Re: [PATCH 6/6] x86: kaslr: relocate base offset at boot

[Kees Cook]

On Mon, Apr 15, 2013 at 3:00 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> On Mon, Apr 15, 2013 at 2:46 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>> On 04/15/2013 02:41 PM, Kees Cook wrote:
>
>> Please read what I wrote.
>>
>> The 2 GB limit is for the *virtual* mapping.
>>
>> The *physical* mapping, where it lands in RAM, is completely
>> independent, and if you're going to randomize the latter, there is no
>> reason it has to match the former.  Instead, randomize it freely.
>>
>> That is different from the i386 kernel which runs at its
>> physical-mapping address.
>>
>> Incidentally, for performance reasons please avoid locating the kernel
>> below CONFIG_PHYSICAL_ADDRESS if possible.
>>
>> Also make sure your code works with more than 128 e820 entries.
>
> also do not overlap with boot_param, command_line, and initrd.
>
> and need to double check setup_header.init_size to make sure bss and
> etc will not
> fall into memory hole or reserved area in e820.
>
> also may need to setup page table for target position as bootloader may only
> has ident mapping only for loaded bzImage 64 areas.
>
> looks you are trying redo the work for bootloader to pick loaded phys addr.

aslr.S's select_aslr_address uses z_extract_offset as the upper bound.

-Kees

--
Kees Cook
Chrome OS Security
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