Message-ID: <515F340F.4060202@zytor.com>
Date: Fri, 05 Apr 2013 13:29:03 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4
MIME-Version: 1.0
To: Yinghai Lu <yinghai@kernel.org>
CC: Kees Cook <keescook@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        kernel-hardening@lists.openwall.com,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@intel.com>,
        Matthew Garrett <mjg@redhat.com>,
        Matt Fleming <matt.fleming@intel.com>,
        Eric Northup <digitaleric@google.com>,
        Dan Rosenberg <drosenberg@vsecurity.com>,
        Julien Tinnes <jln@google.com>, Will Drewry <wad@chromium.org>
Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR
References: <1365106055-22939-1-git-send-email-keescook@chromium.org> <1365106055-22939-4-git-send-email-keescook@chromium.org> <515DE0C9.3030709@zytor.com> <CAE9FiQVCC2-yF0+bt2MryHDs2vK8bcsU1aE-is_ejDDF0dTbMQ@mail.gmail.com> <515F2E81.9000900@zytor.com> <CAE9FiQU+k0j-CEvJm-D6Dch4wa8ooU8Zcry8sN0RYx=YEadiJw@mail.gmail.com>
In-Reply-To: <CAE9FiQU+k0j-CEvJm-D6Dch4wa8ooU8Zcry8sN0RYx=YEadiJw@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1337
Lines: 36

On 04/05/2013 01:19 PM, Yinghai Lu wrote:
> On Fri, Apr 5, 2013 at 1:05 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> 
>> That makes zero difference, since the issue at hand is the *virtual*
>> addresses the kernel are running at.  Currently, the 64-bit kernel
>> always runs at 0xffffffff81000000 virtual.  We can't run out of
>> arbitrary bits of the 64-bit address space because of the memory model.
> 
> Not sure if I understand this.
> 
> when bzImage64 is loaded high,  the kernel high address 0xffffffff81000000
> is pointed to phys address above 4G without problem.
> 

That' s the problem.

KASLR is about randomizing the *virtual* address space, not the
*physical* address space.  On 32 bits those are connected (which is a
problem all on its own), on 64 bits not so much.

>>
>> Furthermore, dealing with the boot loaders means dealing with the boot
>> loader maintainers, which can be insanely painful.  Consider that Grub2,
>> 10 years after this was implemented, still can't load more than one
>> initramfs component.
> 
> syslinux and pxelinux could do that?
> 

Yes, they can.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/