[RFC PATCH 3/5] livepatch: reuse module loader code to write relocations

[Jessica Yu]

Reuse module loader code to write relocations, thereby eliminating the
need for architecture specific code in livepatch. Namely, we reuse
apply_relocate_add() in the module loader to write relocs instead of
duplicating functionality in livepatch's klp_write_module_reloc(). To
apply relocation sections, remaining SHN_LIVEPATCH symbols referenced by
relocs are resolved and then apply_relocate_add() is called to apply
those relocations.

Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
---
 include/linux/livepatch.h | 11 ++++--
 include/linux/module.h    |  6 ++++
 kernel/livepatch/core.c   | 89 +++++++++++++++++++++++++++++------------------
 3 files changed, 70 insertions(+), 36 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 31db7a0..601e892 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -85,7 +85,7 @@ struct klp_reloc {
 /**
  * struct klp_object - kernel object structure for live patching
  * @name:	module name (or NULL for vmlinux)
- * @relocs:	relocation entries to be applied at load time
+ * @reloc_secs:	relocation sections to be applied at load time
  * @funcs:	function entries for functions to be patched in the object
  * @kobj:	kobject for sysfs resources
  * @mod:	kernel module associated with the patched object
@@ -95,7 +95,7 @@ struct klp_reloc {
 struct klp_object {
 	/* external */
 	const char *name;
-	struct klp_reloc *relocs;
+	struct list_head reloc_secs;
 	struct klp_func *funcs;
 
 	/* internal */
@@ -129,6 +129,13 @@ struct klp_patch {
 #define klp_for_each_func(obj, func) \
 	for (func = obj->funcs; func->old_name; func++)
 
+struct klp_reloc_sec {
+	unsigned int index;
+	char *name;
+	char *objname;
+	struct list_head list;
+};
+
 int klp_register_patch(struct klp_patch *);
 int klp_unregister_patch(struct klp_patch *);
 int klp_enable_patch(struct klp_patch *);
diff --git a/include/linux/module.h b/include/linux/module.h
index c8680b1..3c34eb8 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -793,9 +793,15 @@ extern int module_sysfs_initialized;
 #ifdef CONFIG_DEBUG_SET_MODULE_RONX
 extern void set_all_modules_text_rw(void);
 extern void set_all_modules_text_ro(void);
+extern void
+set_page_attributes(void *start, void *end,
+		    int (*set)(unsigned long start, int num_pages));
 #else
 static inline void set_all_modules_text_rw(void) { }
 static inline void set_all_modules_text_ro(void) { }
+static inline void
+set_page_attributes(void *start, void *end,
+		    int (*set)(unsigned long start, int num_pages)) { }
 #endif
 
 #ifdef CONFIG_GENERIC_BUG
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 087a8c7..26c419f 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -28,6 +28,8 @@
 #include <linux/list.h>
 #include <linux/kallsyms.h>
 #include <linux/livepatch.h>
+#include <linux/elf.h>
+#include <asm/cacheflush.h>
 
 /**
  * struct klp_ops - structure for tracking registered ftrace ops structs
@@ -281,46 +283,54 @@ static int klp_find_external_symbol(struct module *pmod, const char *name,
 }
 
 static int klp_write_object_relocations(struct module *pmod,
-					struct klp_object *obj)
+					struct klp_object *obj,
+					struct klp_patch *patch)
 {
-	int ret;
-	struct klp_reloc *reloc;
+	int relindex, num_relas;
+	int i, ret = 0;
+	unsigned long addr;
+	unsigned int bind;
+	char *symname;
+	struct klp_reloc_sec *reloc_sec;
+	struct load_info *info;
+	Elf_Rela *rela;
+	Elf_Sym *sym, *symtab;
+	Elf_Shdr *symsect;
 
 	if (WARN_ON(!klp_is_object_loaded(obj)))
 		return -EINVAL;
 
-	if (WARN_ON(!obj->relocs))
-		return -EINVAL;
-
-	for (reloc = obj->relocs; reloc->name; reloc++) {
-		if (!klp_is_module(obj)) {
-			ret = klp_verify_vmlinux_symbol(reloc->name,
-							reloc->val);
-			if (ret)
-				return ret;
-		} else {
-			/* module, reloc->val needs to be discovered */
-			if (reloc->external)
-				ret = klp_find_external_symbol(pmod,
-							       reloc->name,
-							       &reloc->val);
-			else
-				ret = klp_find_object_symbol(obj->mod->name,
-							     reloc->name,
-							     &reloc->val);
-			if (ret)
-				return ret;
-		}
-		ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
-					     reloc->val + reloc->addend);
-		if (ret) {
-			pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
-			       reloc->name, reloc->val, ret);
-			return ret;
+	info = pmod->info;
+	symsect = info->sechdrs + info->index.sym;
+	symtab = (void *)info->hdr + symsect->sh_offset;
+
+	/* For each __klp_rela section for this object */
+	list_for_each_entry(reloc_sec, &obj->reloc_secs, list) {
+		relindex = reloc_sec->index;
+		num_relas = info->sechdrs[relindex].sh_size / sizeof(Elf_Rela);
+		rela = (Elf_Rela *) info->sechdrs[relindex].sh_addr;
+
+		/* For each rela in this __klp_rela section */
+		for (i = 0; i < num_relas; i++, rela++) {
+			sym = symtab + ELF_R_SYM(rela->r_info);
+			symname = info->strtab + sym->st_name;
+			bind = ELF_ST_BIND(sym->st_info);
+
+			if (sym->st_shndx == SHN_LIVEPATCH) {
+				if (bind == STB_LIVEPATCH_EXT)
+					ret = klp_find_external_symbol(pmod, symname, &addr);
+				else
+					ret = klp_find_object_symbol(obj->name, symname, &addr);
+				if (ret)
+					return ret;
+				sym->st_value = addr;
+			}
 		}
+		ret = apply_relocate_add(info->sechdrs, info->strtab,
+					 info->index.sym, relindex, pmod);
 	}
 
-	return 0;
+	return ret;
 }
 
 static void notrace klp_ftrace_handler(unsigned long ip,
@@ -741,12 +751,23 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 				  struct klp_object *obj)
 {
 	struct klp_func *func;
+	struct module *pmod;
 	int ret;
 
-	if (obj->relocs) {
-		ret = klp_write_object_relocations(patch->mod, obj);
+	pmod = patch->mod;
+
+	if (!list_empty(&obj->reloc_secs)) {
+		set_page_attributes(pmod->module_core,
+				    pmod->module_core + pmod->core_text_size,
+				    set_memory_rw);
+
+		ret = klp_write_object_relocations(pmod, obj, patch);
 		if (ret)
 			return ret;
+
+		set_page_attributes(pmod->module_core,
+				    pmod->module_core + pmod->core_text_size,
+				    set_memory_ro);
 	}
 
 	klp_for_each_func(obj, func) {
-- 
2.4.3

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