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

[Boris Ostrovsky]

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