* Kees Cook <keesc...@chromium.org> wrote:
> On Wed, Apr 6, 2016 at 1:56 PM, Linus Torvalds
> <torva...@linux-foundation.org> wrote:
> > On Wed, Apr 6, 2016 at 1:17 PM, Pavel Machek <pa...@denx.de> wrote:
> >>
> >> Why is kASLR incompatible with hibernation? We can hibernate have
> >> 4.3 kernel resume hibernation image of 4.2 kernel (on x86-64, and I
> >> have patches for x86). Resuming kernel with different randomization
> >> does not look that much different...
> >
> > Oh, I'd absolutely prefer to just allow kaslr together with
> > hibernation if it actually works.
> >
> > Could the people who piped up to say that they actually use
> > hibernation just try passing in the "kaslr" command line option on
> > their machine, and see if it works for them? We could just remove the
> > "no kaslr with hibername" code - or at least limit it to 32-bit for
> > now..
> >
> > Because that would be lovely.
>
> This is where our original investigation of having them coexist ended:
> https://lkml.org/lkml/2014/6/15/180
>
> To quote Rafael Wysocki:
> > We're jumping from the boot kernel into the image kernel. The virtual
> > address
> > comes from the image kernel, but the boot kernel has to use it. The only
> > way
> > we can ensure that we'll jump to the right place is to pass the physical
> > address
> > in the header (otherwise we de facto assume that the virtual address of the
> > target page frame will be the same in both the boot and the image kernels).
> >
> > The missing piece is that the code in swsusp_arch_resume() sets up temporary
> > page tables to ensure that they won't be overwritten while copying the last
> > remaining image kernel pages to the right page frames (those page tables
> > have to be stored in page frames that are free from the kernel image
> > perspective).
> >
> > But if the kernel address space is randomized, set_up_temporary_mappings()
> > really should duplicate the existing layout instead of creating a new one
> > from
> > scratch. Otherwise, virtual addresses before set_up_temporary_mappings()
> > may
> > be different from the ones after it.
So as I suggested it in the previous mail, the right solution would be to pass
in
the randomization seed via a new kasl_seed=xyz boot option, and thus have the
same
addresses as prior hibernation.
That should make hibernation work as-is, with very little effort.
Two details I can think of:
1) the new option has to be hidden from /proc/cmdline, due to:
triton:~/tip> ll /proc/cmdline
-r--r--r-- 1 root root 0 Apr 6 23:45 /proc/cmdline
2)
another detail is that the new boot option has to be checked in
choose_kernel_location(), to make sure it's done at the right point during
bootup.
That's a good place to remove it from the boot options string as well.
Thanks,
Ingo
