On Wed 2016-02-03 20:11:07, Jessica Yu wrote: > For livepatch modules, copy Elf section, symbol, and string information > from the load_info struct in the module loader. Persist copies of the > original symbol table and string table. > > Livepatch manages its own relocation sections in order to reuse module > loader code to write relocations. Livepatch modules must preserve Elf > information such as section indices in order to apply livepatch relocation > sections using the module loader's apply_relocate_add() function. > > In order to apply livepatch relocation sections, livepatch modules must > keep a complete copy of their original symbol table in memory. Normally, a > stripped down copy of a module's symbol table (containing only "core" > symbols) is made available through module->core_symtab. But for livepatch > modules, the symbol table copied into memory on module load must be exactly > the same as the symbol table produced when the patch module was compiled. > This is because the relocations in each livepatch relocation section refer > to their respective symbols with their symbol indices, and the original > symbol indices (and thus the symtab ordering) must be preserved in order > for apply_relocate_add() to find the right symbol. > > diff --git a/kernel/module.c b/kernel/module.c > index 71c77ed..9c16eb2 100644 > --- a/kernel/module.c > +++ b/kernel/module.c > @@ -3222,6 +3331,12 @@ static noinline int do_init_module(struct module *mod) > */ > current->flags &= ~PF_USED_ASYNC; > > +#ifdef CONFIG_KALLSYMS > + /* Make symtab and strtab available prior to module init call */ > + mod->num_symtab = mod->core_num_syms; > + mod->symtab = mod->core_symtab; > + mod->strtab = mod->core_strtab; > +#endif This should be done with module_mutex. Otherwise, it looks racy at least against module_kallsyms_on_each_symbol(). BTW: I wonder why even the original code is not racy for example against module_get_kallsym. It is called without the mutex. This code sets the number of entries before the pointer to the entries. Note that the module is in the list even in the UNFORMED state. > do_mod_ctors(mod); > /* Start the module */ > if (mod->init != NULL) > @@ -3266,11 +3381,6 @@ static noinline int do_init_module(struct module *mod) > /* Drop initial reference. */ > module_put(mod); > trim_init_extable(mod); > -#ifdef CONFIG_KALLSYMS > - mod->num_symtab = mod->core_num_syms; > - mod->symtab = mod->core_symtab; > - mod->strtab = mod->core_strtab; > -#endif > mod_tree_remove_init(mod); > disable_ro_nx(&mod->init_layout); > module_arch_freeing_init(mod); In each case, it was called with the mutex here. Best Regards, Petr -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
