Re: [RFC PATCH v4 2/6] module: preserve Elf information for livepatch modules

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

 	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);