Hey Kees, Thomas, On Wed, Jun 22, 2016 at 10:05:51AM -0700, Kees Cook wrote: > On Wed, Jun 22, 2016 at 8:59 AM, Thomas Garnier <thgar...@google.com> wrote: > > On Wed, Jun 22, 2016 at 5:47 AM, Jason Cooper <ja...@lakedaemon.net> wrote: > >> Hey Kees, > >> > >> On Tue, Jun 21, 2016 at 05:46:57PM -0700, Kees Cook wrote: > >>> Notable problems that needed solving: > >> ... > >>> - Reasonable entropy is needed early at boot before get_random_bytes() > >>> is available. > >> > >> This series is targetting x86, which typically has RDRAND/RDSEED > >> instructions. Are you referring to other arches? Older x86? Also, > >> isn't this the same requirement for base address KASLR? > >> > >> Don't get me wrong, I want more diverse entropy sources available > >> earlier in the boot process as well. :-) I'm just wondering what's > >> different about this series vs base address KASLR wrt early entropy > >> sources. > >> > > > > I think Kees was referring to the refactor I did to get the similar > > entropy generation than KASLR module randomization. Our approach was > > to provide best entropy possible even if you have an older processor > > or under virtualization without support for these instructions. > > Unfortunately common on companies with a large number of older > > machines. > > Right, the memory offset KASLR uses the same routines as the kernel > base KASLR. The issue is with older x86 systems, which continue to be > very common.
We have the same issue in embedded. :-( Compounded by the fact that there is no rand instruction (at least not on ARM). So, even if there's a HW-RNG, you can't access it until the driver is loaded. This is compounded by the fact that most systems deployed today have bootloaders a) without hw-rng drivers, b) without dtb editing, and c) without dtb support at all. My current thinking is to add a devicetree property "userspace,random-seed" <address, len>. This way, existing, deployed boards can append a dtb to a modern kernel with the property set. The factory bootloader then only needs to amend its boot scripts to read random-seed from the fs to the given address. Modern systems that receive a seed from the bootloader via the random-seed property (typically from the hw-rng) can mix both sources for increased resilience. Unfortunately, I'm not very familiar with the internals of x86 bootstrapping. Could GRUB be scripted to do a similar task? How would the address and size of the seed be passed to the kernel? command line? thx, Jason.
