Message-ID: <AANLkTilNOMfaNrR7sKiGnFq8DEaHy7hLyTofFuLz6zxb@mail.gmail.com>
Date:	Thu, 27 May 2010 12:55:06 -0400
From:	Siarhei Liakh <sliakh.lkml@...il.com>
To:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-next@...r.kernel.org
Cc:	Arjan van de Ven <arjan@...radead.org>,
	James Morris <jmorris@...ei.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@....de>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Dave Jones <davej@...hat.com>
Subject: [PATCH 4/4] [tip:x86/mm] 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 have been corrected also.
V3: Opportunistic RO/NX protectiuon 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 adjutments for -tip

Signed-off-by: Siarhei Liakh <sliakh.lkml@...il.com>
Signed-off-by: Xuxian Jiang <jiang@...ncsu.edu>
Acked-by: Arjan van de Ven <arjan@...ux.intel.com>
Reviewed-by: James Morris <jmorris@...ei.org>
Signed-off-by: H. Peter Anvin <hpa@...or.com>
---

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;

@@ -2508,6 +2685,7 @@ 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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