Re: [PATCH] hibernation: on 32-bit x86, disabled in favor of KASLR

[Evgenii Shatokhin]

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@xxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # 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