[RFC PATCH 2/5] module: save load_info for livepatch modules

[Jessica Yu]

In livepatch modules, preserve section, symbol, string information from
the load_info struct in the module loader. This information is used to
patch modules that are not loaded in memory yet; specifically it is used
to resolve remaining symbols and write relocations when the target
module loads.

Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
---
 include/linux/module.h  | 25 +++++++++++++++++++++++++
 kernel/livepatch/core.c | 17 +++++++++++++++++
 kernel/module.c         | 36 ++++++++++++++++++++++--------------
 3 files changed, 64 insertions(+), 14 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 3a19c79..c8680b1 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -36,6 +36,20 @@ struct modversion_info {
 	char name[MODULE_NAME_LEN];
 };
 
+struct load_info {
+	Elf_Ehdr *hdr;
+	unsigned long len;
+	Elf_Shdr *sechdrs;
+	char *secstrings, *strtab;
+	unsigned long symoffs, stroffs;
+	struct _ddebug *debug;
+	unsigned int num_debug;
+	bool sig_ok;
+	struct {
+		unsigned int sym, str, mod, vers, info, pcpu;
+	} index;
+};
+
 struct module;
 
 struct module_kobject {
@@ -462,6 +476,8 @@ struct module {
 
 #ifdef CONFIG_LIVEPATCH
 	bool klp_alive;
+	/* save info to patch to-be-loaded modules */
+	struct load_info *info;
 #endif
 
 #ifdef CONFIG_MODULE_UNLOAD
@@ -635,6 +651,15 @@ static inline bool module_requested_async_probing(struct module *module)
 	return module && module->async_probe_requested;
 }
 
+#ifdef CONFIG_LIVEPATCH
+extern void klp_prepare_patch_module(struct module *mod,
+				     struct load_info *info);
+extern int
+apply_relocate_add(Elf64_Shdr *sechdrs, const char *strtab,
+		   unsigned int symindex, unsigned int relsec,
+		   struct module *me);
+#endif
+
 #else /* !CONFIG_MODULES... */
 
 /* Given an address, look for it in the exception tables. */
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 6e53441..087a8c7 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -1001,6 +1001,23 @@ static struct notifier_block klp_module_nb = {
 	.priority = INT_MIN+1, /* called late but before ftrace notifier */
 };
 
+/*
+ * Save necessary information from info in order to be able to
+ * patch modules that might be loaded later
+ */
+void klp_prepare_patch_module(struct module *mod, struct load_info *info)
+{
+	Elf_Shdr *symsect;
+
+	symsect = info->sechdrs + info->index.sym;
+	/* update sh_addr to point to symtab */
+	symsect->sh_addr = (unsigned long)info->hdr + symsect->sh_offset;
+
+	mod->info = kzalloc(sizeof(*info), GFP_KERNEL);
+	memcpy(mod->info, info, sizeof(*info));
+
+}
+
 static int __init klp_init(void)
 {
 	int ret;
diff --git a/kernel/module.c b/kernel/module.c
index 8f051a1..8ae3ca5 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -318,20 +318,6 @@ int unregister_module_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_module_notifier);
 
-struct load_info {
-	Elf_Ehdr *hdr;
-	unsigned long len;
-	Elf_Shdr *sechdrs;
-	char *secstrings, *strtab;
-	unsigned long symoffs, stroffs;
-	struct _ddebug *debug;
-	unsigned int num_debug;
-	bool sig_ok;
-	struct {
-		unsigned int sym, str, mod, vers, info, pcpu;
-	} index;
-};
-
 /* We require a truly strong try_module_get(): 0 means failure due to
    ongoing or failed initialization etc. */
 static inline int strong_try_module_get(struct module *mod)
@@ -2137,6 +2123,11 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
 			       (long)sym[i].st_value);
 			break;
 
+#ifdef CONFIG_LIVEPATCH
+		case SHN_LIVEPATCH:
+			break;
+#endif
+
 		case SHN_UNDEF:
 			ksym = resolve_symbol_wait(mod, info, name);
 			/* Ok if resolved.  */
@@ -2185,6 +2176,11 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
 		if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
 			continue;
 
+#ifdef CONFIG_LIVEPATCH
+		if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
+			continue;
+#endif
+
 		if (info->sechdrs[i].sh_type == SHT_REL)
 			err = apply_relocate(info->sechdrs, info->strtab,
 					     info->index.sym, i, mod);
@@ -3530,8 +3526,20 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	if (err < 0)
 		goto bug_cleanup;
 
+#ifdef CONFIG_LIVEPATCH
+	/*
+	 * Save sechdrs, indices, and other data from info
+	 * in order to patch to-be-loaded modules.
+	 * Do not call free_copy() for livepatch modules.
+	 */
+	if (get_modinfo((struct load_info *)info, "livepatch"))
+		klp_prepare_patch_module(mod, info);
+	else
+		free_copy(info);
+#else
 	/* Get rid of temporary copy. */
 	free_copy(info);
+#endif
 
 	/* Done! */
 	trace_module_load(mod);
-- 
2.4.3

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