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Re: [PATCH] Prefer kASLR over Hibernation

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Hi Kees,

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).


> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index fca9254280ee..be5041354b1e 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1159,6 +1164,13 @@ static int __init kaslr_nohibernate_setup(char *str)
>  	return nohibernate_setup(str);
>  }
>  
> +static int __init nokaslr_hibernate_setup(char *str)
> +{
> +	noresume = 0;
> +	nohibernate = 0;
> +	return 1;
> +}
> +
>  static int __init page_poison_nohibernate_setup(char *str)
>  {
>  #ifdef CONFIG_PAGE_POISONING_ZERO
> @@ -1183,4 +1195,5 @@ __setup("resumewait", resumewait_setup);
>  __setup("resumedelay=", resumedelay_setup);
>  __setup("nohibernate", nohibernate_setup);
>  __setup("kaslr", kaslr_nohibernate_setup);
> +__setup("nokaslr", nokaslr_hibernate_setup);

So one or the other option has to be specified at boot?

The kASLR patches for arm64 in v4.6-rc1 enable kASLR at boot if you chose to
select it at compile time. I guess this patch is preparation for doing the same
on x86?

I didn't hit this kaslr_nohibernate_setup() call during testing because of the
on by default behaviour. Is it worth exposing this via Kconfig? Something like:
ARCH_RANDOMIZE_BASE_DEFAULT_ON ?


Thanks,

James

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Thread

[PATCH] Prefer kASLR over Hibernation Kees Cook <keescook@chromium.org> - 2016-04-06 21:50 +0200
  Re: [PATCH] Prefer kASLR over Hibernation Pavel Machek <pavel@denx.de> - 2016-04-06 22:20 +0200
    Re: [PATCH] Prefer kASLR over Hibernation Linus Torvalds <torvalds@linux-foundation.org> - 2016-04-06 23:00 +0200
      Re: [PATCH] Prefer kASLR over Hibernation Kees Cook <keescook@chromium.org> - 2016-04-06 23:30 +0200
        Re: [PATCH] Prefer kASLR over Hibernation Ingo Molnar <mingo@kernel.org> - 2016-04-06 23:50 +0200
          Re: [PATCH] Prefer kASLR over Hibernation Ingo Molnar <mingo@kernel.org> - 2016-04-07 00:00 +0200
            Re: [PATCH] Prefer kASLR over Hibernation "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-07 00:40 +0200
              Re: [PATCH] Prefer kASLR over Hibernation Ingo Molnar <mingo@kernel.org> - 2016-04-07 03:00 +0200
  Re: [PATCH] Prefer kASLR over Hibernation "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-06 23:50 +0200
    Re: [PATCH] Prefer kASLR over Hibernation Ingo Molnar <mingo@kernel.org> - 2016-04-07 00:00 +0200
      Re: [PATCH] Prefer kASLR over Hibernation "Rafael J. Wysocki" <rafael@kernel.org> - 2016-04-07 00:10 +0200
        Re: [PATCH] Prefer kASLR over Hibernation Kees Cook <keescook@chromium.org> - 2016-04-07 00:20 +0200
          Re: [PATCH] Prefer kASLR over Hibernation Paul Bolle <pebolle@tiscali.nl> - 2016-04-07 00:50 +0200
          Re: [PATCH] Prefer kASLR over Hibernation Ingo Molnar <mingo@kernel.org> - 2016-04-07 02:10 +0200
  Re: [PATCH] Prefer kASLR over Hibernation James Morse <james.morse@arm.com> - 2016-04-11 10:10 +0200
    Re: [PATCH] Prefer kASLR over Hibernation Kees Cook <keescook@chromium.org> - 2016-04-11 20:10 +0200
      Re: [PATCH] Prefer kASLR over Hibernation Geert Uytterhoeven <geert@linux-m68k.org> - 2016-04-11 20:30 +0200
        Re: [PATCH] Prefer kASLR over Hibernation Kees Cook <keescook@chromium.org> - 2016-04-11 20:50 +0200
      Re: [PATCH] Prefer kASLR over Hibernation James Morse <james.morse@arm.com> - 2016-04-12 20:00 +0200

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