Re: module: preserve Elf information for livepatch modules

[Jessica Yu]

+++ Petr Mladek [17/12/15 17:26 +0100]:
> On Mon 2015-11-30 23:21:15, Jessica Yu wrote:
> > For livepatch modules, copy Elf section, symbol, and string information
> > from the load_info struct in the module loader.
> >
> > Livepatch uses special relocation sections in order to be able to patch
> > modules that are not yet loaded, as well as apply patches to the kernel
> > when the addresses of symbols cannot be determined at compile time (for
> > example, when kaslr is enabled). Livepatch modules must preserve Elf
> > information such as section indices in order to apply the remaining
> > relocation sections at the appropriate time (i.e. when the target module
> > loads).
> >
> > Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
> > ---
> >  include/linux/module.h |  9 +++++
> >  kernel/module.c        | 98 ++++++++++++++++++++++++++++++++++++++++++++++++--
> >  2 files changed, 105 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index 3a19c79..9b46256 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -425,6 +425,14 @@ struct module {
> >
> >  	/* Notes attributes */
> >  	struct module_notes_attrs *notes_attrs;
> > +
> > +	/* Elf information (optionally saved) */
> > +	Elf_Ehdr *hdr;
> > +	Elf_Shdr *sechdrs;
> > +	char *secstrings;
> > +	struct {
> > +		unsigned int sym, str, mod, vers, info, pcpu;
> > +	} index;
> >  #endif
>
> I would hide this into a structure. It is 3 pointers and 6 integers
> that are mostly unused. I think about using a pointer to struct load_info
> here. We could set the unused stuff to zero and NULL.
>
> Any better idea how to share the definition with struct load_info
> is welcome.

Sure. If we want to encapsulate all this information, we can perhaps
replace this with a single pointer to a copy of load_info, and maybe
move the struct definition of load_info to module.h.

Jessica
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