+++ Jessica Yu [04/06/18 10:05 +0200]:
+++ Josh Poimboeuf [02/06/18 12:32 -0500]:
Hi Jessica,
I found a bug:
[root@f25 ~]# modprobe livepatch-sample
[root@f25 ~]# grep ' u ' /proc/kallsyms
ffffffff81161080 u klp_enable_patch [livepatch_sample]
ffffffff81a01800 u __fentry__ [livepatch_sample]
ffffffff81161250 u klp_unregister_patch [livepatch_sample]
ffffffff81161870 u klp_register_patch [livepatch_sample]
ffffffff8131f0b0 u seq_printf [livepatch_sample]
Notice that livepatch modules' undefined symbols are showing up in
/proc/kallsyms. This can confuse klp_find_object_symbol() which can
cause subtle bugs in livepatch.
I stared at the module kallsyms code for a bit, but I don't see the bug.
Maybe it has something to do with how we save the symbol table in
copy_module_elf(). Any ideas?
Hi Josh!
This is because we preserve the entire symbol table for livepatch
modules, including the SHN_UNDEF symbols. IIRC, this is so that we can
still apply relocations properly with apply_relocate_add() after a
to-be-patched object is loaded. Normally we don't save these SHN_UNDEF
symbols for modules so they do not appear in /proc/kallsyms.
Hm, if having the full symtab in kallsyms is causing trouble, one
possibility would be to just have the module kallsyms code simply
skip/ignore undef symbols. That's what we technically do for normal
modules anyway (we normally cut undef syms out of the symtab). Haven't
tested this idea but does that sound like it'd help?
Thanks,
Jessica
--
To unsubscribe from this list: send the line "unsubscribe live-patching" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
