Commit 84e1c6bb authored by matthieu castet's avatar matthieu castet Committed by Ingo Molnar

x86: Add RO/NX protection for loadable kernel modules

This patch is a logical extension of the protection provided by
CONFIG_DEBUG_RODATA to LKMs. The protection is provided by
splitting module_core and module_init into three logical parts
each and setting appropriate page access permissions for each
individual section:

 1. Code: RO+X
 2. RO data: RO+NX
 3. RW data: RW+NX

In order to achieve proper protection, layout_sections() have
been modified to align each of the three parts mentioned above
onto page boundary. Next, the corresponding page access
permissions are set right before successful exit from
load_module(). Further, free_module() and sys_init_module have
been modified to set module_core and module_init as RW+NX right
before calling module_free().

By default, the original section layout and access flags are
preserved. When compiled with CONFIG_DEBUG_SET_MODULE_RONX=y,
the patch will page-align each group of sections to ensure that
each page contains only one type of content and will enforce
RO/NX for each group of pages.

  -v1: Initial proof-of-concept patch.
  -v2: The patch have been re-written to reduce the number of #ifdefs
       and to make it architecture-agnostic. Code formatting has also
       been corrected.
  -v3: Opportunistic RO/NX protection is now unconditional. Section
       page-alignment is enabled when CONFIG_DEBUG_RODATA=y.
  -v4: Removed most macros and improved coding style.
  -v5: Changed page-alignment and RO/NX section size calculation
  -v6: Fixed comments. Restricted RO/NX enforcement to x86 only
  -v7: Introduced CONFIG_DEBUG_SET_MODULE_RONX, added
       calls to set_all_modules_text_rw() and set_all_modules_text_ro()
       in ftrace
  -v8: updated for compatibility with linux 2.6.33-rc5
  -v9: coding style fixes
 -v10: more coding style fixes
 -v11: minor adjustments for -tip
 -v12: minor adjustments for v2.6.35-rc2-tip
 -v13: minor adjustments for v2.6.37-rc1-tip
Signed-off-by: default avatarSiarhei Liakh <sliakh.lkml@gmail.com>
Signed-off-by: default avatarXuxian Jiang <jiang@cs.ncsu.edu>
Acked-by: default avatarArjan van de Ven <arjan@linux.intel.com>
Reviewed-by: default avatarJames Morris <jmorris@namei.org>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dave Jones <davej@redhat.com>
Cc: Kees Cook <kees.cook@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4CE2F914.9070106@free.fr>
[ minor cleanliness edits, -v14: build failure fix ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 5bd5a452
......@@ -117,6 +117,17 @@ config DEBUG_RODATA_TEST
feature as well as for the change_page_attr() infrastructure.
If in doubt, say "N"
config DEBUG_SET_MODULE_RONX
bool "Set loadable kernel module data as NX and text as RO"
depends on MODULES
---help---
This option helps catch unintended modifications to loadable
kernel module's text and read-only data. It also prevents execution
of module data. Such protection may interfere with run-time code
patching and dynamic kernel tracing - and they might also protect
against certain classes of kernel exploits.
If in doubt, say "N".
config DEBUG_NX_TEST
tristate "Testcase for the NX non-executable stack feature"
depends on DEBUG_KERNEL && m
......
......@@ -19,6 +19,7 @@
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/module.h>
#include <trace/syscall.h>
......@@ -49,6 +50,7 @@ static DEFINE_PER_CPU(int, save_modifying_code);
int ftrace_arch_code_modify_prepare(void)
{
set_kernel_text_rw();
set_all_modules_text_rw();
modifying_code = 1;
return 0;
}
......@@ -56,6 +58,7 @@ int ftrace_arch_code_modify_prepare(void)
int ftrace_arch_code_modify_post_process(void)
{
modifying_code = 0;
set_all_modules_text_ro();
