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

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Date:	Mon, 27 Jan 2014 08:43:35 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Richard Weinberger <richard.weinberger@...il.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Cong Ding <dinggnu@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Kees Cook <keescook@...omium.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


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * H. Peter Anvin <hpa@...or.com> wrote:
> 
> > On 01/26/2014 10:49 PM, Richard Weinberger wrote:
> > >>
> > >> No, because that information is available to user space unless we panic.
> > > 
> > > Didn't you mean non-root?
> > > I thought one has to set dmesg_restrict anyways if kASLR is used.
> > > 
> > > And isn't the offset available to perf too?
> > > Of course only for root, but still user space.
> > > 
> > 
> > For certain system security levels one want to protect even from a 
> > rogue root.  In those cases, leaking that information via dmesg and 
> > perf isn't going to work, either.
> > 
> > With lower security settings, by all means...
> 
> The 'no' was categorical and unconditional though, so is the right 
> answer perhaps something more along the lines of:
> 
>   'Yes, the random offset can be reported in an oops, as long as
>    high security setups can turn off the reporting of the offset,
>    in their idealistic attempt to protect the system against root.'
> 
> ?

'reporting of the offset' should probably be 'reporting kernel data' - 
there's many possible ways an oops (and its associated raw stack dump) 
can leak the offset, I'm not sure this can ever be made 'safe' against 
a rougue root.

Not giving kernel originated debug information at all would. (At the 
cost of reducing the utility of having that root user around, of 
course.)

Thanks,

	Ingo
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