Date:	Mon, 30 Nov 2015 23:21:17 -0500
From:	Jessica Yu <jeyu@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Miroslav Benes <mbenes@...e.cz>
Cc:	linux-api@...r.kernel.org, live-patching@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-doc@...r.kernel.org
Subject: [RFC PATCH v2 4/6] livepatch: reuse module loader code to write relocations

Reuse module loader code to write relocations, thereby eliminating the need
for architecture specific relocation code in livepatch. Namely, we reuse
apply_relocate_add() in the module loader to write relocations 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.

In addition, remove x86 livepatch relocation code. It is no longer needed
since symbol resolution and relocation work have been offloaded to module
loader.   

Signed-off-by: Jessica Yu <jeyu@...hat.com>
---
 arch/x86/include/asm/livepatch.h |  2 -
 arch/x86/kernel/Makefile         |  1 -
 arch/x86/kernel/livepatch.c      | 91 --------------------------------------
 include/linux/livepatch.h        | 30 ++++++-------
 include/linux/module.h           |  6 +++
 kernel/livepatch/core.c          | 94 ++++++++++++++++++++++------------------
 6 files changed, 70 insertions(+), 154 deletions(-)
 delete mode 100644 arch/x86/kernel/livepatch.c

diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
index 19c099a..7312e25 100644
--- a/arch/x86/include/asm/livepatch.h
+++ b/arch/x86/include/asm/livepatch.h
@@ -33,8 +33,6 @@ static inline int klp_check_compiler_support(void)
 #endif
 	return 0;
 }
-int klp_write_module_reloc(struct module *mod, unsigned long type,
-			   unsigned long loc, unsigned long value);
 
 static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
 {
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index b1b78ff..c5e9a5c 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -67,7 +67,6 @@ obj-$(CONFIG_X86_MPPARSE)	+= mpparse.o
 obj-y				+= apic/
 obj-$(CONFIG_X86_REBOOTFIXUPS)	+= reboot_fixups_32.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o
-obj-$(CONFIG_LIVEPATCH)		+= livepatch.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
 obj-$(CONFIG_X86_TSC)		+= trace_clock.o
diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
deleted file mode 100644
index d1d35cc..0000000
--- a/arch/x86/kernel/livepatch.c
+++ /dev/null
@@ -1,91 +0,0 @@
-/*
- * livepatch.c - x86-specific Kernel Live Patching Core
- *
- * Copyright (C) 2014 Seth Jennings <sjenning@...hat.com>
- * Copyright (C) 2014 SUSE
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version 2
- * of the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, see <http://www.gnu.org/licenses/>.
- */
-
-#include <linux/module.h>
-#include <linux/uaccess.h>
-#include <asm/cacheflush.h>
-#include <asm/page_types.h>
-#include <asm/elf.h>
-#include <asm/livepatch.h>
-
-/**
- * klp_write_module_reloc() - write a relocation in a module
- * @mod:	module in which the section to be modified is found
- * @type:	ELF relocation type (see asm/elf.h)
- * @loc:	address that the relocation should be written to
- * @value:	relocation value (sym address + addend)
- *
- * This function writes a relocation to the specified location for
- * a particular module.
- */
-int klp_write_module_reloc(struct module *mod, unsigned long type,
-			   unsigned long loc, unsigned long value)
-{
-	int ret, numpages, size = 4;
-	bool readonly;
-	unsigned long val;
-	unsigned long core = (unsigned long)mod->module_core;
-	unsigned long core_size = mod->core_size;
-
-	switch (type) {
-	case R_X86_64_NONE:
-		return 0;
-	case R_X86_64_64:
-		val = value;
-		size = 8;
-		break;
-	case R_X86_64_32:
-		val = (u32)value;
-		break;
-	case R_X86_64_32S:
-		val = (s32)value;
-		break;
-	case R_X86_64_PC32:
-		val = (u32)(value - loc);
-		break;
-	default:
-		/* unsupported relocation type */
-		return -EINVAL;
-	}
-
-	if (loc < core || loc >= core + core_size)
-		/* loc does not point to any symbol inside the module */
-		return -EINVAL;
-
-	readonly = false;
-
-#ifdef CONFIG_DEBUG_SET_MODULE_RONX
-	if (loc < core + mod->core_ro_size)
-		readonly = true;
-#endif
-
-	/* determine if the relocation spans a page boundary */
-	numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
-
-	if (readonly)
-		set_memory_rw(loc & PAGE_MASK, numpages);
-
-	ret = probe_kernel_write((void *)loc, &val, size);
-
-	if (readonly)
-		set_memory_ro(loc & PAGE_MASK, numpages);
-
-	return ret;
-}
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 31db7a0..54f62a6 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -64,28 +64,21 @@ struct klp_func {
 };
 
