On Wednesday, September 29, 2010, H. Peter Anvin wrote:
> On 09/28/2010 04:12 PM, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@xxxxxxx>
> >
> > On x86_64 the configuration and version of the kernel that
> > hibernates and creates a system image may be different from the
> > configuration and version of the boot kernel that loads the image.
> > So long as both these kernels are built with the same value of
> > RESTORE_MAGIC, the image created by one of them should be
> > successfully loaded and restored by the other one.
> >
> > It wasn't necessary to modify RESTORE_MAGIC in the past, but now
> > that we are adding compression to the in-kernel hibernate code,
> > change the value of RESTORE_MAGIC so that earlier kernels don't
> > try to load compressed images they can't handle.
> >
> > Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
> > ---
> > arch/x86/power/hibernate_64.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > Index: linux-2.6/arch/x86/power/hibernate_64.c
> > ===================================================================
> > --- linux-2.6.orig/arch/x86/power/hibernate_64.c
> > +++ linux-2.6/arch/x86/power/hibernate_64.c
> > @@ -137,7 +137,7 @@ struct restore_data_record {
> > unsigned long magic;
> > };
> >
> > -#define RESTORE_MAGIC 0x0123456789ABCDEFUL
> > +#define RESTORE_MAGIC 0x0123456789ABCDF0UL
> >
>
> Two issues with this:
>
> a) shouldn't we only set this when the image is actually compressed?
Well, in fact, this is a workaround, because the compression happens in a
different layer. However, that other layer doesn't have any compatibility
checks (at least on x86-64), other than seeing that the image metadata
don't make sense at one point.
> b) using systematic magics like this is pessimal in terms of collision
> avoidance. It's much better to use a true random number.
>
> Hence, I propose:
>
> : anacreon 95 ; ranpwd -xc 16
> 0x4ddedd3236f1e6e1
Fine with me, although I don't expect it will be necessary to do that in
the future.
Thanks,
Rafael
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