Commit 425595a7 authored by Jessica Yu's avatar Jessica Yu Committed by Jiri Kosina

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. Specifically, reuse
the apply_relocate_add() function in the module loader to write relocations
instead of duplicating functionality in livepatch's arch-dependent
klp_write_module_reloc() function.

In order to accomplish this, livepatch modules manage their own relocation
sections (marked with the SHF_RELA_LIVEPATCH section flag) and
livepatch-specific symbols (marked with SHN_LIVEPATCH symbol section
index). To apply livepatch relocation sections, 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 and the s390
klp_write_module_reloc() function stub. They are no longer needed since
relocation work has been offloaded to module loader.

Lastly, mark the module as a livepatch module so that the module loader
canappropriately identify and initialize it.
Signed-off-by: 's avatarJessica Yu <jeyu@redhat.com>
Reviewed-by: 's avatarMiroslav Benes <mbenes@suse.cz>
Acked-by: 's avatarJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>   # for s390 changes
Signed-off-by: 's avatarJiri Kosina <jkosina@suse.cz>
parent f31e0960
......@@ -24,13 +24,6 @@ static inline int klp_check_compiler_support(void)
return 0;
}
static inline int klp_write_module_reloc(struct module *mod, unsigned long
type, unsigned long loc, unsigned long value)
{
/* not supported yet */
return -ENOSYS;
}
static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
{
regs->psw.addr = ip;
......
......@@ -32,8 +32,6 @@ 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)
{
......
......@@ -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
......
/*
* livepatch.c - x86-specific Kernel Live Patching Core
*
* Copyright (C) 2014 Seth Jennings <sjenning@redhat.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/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)
{
size_t size = 4;
unsigned long val;
unsigned long core = (unsigned long)mod->core_layout.base;
unsigned long core_size = mod->core_layout.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;
return probe_kernel_write((void *)loc, &val, size);
}
......@@ -64,28 +64,9 @@ struct klp_func {
struct list_head stack_node;
};
/**
* struct klp_reloc - relocation structure for live patching
* @loc: address where the relocation will be written
* @sympos: position in kallsyms to disambiguate symbols (optional)
* @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 {
unsigned long loc;
unsigned long sympos;
unsigned long type;
const char *name;
int addend;
int external;
};
/**
* 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
* @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 +76,6 @@ struct klp_reloc {
struct klp_object {
/* external */
const char *name;
struct klp_reloc *relocs;
struct klp_func *funcs;
/* internal */
......
......@@ -28,6 +28,8 @@
#include <linux/list.h>
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
#include <linux/elf.h>
#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
/**
......@@ -204,75 +206,109 @@ static int klp_find_object_symbol(const char *objname, const char *name,
return -EINVAL;
}
/*
* external symbols are located outside the parent object (where the parent
* object is either vmlinux or the kmod being patched).
*/
static int klp_find_external_symbol(struct module *pmod, const char *name,
unsigned long *addr)
static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
{
const struct kernel_symbol *sym;
/* first, check if it's an exported symbol */
preempt_disable();
sym = find_symbol(name, NULL, NULL, true, true);
if (sym) {
*addr = sym->value;
preempt_enable();
return 0;
}
preempt_enable();
int i, cnt, vmlinux, ret;
char objname[MODULE_NAME_LEN];
char symname[KSYM_NAME_LEN];
char *strtab = pmod->core_kallsyms.strtab;
Elf_Rela *relas;
Elf_Sym *sym;
unsigned long sympos, addr;
/*
* Check if it's in another .o within the patch module. This also
* checks that the external symbol is unique.
* Since the field widths for objname and symname in the sscanf()
