linux-imx

PM / hibernate: Verify the consistent of e820 memory map by md5 digest

On some platforms, there is occasional panic triggered when
trying to resume from hibernation, a typical panic looks like:

"BUG: unable to handle kernel paging request at ffff880085894000
IP: [<ffffffff810c5dc2>] load_image_lzo+0x8c2/0xe70"

Investigation carried out by Lee Chun-Yi shows that this is because
e820 map has been changed by BIOS across hibernation, and one
of the page frames from suspend kernel is right located in restore
kernel's unmapped region, so panic comes out when accessing unmapped
kernel address.

In order to expose this issue earlier, the md5 hash of e820 map
is passed from suspend kernel to restore kernel, and the restore
kernel will terminate the resume process once it finds the md5
hash are not the same.

As the format of image header has been modified, the magic number
should also be adjusted as kernels with the same RESTORE_MAGIC have
to use the same header format and interpret all of the fields in
it in the same way.

If the suspend kernel is built without md5 support, and the restore
kernel has md5 support, then the latter will bypass the check process.
Vice versa the restore kernel will bypass the check if it does not
support md5 operation.

Note:
1. Without this patch applied, it is possible that BIOS has
   provided an inconsistent memory map, but the resume kernel is still
   able to restore the image anyway(e.g, E820_RAM region is the superset
   of the previous one), although the system might be unstable. So this
   patch tries to treat any inconsistent e820 as illegal.

2. Another case is, this patch replies on comparing the e820_saved, but
   currently the e820_save might not be strictly the same across
   hibernation, even if BIOS has provided consistent e820 map - In
   theory mptable might modify the BIOS-provided e820_saved dynamically
   in early_reserve_e820_mpc_new, which would allocate a buffer from
   E820_RAM, and marks it from E820_RAM to E820_RESERVED).
   This is a potential and rare case we need to deal with in OS in
   the future.

Suggested-by: Pavel Machek <pavel@ucw.cz>
Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Reviewed-by: Lee, Chun-Yi <jlee@suse.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>