livepatch: Disallow applying after an revert

livepatch: Disallow applying after an revert

On general this is unhealthy - as the payload's .bss (definitly)
or .data (maybe) will be modified once the payload is running.

Doing an revert and then re-applying the payload with a non-pristine
.bss or .data can lead to unforseen consequences (.bss are assumed
to always contain zero value but now they may have a different value).

There is one exception - if the payload contains only one .data section
- the .livepatch.funcs, then it is OK to re-apply an revert.
We detect this rather simply (if there is one RW section and its name
is .livepatch.funcs) - but the payload may have many other RW sections
that are not used at all (such as .bss or .data sections with zero
length). To not account those we also ignore sections with sh_size
being zero.

Reviewed-by: Jan Beulich <jbeulich@suse.com>
Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>