set_kernel_text_ro();
return 0;
}
......
......@@ -308,6 +308,9 @@ struct module
/* The size of the executable code in each section. */
unsigned int init_text_size, core_text_size;
/* Size of RO sections of the module (text+rodata) */
unsigned int init_ro_size, core_ro_size;
/* Arch-specific module values */
struct mod_arch_specific arch;
......@@ -672,7 +675,6 @@ static inline int module_get_iter_tracepoints(struct tracepoint_iter *iter)
{
return 0;
}
#endif /* CONFIG_MODULES */
#ifdef CONFIG_SYSFS
......@@ -687,6 +689,13 @@ extern int module_sysfs_initialized;
#define __MODULE_STRING(x) __stringify(x)
#ifdef CONFIG_DEBUG_SET_MODULE_RONX
extern void set_all_modules_text_rw(void);
extern void set_all_modules_text_ro(void);
#else
static inline void set_all_modules_text_rw(void) { }
static inline void set_all_modules_text_ro(void) { }
#endif
#ifdef CONFIG_GENERIC_BUG
void module_bug_finalize(const Elf_Ehdr *, const Elf_Shdr *,
......
......@@ -56,6 +56,7 @@
#include <linux/percpu.h>
#include <linux/kmemleak.h>
#include <linux/jump_label.h>
#include <linux/pfn.h>
#define CREATE_TRACE_POINTS
#include <trace/events/module.h>
......@@ -70,6 +71,26 @@
#define ARCH_SHF_SMALL 0
#endif
/*
* Modules' sections will be aligned on page boundaries
* to ensure complete separation of code and data, but
* only when CONFIG_DEBUG_SET_MODULE_RONX=y
*/
#ifdef CONFIG_DEBUG_SET_MODULE_RONX
# define debug_align(X) ALIGN(X, PAGE_SIZE)
#else
# define debug_align(X) (X)
#endif
/*
* Given BASE and SIZE this macro calculates the number of pages the
* memory regions occupies
*/
#define MOD_NUMBER_OF_PAGES(BASE, SIZE) (((SIZE) > 0) ? \
(PFN_DOWN((unsigned long)(BASE) + (SIZE) - 1) - \
PFN_DOWN((unsigned long)BASE) + 1) \
: (0UL))
/* If this is set, the section belongs in the init part of the module */
#define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))
......@@ -1542,6 +1563,115 @@ static int __unlink_module(void *_mod)
return 0;
}
#ifdef CONFIG_DEBUG_SET_MODULE_RONX
/*
* LKM RO/NX protection: protect module's text/ro-data
* from modification and any data from execution.
*/
void set_page_attributes(void *start, void *end, int (*set)(unsigned long start, int num_pages))
{
unsigned long begin_pfn = PFN_DOWN((unsigned long)start);
unsigned long end_pfn = PFN_DOWN((unsigned long)end);
if (end_pfn > begin_pfn)
set(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn);
}
static void set_section_ro_nx(void *base,
unsigned long text_size,
unsigned long ro_size,
unsigned long total_size)
{
/* begin and end PFNs of the current subsection */
unsigned long begin_pfn;
unsigned long end_pfn;
/*
* Set RO for module text and RO-data:
* - Always protect first page.
* - Do not protect last partial page.
*/
if (ro_size > 0)
set_page_attributes(base, base + ro_size, set_memory_ro);
/*
* Set NX permissions for module data:
* - Do not protect first partial page.
* - Always protect last page.
*/
if (total_size > text_size) {
begin_pfn = PFN_UP((unsigned long)base + text_size);
end_pfn = PFN_UP((unsigned long)base + total_size);
if (end_pfn > begin_pfn)
set_memory_nx(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn);
}
}
/* Setting memory back to RW+NX before releasing it */
void unset_section_ro_nx(struct module *mod, void *module_region)
{
unsigned long total_pages;
if (mod->module_core == module_region) {
/* Set core as NX+RW */
total_pages = MOD_NUMBER_OF_PAGES(mod->module_core, mod->core_size);
set_memory_nx((unsigned long)mod->module_core, total_pages);
set_memory_rw((unsigned long)mod->module_core, total_pages);
} else if (mod->module_init == module_region) {
/* Set init as NX+RW */
total_pages = MOD_NUMBER_OF_PAGES(mod->module_init, mod->init_size);
set_memory_nx((unsigned long)mod->module_init, total_pages);
set_memory_rw((unsigned long)mod->module_init, total_pages);
