Re: ppc64le STRICT_MODULE_RWX and livepatch apply_relocate_add() crashes

[Joe Lawrence <joe.lawrence@redhat.com>]

On 12/13/21 2:42 AM, Christophe Leroy wrote:
> 
> Hello Joe,
> 
> I'm implementing LIVEPATCH on PPC32 and I wanted to test with 
> STRICT_MODULE_RWX enabled so I took your branch as suggested, but I'm 
> getting the following errors on build. What shall I do ?
> 
>    CALL    scripts/checksyscalls.sh
>    CALL    scripts/atomic/check-atomics.sh
>    CHK     include/generated/compile.h
>    KLP     lib/livepatch/test_klp_convert1.ko
> klp-convert: section .rela.klp.module_relocs.test_klp_convert_mod length 
> beyond nr_entries
> 
> klp-convert: Unable to load user-provided sympos
> make[2]: *** [scripts/Makefile.modfinal:79: 
> lib/livepatch/test_klp_convert1.ko] Error 255
>    KLP     lib/livepatch/test_klp_convert2.ko
> klp-convert: section .rela.klp.module_relocs.test_klp_convert_mod length 
> beyond nr_entries
> 
> klp-convert: Unable to load user-provided sympos
> make[2]: *** [scripts/Makefile.modfinal:79: 
> lib/livepatch/test_klp_convert2.ko] Error 255
>    KLP     lib/livepatch/test_klp_convert_sections.ko
> klp-convert: section .rela.klp.module_relocs.test_klp_convert_mod length 
> beyond nr_entries
> 
> klp-convert: Unable to load user-provided sympos
> make[2]: *** [scripts/Makefile.modfinal:79: 
> lib/livepatch/test_klp_convert_sections.ko] Error 255
> make[2]: Target '__modfinal' not remade because of errors.
> make[1]: *** [scripts/Makefile.modpost:145: __modpost] Error 2
> make: *** [Makefile:1770: modules] Error 2
> 

Hi Christophe,

Interesting failure mode.  That's klp-convert complaining that it found
more relocations in a .klp.module_relocs.<objname> section than
expected, i.e. nr_entries = sec->size / sizeof(struct klp_module_reloc).

A few possibilities: the ELF sec->size was incorrectly set/read by
build/libelf (I doubt that).  Or maybe the layout/size of struct
klp_module_reloc is not consistent between kernel and userspace (I'm
more suspicious of this).

Can you post a copy of the build's symbols.klp and
lib/livepatch/test_klp_convert1.tmp.ko somewhere?  I should be able to
start debug with those files.

Thanks,
-- 
Joe