* Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Wed, Apr 6, 2016 at 1:56 PM, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, Apr 6, 2016 at 1:17 PM, Pavel Machek <pavel@xxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
