...]

> +/********************************************
> + * Sysfs Interface
> + *******************************************/
> +/*
> + * /sys/kernel/livepatch
> + * /sys/kernel/livepatch/<patch>
> + * /sys/kernel/livepatch/<patch>/enabled
> + * /sys/kernel/livepatch/<patch>/<object>
> + * /sys/kernel/livepatch/<patch>/<object>/<func>
> + * /sys/kernel/livepatch/<patch>/<object>/<func>/new_addr
> + * /sys/kernel/livepatch/<patch>/<object>/<func>/old_addr
> + */

Letting anyone read new_addr and old_addr is a kASLR leak, and I would
argue that showing this information to non-root at all is probably a bad
idea.

Can you make new_addr and old_addr have mode 0600 and
/sys/kernel/livepatch itself have mode 0500?  For the latter, an admin
who wants unprivileged users to be able to see it can easily chmod it.

--Andy
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