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

[H. Peter Anvin]

On April 21, 2016 6:30:24 AM PDT, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> 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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