[PATCH v3] RO/NX protection for loadable kernel modules
From: Siarhei Liakh
Date: Sun Jul 05 2009 - 19:24:22 EST
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,
module_free() have been modified to set module_core or module_init as
RW+NX right before calling vfree().
By default, the original section layout is preserved and RO/NX is
enforced only for whole pages of same content.
However, when compiled with CONFIG_DEBUG_RODATA=y, the patch
will page-align each group of section to ensure that each page contains
only one type of content mentioned above.
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 have been corrected also.
v3: Opportunistic RO/NX protectiuon is now unconditional. Section
page-alignment is enabled when CONFIG_DEBUG_RODATA=y.
The patch have been developed for Linux 2.6.30 by Siarhei Liakh
<sliakh.lkml@xxxxxxxxx> and Xuxian Jiang <jiang@xxxxxxxxxxx>.
---
Signed-off-by: Siarhei Liakh <sliakh.lkml@xxxxxxxxx>
Signed-off-by: Xuxian Jiang <jiang@xxxxxxxxxxx>
diff --git a/include/linux/module.h b/include/linux/module.h
index 627ac08..5ba770e 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -293,6 +293,9 @@ 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;
diff --git a/kernel/module.c b/kernel/module.c
index e797812..357ab77 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -63,6 +63,45 @@
#define ARCH_SHF_SMALL 0
#endif
+/* Modules' sections will be aligned on page boundaries
+ * to ensure complete separation of code and data */
+#ifdef CONFIG_DEBUG_RODATA
+#define ALIGN_MODULE_SECTION(SECTION, ALIGNMENT) \
+ do { SECTION = ALIGN(SECTION, ALIGNMENT); } while (0)
+#else
+#define ALIGN_MODULE_SECTION(SECTION, ALIGNMENT) do { ; } while (0)
+#endif
+
+/* Given a virtual address returns 1 if the address is page-aligned,
+ * 0 otherwise */
+#define PAGE_ALIGNED(ADDR) (((unsigned long) ADDR & \
+ ((1UL << PAGE_SHIFT) - 1UL)) ? \
+ (0) : (1))
+
+/* Given a virtual address returns a virtual page number
+ * that contains that address */
+#define PAGE_NUMBER(ADDR) (((unsigned long) ADDR) >> PAGE_SHIFT)
+
+/* Given BASE and SIZE this macro calculates the number of pages the
+ * memory regions occupies */
+#define NUMBER_OF_PAGES(BASE, SIZE) ((SIZE > 0) ? \
+ (PAGE_NUMBER(BASE + SIZE - 1) - \
+ PAGE_NUMBER(BASE) + 1) \
+ : (0UL))
+
+/* This macro catches a section group with SEC_ID and records it's
+ * size into SEC_SIZE, aligning it (as well as SIZE) on page boundary
+ * if necessary */
+#define CATCH_MODULE_SECTION(SEC_GROUP, SEC_ID, SEC_SIZE, SIZE) \
+ do { \
+ if (SEC_GROUP == SEC_ID) { \
+ /* align section size to a page */ \
+ ALIGN_MODULE_SECTION(SIZE, PAGE_SIZE); \
+ /* set new module section size */ \
+ SEC_SIZE = SIZE; \
+ } \
+ } while (0)
+
/* If this is set, the section belongs in the init part of the module */
#define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))
@@ -187,6 +226,35 @@ extern const unsigned long __start___kcrctab_unused_gpl[];
#define symversion(base, idx) ((base != NULL) ? ((base) + (idx)) : NULL)
#endif
+/* Generic memory allocation for modules, since
+ * module_alloc() is platform-specific */
+#define generic_module_alloc(size) module_alloc(size)
+
+/* Free memory returned from generic_module_alloc, since
+ * module_free() is platform-specific */
+void generic_module_free(struct module *mod, void *module_region)
+{
+ unsigned long total_pages;
+
+ if (mod->module_core == module_region) {
+ /* Set core as NX+RW */
+ total_pages = NUMBER_OF_PAGES(mod->module_core, mod->core_size);
+ DEBUGP("RELEASING MODULE CORE: 0x%lx %lu\n",
+ (unsigned long)mod->module_core, total_pages);
+ 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 = NUMBER_OF_PAGES(mod->module_init, mod->init_size);
+ DEBUGP("RELEASING MODULE INIT: 0x%lx %lu\n",
+ (unsigned long)mod->module_init, total_pages);
+ set_memory_nx((unsigned long)mod->module_init, total_pages);
+ set_memory_rw((unsigned long)mod->module_init, total_pages);
+ }
+ module_free(mod, module_region);
+}
+
static bool each_symbol_in_section(const struct symsearch *arr,
unsigned int arrsize,
struct module *owner,
@@ -1493,7 +1561,7 @@ static void free_module(struct module *mod)
ftrace_release(mod->module_core, mod->core_size);
/* This may be NULL, but that's OK */
- module_free(mod, mod->module_init);
+ generic_module_free(mod, mod->module_init);
kfree(mod->args);
if (mod->percpu)
percpu_modfree(mod->percpu);
@@ -1505,7 +1573,7 @@ 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) */
- module_free(mod, mod->module_core);
+ generic_module_free(mod, mod->module_core);
}
void *__symbol_get(const char *symbol)
@@ -1678,8 +1746,18 @@ static void layout_sections(struct module *mod,
s->sh_entsize = get_offset(mod, &mod->core_size, s, i);
DEBUGP("\t%s\n", secstrings + s->sh_name);
