[RFC PATCH v2 4/6] livepatch: reuse module loader code to write relocations

From: Jessica Yu
Date: Mon Nov 30 2015 - 23:22:04 EST

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@xxxxxxxxxx>
---
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@xxxxxxxxxx>
- * 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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