kbuild: Fix modpost segfault

kbuild: Fix modpost segfault

commit 1c938663d58b5b2965976a6f54cc51b5d6f691aa upstream.

Alan <alan@clueserver.org> writes:

> program: /home/alan/GitTrees/linux-2.6-mid-ref/scripts/mod/modpost -o
> Module.symvers -S vmlinux.o
>
> Program received signal SIGSEGV, Segmentation fault.

It just hit me.
It's the offset calculation in reloc_location() which overflows:
        return (void *)elf->hdr + sechdrs[section].sh_offset +
               (r->r_offset - sechdrs[section].sh_addr);

E.g. for the first rodata r entry:
r->r_offset < sechdrs[section].sh_addr
and the expression in the parenthesis produces 0xFFFFFFE0 or something
equally wise.

Reported-by: Alan <alan@clueserver.org>
Signed-off-by: Krzysztof Hałasa <khc@pm.waw.pl>
Tested-by: Alan <alan@clueserver.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>