Re: [PATCH][v12] PM / hibernate: Verify the consistent of e820 memory map by md5 digest

joeyli
2016-10-22T03:03:19Z

Hi Chen Yu,

On Thu, Oct 20, 2016 at 04:14:52PM +0800, Chen Yu wrote:
> 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>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> Cc: Pavel Machek <pavel@ucw.cz>
> Cc: Lee Chun-Yi <jlee@suse.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Len Brown <len.brown@intel.com>
> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>

Please feel free to add:
Reviewed-by: Lee, Chun-Yi <jlee@suse.com>

> ---
> v12:
> - Adding more user-friendly warnings when md5 confliction
> is detected.
> Use the actual e820_save size instead of the whole struct e820map
> to generate the md5.
> Use AHASH_REQUEST_ON_STACK as suggested by Denys Vlasenko.

Thanks
Joey Lee