+++ 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. I think I see how this can cause bugs, since if we're searching for seq_printf we want the real seq_printf and not the undef symbol from the livepatch module. But I thought we renamed these symbols with some .klp prefix? Or is the livepatch bug you're running into something else? 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
