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: Siarhei Liakh <sliakh.lkml@gmail.com>
Signed-off-by: Xuxian Jiang <jiang@cs.ncsu.edu>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Reviewed-by: James Morris <jmorris@namei.org>
Signed-off-by: H. 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: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/module.c b/kernel/module.c
index 437a74a..ba421e6 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -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 @@
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 @@
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 @@
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 @@
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 @@
| 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 @@
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 @@
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;
