Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753497Ab0BAXkA (ORCPT ); Mon, 1 Feb 2010 18:40:00 -0500 Received: from mail-bw0-f223.google.com ([209.85.218.223]:40743 "EHLO mail-bw0-f223.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752107Ab0BAXj4 (ORCPT ); Mon, 1 Feb 2010 18:39:56 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:cc:content-type; b=uGKQ8AjYnkKJVaCF6ExnCb+eqOohC94xXNlP16eRKVQ22z99IG+jUS0Tssc7CnkWVJ f1FgLX+lpJlg/sff37Lxc1TBz51bDSmsOvYPKXigWoopxW4Dc7x7L+QCOlym8DWiBLBm Cs0dyIWZinURONU8ZJl1neSLVepQDvRDbxmG8= MIME-Version: 1.0 Date: Mon, 1 Feb 2010 18:39:53 -0500 Message-ID: <817ecb6f1002011539g3f30416fi60c7c5222cab8f3@mail.gmail.com> Subject: [PATCH V10] RO/NX protection for loadable kernel modules From: Siarhei Liakh To: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-next@vger.kernel.org Cc: Arjan van de Ven , James Morris , Andrew Morton , Andi Kleen , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , Rusty Russell , Stephen Rothwell , Dave Jones Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 12034 Lines: 394 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 The patch have been developed for Linux 2.6.33-rc5 by Siarhei Liakh and Xuxian Jiang . --- Signed-off-by: Siarhei Liakh Signed-off-by: Xuxian Jiang Acked-by: Arjan van de Ven Reviewed-by: James Morris diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index bc01e3e..7c80e28 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 3096892..b47a154 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -19,6 +19,7 @@ #include #include #include +#include #include @@ -29,16 +30,17 @@ #ifdef CONFIG_DYNAMIC_FTRACE - int ftrace_arch_code_modify_prepare(void) { set_kernel_text_rw(); + set_all_modules_text_rw(); return 0; } int ftrace_arch_code_modify_post_process(void) { set_kernel_text_ro(); + set_all_modules_text_ro(); return 0; } diff --git a/include/linux/module.h b/include/linux/module.h index 6cb1a3c..c6040ce 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -300,6 +300,9 @@ 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; @@ -542,6 +545,9 @@ 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) @@ -662,6 +668,13 @@ static inline int module_get_iter_tracepoints(struct tracepoint_iter *iter) return 0; } +static inline void set_all_modules_text_rw() +{ +} + +static inline void set_all_modules_text_ro() +{ +} #endif /* CONFIG_MODULES */ struct device_driver; diff --git a/kernel/module.c b/kernel/module.c index f82386b..c7fc249 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -55,6 +55,7 @@ #include #include #include +#include #define CREATE_TRACE_POINTS #include @@ -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)) @@ -1372,6 +1393,126 @@ 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) { @@ -1393,6 +1534,7 @@ 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) @@ -1405,6 +1547,7 @@ 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 @@ -1582,8 +1725,19 @@ 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"); @@ -1600,8 +1754,19 @@ 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; + } } } @@ -2382,6 +2547,18 @@ 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; @@ -2504,6 +2681,7 @@ 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/