Date: Wed, 6 Apr 2016 14:25:12 -0700 From: Kees Cook <keescook@...omium.org> To: Linus Torvalds <torvalds@...ux-foundation.org>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com> Cc: 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 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. -Kees -- Kees Cook Chrome OS & Brillo Security
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