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SubjectRe: [PATCH] hibernation: on 32-bit x86, disabled in favor of KASLR
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On 23.03.2017 03:27, Kees Cook wrote:
> This is a modified revert of commit 65fe935dd238 ("x86/KASLR, x86/power:
> Remove x86 hibernation restrictions"), since it appears that 32-bit
> hibernation still can't support KASLR. 64-bit is fine. Since people have
> been running with KASLR by default on 32-bit since v4.8, this disables
> hibernation (with a warning). Booting with "nokaslr" will disable KASLR
> and enable hibernation.
>
> Reported-by: Evgenii Shatokhin <eugene.shatokhin@yandex.ru>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Cc: stable@vger.kernel.org # v4.8+

The patch does not work as intended on my system, unfortunately.

I tried the mainline kernel v4.11-rc3 and added this patch. With
"nokaslr" in the kernel command line, the system fails to hibernate. It
complains this way in the log:

<...>
kernel: PM: writing image.
kernel: PM: Cannot find swap device, try swapon -a.
kernel: PM: Cannot get swap writer
kernel: PM: Basic memory bitmaps freed
kernel: Restarting tasks ... done.
systemd[1]: Time has been changed
systemd[3948]: Time has been changed
systemd[14825]: Time has been changed
systemd[1]: systemd-hibernate.service: main process exited, code=exited,
status=1/FAILURE
systemd[1]: Failed to start Hibernate.
<...>

The swap device (swap file, actually) is available, however:
-------------
# swapon -s
Filename Type Size Used Priority
/swap file 6297596 0 -1
-------------

I built the same kernel without this patch then, added "nokaslr" in the
kernel command line again, and the system hibernates and resumes fine.

> ---
> Documentation/admin-guide/kernel-parameters.txt | 5 +++++
> arch/x86/boot/compressed/kaslr.c | 3 +++
> kernel/power/hibernate.c | 18 +++++++++++++++++-
> 3 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 2ba45caabada..6f899c7f587d 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1725,6 +1725,11 @@
> kernel and module base offset ASLR (Address Space
> Layout Randomization).
>
> + On 32-bit x86 with CONFIG_HIBERNATION, hibernation
> + is disabled if KASLR is enabled. If "nokaslr" is
> + specified, KASLR will be diabled and hibernation
> + will be enabled.
> +
> keepinitrd [HW,ARM]
>
> kernelcore= [KNL,X86,IA-64,PPC]
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 8b7c9e75edcb..b694af45f1e0 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -572,6 +572,9 @@ void choose_random_location(unsigned long input,
> return;
> }
>
> + if (IS_ENABLED(CONFIG_X86_32) && IS_ENABLED(CONFIG_HIBERNATION))
> + warn("KASLR active: hibernation disabled on 32-bit x86.");
> +
> boot_params->hdr.loadflags |= KASLR_FLAG;
>
> /* Prepare to add new identity pagetables on demand. */
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index a8b978c35a6a..1d8f1fe1b7f4 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -37,9 +37,14 @@
> #include "power.h"
>
>
> -static int nocompress;
> +#if defined(CONFIG_X86_32) && defined(CONFIG_RANDOMIZE_BASE)
> +static int noresume = 1;
> +static int nohibernate = 1;
> +#else
> static int noresume;
> static int nohibernate;
> +#endif
> +static int nocompress;
> static int resume_wait;
> static unsigned int resume_delay;
> static char resume_file[256] = CONFIG_PM_STD_PARTITION;
> @@ -1194,3 +1199,14 @@ __setup("hibernate=", hibernate_setup);
> __setup("resumewait", resumewait_setup);
> __setup("resumedelay=", resumedelay_setup);
> __setup("nohibernate", nohibernate_setup);
> +
> +/* Allow hibernation to be disabled in favor of KASLR on 32-bit x86. */
> +#if defined(CONFIG_X86_32) && defined(CONFIG_RANDOMIZE_BASE)
> +static int __init nokaslr_hibernate_setup(char *str)
> +{
> + noresume = 0;
> + nohibernate = 0;
> + return 1;
> +}
> +__setup("nokaslr", nokaslr_hibernate_setup);
> +#endif
>

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