* Ingo Molnar <[email protected]> wrote:
>
> * Kees Cook <[email protected]> wrote:
>
> > On Wed, Apr 6, 2016 at 1:56 PM, Linus Torvalds
> > <[email protected]> wrote:
> > > On Wed, Apr 6, 2016 at 1:17 PM, Pavel Machek <[email protected]> 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.
... and I missed the biggest complication: to solve the chicken and egg problem
with software_resume() running very late during bootup, software_resume()
should
probably kexec() the original kernel image, this time with the kaslr seed set
in
the boot parameters.
So it's two bootups...
Thanks,
Ingo
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