Re: [RFC v1 3/4] x86, boot: Implement ASLR for kernel memory sections (x86_64)

Thomas Garnier
2016-04-21T15:52:05Z

On Thu, Apr 21, 2016 at 8:46 AM, H. Peter Anvin <hpa@zytor.com> wrote:
> 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.

I know, I thought I could use it if no hypervisor was used but might
introduce problems in the future so I will remove it for the next
iteration.

> --
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