Date: Tue, 12 Apr 2016 18:51:06 +0100 From: James Morse <james.morse@....com> To: Kees Cook <keescook@...omium.org> CC: Linus Torvalds <torvalds@...ux-foundation.org>, 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>, "x86@...nel.org" <x86@...nel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>, Borislav Petkov <bp@...e.de>, Andy Lutomirski <luto@...nel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, linux-pm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH] Prefer kASLR over Hibernation On 11/04/16 19:03, Kees Cook wrote: > On Mon, Apr 11, 2016 at 1:00 AM, James Morse <james.morse@....com> wrote: >> On 06/04/16 20:44, Kees Cook wrote: >>> When building with both CONFIG_HIBERNATION and CONFIG_RANDOMIZE_BASE, >>> one or the other must be chosen at boot-time. Until now, hibernation >>> was selected when no choice was made on the command line. >>> >>> To make the security benefits of kASLR more widely available to end >>> users (since the use of hibernation is becoming more rare and kASLR, >>> already available on x86, will be available on arm64 and MIPS soon), >>> this changes the default to preferring kASLR over hibernation. Users >>> wanting hibernation can turn off kASLR by adding "nokaslr" to the kernel >>> command line. >> >> While hibernate isn't yet merged for arm64, it does work with kASLR in v4.6-rc*, >> it would be a shame to have to choose at boot time, (but that's my problem to >> fix if/when its merged). > > Ah, interesting, so they work together on arm64? (i.e. you've actually > tested a boot loader that provides the seed for kASLR to operate?) Almost: due to a lack of firmware support I hacked the efi stub to read a 'seed' from a system counter. To check it works I printed the address of 'panic' out during boot: > [ 0.353712] DEBUG: &panic == ffffff960819a4e8 Then hibernated, and powered the board back on, the resume kernel gives: > [ 0.353528] DEBUG: &panic == ffffff840819a4e8 But after it has restored the hibernate image, I can dig in /proc/kallsyms to see the original value: > root@...alhost:~# cat /proc/kallsyms | grep "T panic" > ffffff960819a4e8 T panic > Maybe RANDOMIZE_BASE_DEFAULT (default to y) and if x86 && hibernation, > select =n. and use that for selecting it? Looks good to me. Thanks, James
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