Patchwork [4/4,tip:x86/mm] RO/NX protection for loadable kernel modules

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Submitter Siarhei Liakh
Date April 1, 2010, 1:59 a.m.
Message ID <g2g817ecb6f1003311859k505d752pb6f2a5d7a31e392@mail.gmail.com>
Download mbox | patch
Permalink /patch/90047/
State New, archived
Headers show

Comments

Patch

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 4814d35..2b1d2bd 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -115,6 +115,17 @@  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"
+	default n
+	depends on X86 && MODULES
+	---help---
+	  This option helps to catch unintended modifications to loadable
+	  kernel module's text and read-only data. It also prevents execution
+	  of LKM's data. Such protection may interfere with run-time code
+	  patching and dynamic kernel tracing.
+	  If in doubt, say "N".
+
 config DEBUG_NX_TEST
 	tristate "Testcase for the NX non-executable stack feature"
 	depends on DEBUG_KERNEL && m
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index cd37469..fa9f170 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -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;
 }
diff --git a/include/linux/module.h b/include/linux/module.h
index 5e869ff..239a34c 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -301,6 +301,9 @@  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;

@@ -534,6 +537,9 @@  extern void print_modules(void);
 extern void module_update_tracepoints(void);
 extern int module_get_iter_tracepoints(struct tracepoint_iter *iter);

+void set_all_modules_text_rw(void);
+void set_all_modules_text_ro(void);
+
 #else /* !CONFIG_MODULES... */
 #define EXPORT_SYMBOL(sym)
 #define EXPORT_SYMBOL_GPL(sym)
@@ -654,6 +660,13 @@  static inline int
module_get_iter_tracepoints(struct tracepoint_iter *iter)
 	return 0;
 }

+static inline void set_all_modules_text_rw(void)
+{
+}
+
+static inline void set_all_modules_text_ro(void)
+{
+}
 #endif /* CONFIG_MODULES */

 struct device_driver;
diff --git a/kernel/module.c b/kernel/module.c
index c968d36..2020c6d 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -55,6 +55,7 @@ 
 #include <linux/async.h>
 #include <linux/percpu.h>
 #include <linux/kmemleak.h>
+#include <linux/pfn.h>

 #define CREATE_TRACE_POINTS
 #include <trace/events/module.h>
@@ -71,6 +72,26 @@  EXPORT_TRACEPOINT_SYMBOL(module_get);
 #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 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))

@@ -1377,6 +1398,126 @@  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 = 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 = 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 void set_section_ro_nx(void *base,
+			unsigned long text_size,
+			unsigned long ro_size,
+			unsigned long total_size) { }
+
+void unset_section_ro_nx(struct module *mod, void *module_region) { }
+void set_all_modules_text_rw() { }
+void set_all_modules_text_ro() { }
+#endif
+
 /* Free a module, remove from lists, etc (must hold module_mutex). */
 static void free_module(struct module *mod)
 {
@@ -1398,6 +1539,7 @@  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);
 	if (mod->percpu)
@@ -1410,6 +1552,7 @@  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
@@ -1587,8 +1730,19 @@  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)
+		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");
@@ -1605,8 +1759,19 @@  static void layout_sections(struct module *mod,
 					 | INIT_OFFSET_MASK);
 			DEBUGP("\t%s\n", secstrings + s->sh_name);
 		}
-		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;
+		}
 	}
 }

@@ -2386,6 +2551,18 @@  static noinline struct module *load_module(void
__user *umod,

 	trace_module_load(mod);

+	/* 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! */
 	return mod;