* call are hard-coded and correspond to MODULE_NAME_LEN and
* KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
* and KSYM_NAME_LEN have the values we expect them to have.
*
* Because the value of MODULE_NAME_LEN can differ among architectures,
* we use the smallest/strictest upper bound possible (56, based on
* the current definition of MODULE_NAME_LEN) to prevent overflows.
*/
return klp_find_object_symbol(pmod->name, name, 0, addr);
BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
relas = (Elf_Rela *) relasec->sh_addr;
/* For each rela in this klp relocation section */
for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
if (sym->st_shndx != SHN_LIVEPATCH) {
pr_err("symbol %s is not marked as a livepatch symbol",
strtab + sym->st_name);
return -EINVAL;
}
/* Format: .klp.sym.objname.symname,sympos */
cnt = sscanf(strtab + sym->st_name,
".klp.sym.%55[^.].%127[^,],%lu",
objname, symname, &sympos);
if (cnt != 3) {
pr_err("symbol %s has an incorrectly formatted name",
strtab + sym->st_name);
return -EINVAL;
}
/* klp_find_object_symbol() treats a NULL objname as vmlinux */
vmlinux = !strcmp(objname, "vmlinux");
ret = klp_find_object_symbol(vmlinux ? NULL : objname,
symname, sympos, &addr);
if (ret)
return ret;
sym->st_value = addr;
}
return 0;
}
static int klp_write_object_relocations(struct module *pmod,
struct klp_object *obj)
{
int ret = 0;
unsigned long val;
struct klp_reloc *reloc;
int i, cnt, ret = 0;
const char *objname, *secname;
char sec_objname[MODULE_NAME_LEN];
Elf_Shdr *sec;
if (WARN_ON(!klp_is_object_loaded(obj)))
return -EINVAL;
if (WARN_ON(!obj->relocs))
return -EINVAL;
objname = klp_is_module(obj) ? obj->name : "vmlinux";
module_disable_ro(pmod);
/* For each klp relocation section */
for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
sec = pmod->klp_info->sechdrs + i;
secname = pmod->klp_info->secstrings + sec->sh_name;
if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
continue;
for (reloc = obj->relocs; reloc->name; reloc++) {
/* discover the address of the referenced symbol */
if (reloc->external) {
if (reloc->sympos > 0) {
pr_err("non-zero sympos for external reloc symbol '%s' is not supported\n",
reloc->name);
ret = -EINVAL;
goto out;
}
ret = klp_find_external_symbol(pmod, reloc->name, &val);
} else
ret = klp_find_object_symbol(obj->name,
reloc->name,
reloc->sympos,
&val);
/*
* Format: .klp.rela.sec_objname.section_name
* See comment in klp_resolve_symbols() for an explanation
* of the selected field width value.
*/
cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
if (cnt != 1) {
pr_err("section %s has an incorrectly formatted name",
secname);
ret = -EINVAL;
break;
}
if (strcmp(objname, sec_objname))
continue;
ret = klp_resolve_symbols(sec, pmod);
if (ret)
goto out;
break;
ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
val + reloc->addend);
if (ret) {
pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
reloc->name, val, ret);
goto out;
}
ret = apply_relocate_add(pmod->klp_info->sechdrs,
pmod->core_kallsyms.strtab,
pmod->klp_info->symndx, i, pmod);
if (ret)
break;
}
out:
module_enable_ro(pmod);
return ret;
}
......@@ -703,11 +739,9 @@ static int klp_init_object_loaded(struct klp_patch *patch,
struct klp_func *func;
int ret;
if (obj->relocs) {
ret = klp_write_object_relocations(patch->mod, obj);
if (ret)
return ret;
}
ret = klp_write_object_relocations(patch->mod, obj);
if (ret)
return ret;
klp_for_each_func(obj, func) {
ret = klp_find_object_symbol(obj->name, func->old_name,
......@@ -842,6 +876,12 @@ int klp_register_patch(struct klp_patch *patch)
{
int ret;
if (!is_livepatch_module(patch->mod)) {
pr_err("module %s is not marked as a livepatch module",
patch->mod->name);
return -EINVAL;
}
if (!klp_initialized())
return -ENODEV;
......
......@@ -89,3 +89,4 @@ static void livepatch_exit(void)
module_init(livepatch_init);
module_exit(livepatch_exit);
MODULE_LICENSE("GPL");
MODULE_INFO(livepatch, "Y");
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment