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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