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

H. Peter Anvin
2016-04-21T15:54:47Z

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.
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