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Date: Thu, 21 Apr 2016 09:30:24 -0400
From: Boris Ostrovsky <boris.ostrovsky@...cle.com>
To: Thomas Garnier <thgarnie@...gle.com>, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...e.de>, Andy Lutomirski <luto@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kees Cook <keescook@...omium.org>, Stephen Smalley <sds@...ho.nsa.gov>,
        Seth Jennings
 <sjennings@...iantweb.net>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Toshi Kani <toshi.kani@....com>,
        Alexander Kuleshov
 <kuleshovmail@...il.com>,
        Alexander Popov <alpopov@...ecurity.com>,
        Joerg Roedel <jroedel@...e.de>, Dave Young <dyoung@...hat.com>,
        Baoquan He <bhe@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
        Mark Salter <msalter@...hat.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        gthelen@...gle.com, kernel-hardening@...ts.openwall.com
Subject: Re: [RFC v1 3/4] x86, boot: Implement ASLR for kernel memory sections
 (x86_64)



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


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