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

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Message-ID: <CAGXu5jKp0j71ucE7uOWRa+gQM1Wzp=_KdByJK4XnACTwiCW4ow@mail.gmail.com>
Date:	Fri, 31 Jan 2014 08:57:03 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	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>,
	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 Thu, Jan 30, 2014 at 2:07 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Sun, Jan 26, 2014 at 10:51:06PM -0800, H. Peter Anvin 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...
>
> I am wondering if kdump functionality is impacted with this change.
>
> Kexec tools prepares ELF headers for kernel memory ranges and for the
> range where kernel text is mapped. So it needs to know virtual address
> of the region where kernel is mapped (obtained by /proc/kcore) and
> it gets the physical address where kernel is loaded from /proc/iomem.
>
> So with this change are we planning to hide kernel text virtual address and
> physical address information information from root in /proc/kcore and
> /proc/iomem in anyway?

I have no intention of that. Mentioned earlier in the thread, hiding
it from root will be pretty ugly/hard/pointless:
https://lkml.org/lkml/2014/1/27/287
I would like to just keep the offset out of dmesg.

-Kees

-- 
Kees Cook
Chrome OS Security
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