}
- if (m == 0)
- mod->core_text_size = mod->core_size;
+ /* SECTION 0: executable code (text)*/
+ CATCH_MODULE_SECTION(m, 0, mod->core_text_size,
+ mod->core_size);
+
+ /* SECTION 1: RO data (executable code + RO data)*/
+ CATCH_MODULE_SECTION(m, 1, mod->core_ro_size,
+ mod->core_size);
+
+ /* SECTION 3: whole module (executable code + RO data +
+ * RW data + small alloc )*/
+ CATCH_MODULE_SECTION(m, 3, mod->core_size,
+ mod->core_size);
}
DEBUGP("Init section allocation order:\n");
@@ -1696,8 +1774,18 @@ static void layout_sections(struct module *mod,
| INIT_OFFSET_MASK);
DEBUGP("\t%s\n", secstrings + s->sh_name);
}
- if (m == 0)
- mod->init_text_size = mod->init_size;
+ /* SECTION 0: executable code (text)*/
+ CATCH_MODULE_SECTION(m, 0, mod->init_text_size,
+ mod->init_size);
+
+ /* SECTION 1: RO data (executable code + RO data)*/
+ CATCH_MODULE_SECTION(m, 1, mod->init_ro_size,
+ mod->init_size);
+
+ /* SECTION 3: whole module (executable code + RO data +
+ * RW data + small alloc )*/
+ CATCH_MODULE_SECTION(m, 3, mod->init_size,
+ mod->init_size);
}
}
@@ -1866,7 +1954,7 @@ static void dynamic_debug_setup(struct _ddebug
*debug, unsigned int num)
static void *module_alloc_update_bounds(unsigned long size)
{
- void *ret = module_alloc(size);
+ void *ret = generic_module_alloc(size);
if (ret) {
/* Update module bounds. */
@@ -1878,6 +1966,72 @@ static void
*module_alloc_update_bounds(unsigned long size)
return ret;
}
+/* LKM RO/NX protection: protect module's text/ro-data
+ * from modification and any data from execution.
+ * Siarhei Liakh, Xuxian Jiang */
+static void set_section_ro_nx(unsigned long base,
+ unsigned long text_size,
+ unsigned long ro_size,
+ unsigned long total_size)
+{
+ /* begin and end addresses of the current subsection */
+ unsigned long begin_addr;
+ unsigned long end_addr;
+ unsigned long pg_count; /*number of pages that will be affectred*/
+
+ /* Initially, all module sections have RWX permissions*/
+
+ DEBUGP("PROTECTING MODULE SECTION: 0x%lx\n"
+ " text size: %lu\n"
+ " ro size: %lu\n"
+ " total size: %lu\n",
+ base, text_size, ro_size, total_size);
+
+ /* Set RO for module text and RO-data*/
+ if (ro_size > 0) {
+ begin_addr = base;
+ end_addr = begin_addr + ro_size;
+
+ /*skip last page if end address is not page-aligned*/
+ if (!PAGE_ALIGNED(end_addr))
+ end_addr = ALIGN(end_addr - PAGE_SIZE, PAGE_SIZE);
+
+ /*Set text RO if there are still pages between begin and end*/
+ if (end_addr > begin_addr) {
+ pg_count = PAGE_NUMBER(end_addr - 1) -
+ PAGE_NUMBER(begin_addr) + 1;
+ DEBUGP(" RO: 0x%lx %lu\n", begin_addr, pg_count);
+ set_memory_ro(begin_addr, pg_count);
+ } else {
+ DEBUGP(" RO: less than a page, not enforcing.\n");
+ }
+ } else {
+ DEBUGP(" RO: section not present.\n");
+ }
+
+ /* Set NX permissions for module data */
+ if (total_size > text_size) {
+ begin_addr = base + text_size;
+ end_addr = base + total_size;
+
+ /*skip first page if beginning address is not page-aligned*/
+ if (!PAGE_ALIGNED(begin_addr))
+ begin_addr = ALIGN(begin_addr, PAGE_SIZE);
+
+ /*Set data NX if there are still pages between begin and end*/
+ if (end_addr > begin_addr) {
+ pg_count = PAGE_NUMBER(end_addr - 1) -
+ PAGE_NUMBER(begin_addr) + 1;
+ DEBUGP(" NX: 0x%lx %lu\n", begin_addr, pg_count);
+ set_memory_nx(begin_addr, pg_count);
+ } else {
+ DEBUGP(" NX: less than a page, not enforcing.\n");
+ }
+ } else {
+ DEBUGP(" NX: section not present.\n");
+ }
+}
+
/* Allocate and load the module: note that size of section 0 is always
zero, and we rely on this for optional sections. */
static noinline struct module *load_module(void __user *umod,
@@ -2291,6 +2445,18 @@ static noinline struct module *load_module(void
__user *umod,
/* Get rid of temporary copy */
vfree(hdr);
+ /* Set RO and NX regions for core */
+ set_section_ro_nx((unsigned long)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((unsigned long)mod->module_init,
+ mod->init_text_size,
+ mod->init_ro_size,
+ mod->init_size);
+
/* Done! */
return mod;
@@ -2309,9 +2475,9 @@ static noinline struct module *load_module(void
__user *umod,
free_init:
percpu_modfree(mod->refptr);
#endif
- module_free(mod, mod->module_init);
+ generic_module_free(mod, mod->module_init);
free_core:
- module_free(mod, mod->module_core);
+ generic_module_free(mod, mod->module_core);
/* mod will be freed with core. Don't access it beyond this line! */
free_percpu:
if (percpu)
@@ -2394,7 +2560,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
mutex_lock(&module_mutex);
/* Drop initial reference. */
module_put(mod);
- module_free(mod, mod->module_init);
+ generic_module_free(mod, mod->module_init);
mod->module_init = NULL;
mod->init_size = 0;
mod->init_text_size = 0;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/