User-Agent: K-9 Mail for Android
In-Reply-To: <5718D5F0.8010501@oracle.com>
References: <1460757793-59020-1-git-send-email-thgarnie@google.com> <1460757793-59020-4-git-send-email-thgarnie@google.com> <5718D5F0.8010501@oracle.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain;
 charset=UTF-8
Subject: Re: [RFC v1 3/4] x86, boot: Implement ASLR for kernel memory sections (x86_64)
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Thu, 21 Apr 2016 08:46:27 -0700
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Thomas Garnier <thgarnie@google.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@suse.de>, Andy Lutomirski <luto@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Kees Cook <keescook@chromium.org>, Stephen Smalley <sds@tycho.nsa.gov>,
        Seth Jennings <sjennings@variantweb.net>,
        Kefeng Wang <wangkefeng.wang@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Toshi Kani <toshi.kani@hpe.com>,
        Alexander Kuleshov <kuleshovmail@gmail.com>,
        Alexander Popov <alpopov@ptsecurity.com>,
        Joerg Roedel <jroedel@suse.de>, Dave Young <dyoung@redhat.com>,
        Baoquan He <bhe@redhat.com>, Dave Hansen <dave.hansen@linux.intel.com>,
        Mark Salter <msalter@redhat.com>
CC: x86@kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        gthelen@google.com, kernel-hardening@lists.openwall.com
Message-ID: <9AF9DCC7-8FC4-4A93-B75A-C07B8CD9023A@zytor.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1213
Lines: 36

On April 21, 2016 6:30:24 AM PDT, Boris Ostrovsky <boris.ostrovsky@oracle.com> wrote:
>
>
>On 04/15/2016 06:03 PM, Thomas Garnier wrote:
>> +void __init kernel_randomize_memory(void)
>> +{
>> +	size_t i;
>> +	unsigned long addr = memory_rand_start;
>> +	unsigned long padding, rand, mem_tb;
>> +	struct rnd_state rnd_st;
>> +	unsigned long remain_padding = memory_rand_end - memory_rand_start;
>> +
>> +	if (!kaslr_enabled())
>> +		return;
>> +
>> +	/* Take the additional space when Xen is not active. */
>> +	if (!xen_domain())
>> +		page_offset_base -= __XEN_SPACE;
>
>This should be !xen_pv_domain(). Xen HVM guests are no different from 
>bare metal as far as address ranges are concerned. (Technically it's 
>probably !xen_pv_domain() && !xen_pvh_domain() but we can ignore PVH
>for 
>now since it is being replaced by an HVM-type guest)
>
>Having said that, I am not sure I understand why page_offset_base is 
>shifted. I thought 0xffff800000000000 - 0xffff87ffffffffff is not 
>supposed to be used by anyone, whether we are running under a
>hypervisor 
>or not.
>
>-boris

That range is reserved for the hypervisor use.
-- 
Sent from my Android device with K-9 Mail. Please excuse brevity and formatting.