}
}
/* Iterate through all modules and set each module's text as RW */
void set_all_modules_text_rw()
{
struct module *mod;
mutex_lock(&module_mutex);
list_for_each_entry_rcu(mod, &modules, list) {
if ((mod->module_core) && (mod->core_text_size)) {
set_page_attributes(mod->module_core,
mod->module_core + mod->core_text_size,
set_memory_rw);
}
if ((mod->module_init) && (mod->init_text_size)) {
set_page_attributes(mod->module_init,
mod->module_init + mod->init_text_size,
set_memory_rw);
}
}
mutex_unlock(&module_mutex);
}
/* Iterate through all modules and set each module's text as RO */
void set_all_modules_text_ro()
{
struct module *mod;
mutex_lock(&module_mutex);
list_for_each_entry_rcu(mod, &modules, list) {
if ((mod->module_core) && (mod->core_text_size)) {
set_page_attributes(mod->module_core,
mod->module_core + mod->core_text_size,
set_memory_ro);
}
if ((mod->module_init) && (mod->init_text_size)) {
set_page_attributes(mod->module_init,
mod->module_init + mod->init_text_size,
set_memory_ro);
}
}
mutex_unlock(&module_mutex);
}
#else
static inline void set_section_ro_nx(void *base, unsigned long text_size, unsigned long ro_size, unsigned long total_size) { }
static inline void unset_section_ro_nx(struct module *mod, void *module_region) { }
#endif
/* Free a module, remove from lists, etc. */
static void free_module(struct module *mod)
{
......@@ -1566,6 +1696,7 @@ static void free_module(struct module *mod)
destroy_params(mod->kp, mod->num_kp);
/* This may be NULL, but that's OK */
unset_section_ro_nx(mod, mod->module_init);
module_free(mod, mod->module_init);
kfree(mod->args);
percpu_modfree(mod);
......@@ -1574,6 +1705,7 @@ static void free_module(struct module *mod)
lockdep_free_key_range(mod->module_core, mod->core_size);
/* Finally, free the core (containing the module structure) */
unset_section_ro_nx(mod, mod->module_core);
module_free(mod, mod->module_core);
#ifdef CONFIG_MPU
......@@ -1777,8 +1909,19 @@ static void layout_sections(struct module *mod, struct load_info *info)
s->sh_entsize = get_offset(mod, &mod->core_size, s, i);
DEBUGP("\t%s\n", name);
}
if (m == 0)
switch (m) {
case 0: /* executable */
mod->core_size = debug_align(mod->core_size);
mod->core_text_size = mod->core_size;
break;
case 1: /* RO: text and ro-data */
mod->core_size = debug_align(mod->core_size);
mod->core_ro_size = mod->core_size;
break;
case 3: /* whole core */
mod->core_size = debug_align(mod->core_size);
break;
}
}
DEBUGP("Init section allocation order:\n");
......@@ -1796,8 +1939,19 @@ static void layout_sections(struct module *mod, struct load_info *info)
| INIT_OFFSET_MASK);
DEBUGP("\t%s\n", sname);
}
if (m == 0)
switch (m) {
case 0: /* executable */
mod->init_size = debug_align(mod->init_size);
mod->init_text_size = mod->init_size;
break;
case 1: /* RO: text and ro-data */
mod->init_size = debug_align(mod->init_size);
mod->init_ro_size = mod->init_size;
break;
case 3: /* whole init */
mod->init_size = debug_align(mod->init_size);
break;
}
}
}
......@@ -2650,6 +2804,18 @@ static struct module *load_module(void __user *umod,
kfree(info.strmap);
free_copy(&info);
/* Set RO and NX regions for core */
set_section_ro_nx(mod->module_core,
mod->core_text_size,
mod->core_ro_size,
mod->core_size);
/* Set RO and NX regions for init */
set_section_ro_nx(mod->module_init,
mod->init_text_size,
mod->init_ro_size,
mod->init_size);
/* Done! */
trace_module_load(mod);
return mod;
......@@ -2753,6 +2919,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
mod->symtab = mod->core_symtab;
mod->strtab = mod->core_strtab;
#endif
unset_section_ro_nx(mod, mod->module_init);
module_free(mod, mod->module_init);
mod->module_init = NULL;
mod->init_size = 0;
......
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