W/the relocation information, we can pick the virtual address to load at independent from the physical load address.
On Mon, Apr 15, 2013 at 2:41 PM, Kees Cook <keesc...@chromium.org> wrote: > On Mon, Apr 15, 2013 at 2:25 PM, H. Peter Anvin <h...@zytor.com> wrote: >> On 04/15/2013 02:06 PM, Eric Northup wrote: >>> On Sat, Apr 13, 2013 at 8:06 PM, H. Peter Anvin <h...@zytor.com> wrote: >>>> On 04/13/2013 05:37 PM, Yinghai Lu wrote: >>>>> >>>>> so decompress code position is changed? >>>>> >>>>> You may push out bss and other data area of run-time kernel of limit >>>>> that boot loader >>>>> chose according to setup_header.init_size. >>>>> aka that make those area overlap with ram hole or other area like >>>>> boot command line or initrd.... >>>>> >>>> >>>> Is there a strong reason to randomize the physical address on 64 bits >>>> (and if so, shouldn't we do it right?) >>> >>> The reason to randomize the physical address is because of the kernel >>> direct mapping range -- a predictable-to-attackers physical address >>> implies a predictable-to-attackers virtual address. >>> >>> It had seemed to me like changing the virtual base of the direct >>> mapping would be much more involved than physically relocating the >>> kernel, but better suggestions would be most welcome :-) >>> >> >> You seem to be missing something here... >> >> There are *two* mappings in 64-bit mode. Physically, if you're going to >> randomize you might as well randomize over the entire range... except >> not too far down (on either 32 or 64 bit mode)... in particular, you >> don't want to drop below 16 MiB if you can avoid it. >> >> On 64 bits, there is no reason the virtual address has to be randomized >> the same way. > > Aren't we bound by the negative 2GB addressing due to -mcmodel=kernel? > > -Kees > > -- > Kees Cook > Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
