Date: Wed, 6 Apr 2016 23:52:40 +0200 From: Ingo Molnar <mingo@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Pavel Machek <pavel@...x.de>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Matt Redfearn <matt.redfearn@...tec.com>, Yves-Alexis Perez <corsac@...ian.org>, Emrah Demir <ed@...sec.com>, Jonathan Corbet <corbet@....net>, the arch/x86 maintainers <x86@...nel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>, Borislav Petkov <bp@...e.de>, Andy Lutomirski <luto@...nel.org>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH] Prefer kASLR over Hibernation * Ingo Molnar <mingo@...nel.org> wrote: > > * Kees Cook <keescook@...omium.org> wrote: > > > On Wed, Apr 6, 2016 at 1:56 PM, Linus Torvalds > > <torvalds@...ux-foundation.org> wrote: > > > On Wed, Apr 6, 2016 at 1:17 PM, Pavel Machek <pavel@...x.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. ... 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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