linux-kernel - Re: [GIT PULL] x86/kaslr for v3.14

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Message-ID: <CAGXu5jLdz2b2gozgK_TWjUzGacwyD_qb47Yc8rkmWkzVe1zcWg@mail.gmail.com>
Date:	Tue, 21 Jan 2014 10:37:00 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Cong Ding <dinggnu@...il.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mathias Krause <minipli@...glemail.com>,
	Michael Davidson <md@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
Subject: Re: [GIT PULL] x86/kaslr for v3.14

On Tue, Jan 21, 2014 at 6:20 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 01/21/2014 01:00 AM, Peter Zijlstra wrote:
>>>
>>> So this is presumably something that needs to be fixed in perf?
>>
>> Where do we learn about the offset from userspace?
>
> Now this is tricky... if this offset is too easy to get it completely
> defeats kASLR.  On the other hand, I presume that if we are exporting
> /proc/kcore we're not secure anyway.  Kees, I assume that in "secure"
> mode perf annotations simply wouldn't work anyway?

The goal scope of the kernel base address randomization is to keep it
secret from non-root users, confined processes, and/or remote systems.
For local secrecy, if you're running with kaslr and you haven't set
kptr_restrict, dmesg_restrict, and perf_event_paranoid, that's a
problem since you're likely leaking things trivially through
/proc/kallsyms, dmesg, and/or perf.

-Kees

-- 
Kees Cook
Chrome OS Security
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