Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753325AbZIKCur (ORCPT ); Thu, 10 Sep 2009 22:50:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752432AbZIKCuq (ORCPT ); Thu, 10 Sep 2009 22:50:46 -0400 Received: from mail-yw0-f174.google.com ([209.85.211.174]:34234 "EHLO mail-yw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752401AbZIKCup (ORCPT ); Thu, 10 Sep 2009 22:50:45 -0400 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=Ksz1JD3HRA+cyDH560RvcyHLpdr4+4Tost2JUGQV5a1m/XC/zwqLdXWNlkWTsuNVvJ n+vlXd8VrHE+9h54vf+BMqmK+3LB6Q1iV3nLFpRoU7qaEdnPrWdRcCi8Ot6vIzLrHLf2 Xu6y7fJWaLQ+cbIGNY2LGR5UlkBul7kaj1API= MIME-Version: 1.0 Date: Thu, 10 Sep 2009 22:50:47 -0400 Message-ID: <817ecb6f0909101950v2fc6dc6u5cbc40cd9a9dde77@mail.gmail.com> Subject: [PATCH v6] 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 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: 8042 Lines: 260 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 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 sections to ensure that each page contains only one type of content. RO/NX enforcement is active on x86 only. 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 The patch have been developed for Linux 2.6.30 by Siarhei Liakh and Xuxian Jiang . --- Signed-off-by: Siarhei Liakh Signed-off-by: Xuxian Jiang Acked-by: Arjan van de Ven 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..660278a 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -52,6 +52,7 @@ #include #include #include +#include #if 0 #define DEBUGP printk @@ -63,6 +64,26 @@ #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_RODATA=y + */ +#ifdef CONFIG_DEBUG_RODATA +#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)) @@ -1471,6 +1492,69 @@ static int __unlink_module(void *_mod) return 0; } +/* + * LKM RO/NX protection: protect module's text/ro-data + * from modification and any data from execution. + */ +static void set_section_ro_nx(void *base, + unsigned long text_size, + unsigned long ro_size, + unsigned long total_size) +{ +#ifdef CONFIG_X86 + /* 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) { + begin_pfn = PFN_DOWN((unsigned long)base); + end_pfn = PFN_DOWN((unsigned long)base + ro_size); + if (end_pfn > begin_pfn) + set_memory_ro(begin_pfn << PAGE_SHIFT, + end_pfn - begin_pfn); + } + + /* + * 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); + } +#endif +} + +/* Setting memory back to RW+NX before releasing it */ +void unset_section_ro_nx(struct module *mod, void *module_region) +{ +#ifdef CONFIG_X86 + 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); + } +#endif +} + /* Free a module, remove from lists, etc (must hold module_mutex). */ static void free_module(struct module *mod) { @@ -1493,6 +1577,7 @@ static void free_module(struct module *mod) ftrace_release(mod->module_core, mod->core_size); /* 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) @@ -1505,6 +1590,7 @@ 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); } @@ -1678,8 +1764,19 @@ 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"); @@ -1696,8 +1793,19 @@ 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; + } } } @@ -2291,6 +2399,18 @@ 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(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; @@ -2394,6 +2514,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod, mutex_lock(&module_mutex); /* Drop initial reference. */ module_put(mod); + 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/