 /**
- * struct klp_reloc - relocation structure for live patching
- * @loc:	address where the relocation will be written
- * @val:	address of the referenced symbol (optional,
- *		vmlinux	patches only)
- * @type:	ELF relocation type
- * @name:	name of the referenced symbol (for lookup/verification)
- * @addend:	offset from the referenced symbol
- * @external:	symbol is either exported or within the live patch module itself
+ * struct klp_reloc_sec - relocation section struct for live patching
+ * @index:	Elf section index of the relocation section
+ * @name:	name of the relocation section
+ * @objname:	name of the object associated with the klp reloc section
  */
-struct klp_reloc {
-	unsigned long loc;
-	unsigned long val;
-	unsigned long type;
-	const char *name;
-	int addend;
-	int external;
+struct klp_reloc_sec {
+	unsigned int index;
+	char *name;
+	char *objname;
 };
 
 /**
  * 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 +88,7 @@ struct klp_reloc {
 struct klp_object {
 	/* external */
 	const char *name;
-	struct klp_reloc *relocs;
+	struct klp_reloc_sec *reloc_secs;
 	struct klp_func *funcs;
 
 	/* internal */
@@ -129,6 +122,9 @@ struct klp_patch {
 #define klp_for_each_func(obj, func) \
 	for (func = obj->funcs; func->old_name; func++)
 
+#define klp_for_each_reloc_sec(obj, reloc_sec) \
+	for (reloc_sec = obj->reloc_secs; reloc_sec->name; reloc_sec++)
+
 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 9b46256..ea61147 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -777,9 +777,15 @@ 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 db545cb..17b7278 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -28,6 +28,9 @@
 #include <linux/list.h>
 #include <linux/kallsyms.h>
 #include <linux/livepatch.h>
+#include <linux/elf.h>
+#include <asm/cacheflush.h>
+#include <linux/moduleloader.h>
 
 /**
  * struct klp_ops - structure for tracking registered ftrace ops structs
@@ -281,52 +284,48 @@ 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;
+	char *symname;
+	struct klp_reloc_sec *reloc_sec;
+	Elf_Rela *rela;
+	Elf_Sym *sym, *symtab;
 
 	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)) {
-
-#if defined(CONFIG_RANDOMIZE_BASE)
-			/* If KASLR has been enabled, adjust old value accordingly */
-			if (kaslr_enabled())
-				reloc->val += kaslr_offset();
-#endif
-			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;
+	symtab = (void *)pmod->core_symtab;
+
+	/* For each __klp_rela section for this object */
+	klp_for_each_reloc_sec(obj, reloc_sec) {
+		relindex = reloc_sec->index;
+		num_relas = pmod->sechdrs[relindex].sh_size / sizeof(Elf_Rela);
+		rela = (Elf_Rela *) pmod->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 = pmod->core_strtab + sym->st_name;
+
+			if (sym->st_shndx == SHN_LIVEPATCH) {
+				if (sym->st_info == 'K')
+					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(pmod->sechdrs, pmod->core_strtab,
+					 pmod->index.sym, relindex, pmod);
 	}
 
-	return 0;
+	return ret;
 }
 
 static void notrace klp_ftrace_handler(unsigned long ip,
@@ -747,13 +746,22 @@ 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);
-		if (ret)
-			return ret;
-	}
+	pmod = patch->mod;
+
+	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) {
 		ret = klp_find_verify_func_addr(obj, func);
-- 
2.4.3

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