Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754002AbYJCRe4 (ORCPT ); Fri, 3 Oct 2008 13:34:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752792AbYJCRet (ORCPT ); Fri, 3 Oct 2008 13:34:49 -0400 Received: from mylar.outflux.net ([69.93.193.226]:40087 "EHLO mylar.outflux.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751759AbYJCRes (ORCPT ); Fri, 3 Oct 2008 13:34:48 -0400 Date: Fri, 3 Oct 2008 10:33:13 -0700 From: Kees Cook To: Jakub Jelinek Cc: Ulrich Drepper , Arjan van de Ven , Roland McGrath , linux-kernel@vger.kernel.org, libc-alpha@sourceware.org Subject: [PATCH] ELF: implement AT_RANDOM for glibc PRNG seeding Message-ID: <20081003173313.GW10632@outflux.net> References: <20081001215657.GH12527@outflux.net> <20081001220948.GC32107@sunsite.ms.mff.cuni.cz> <20081001222706.68E7E1544B4@magilla.localdomain> <20081003001616.GN10632@outflux.net> <20081003004340.GF32682@tyan-ft48-01.lab.bos.redhat.com> <20081003052938.GS10632@outflux.net> <20081002225718.6a0d803a@infradead.org> <48E5BAC6.9070007@redhat.com> <20081003145054.GU10632@outflux.net> <20081003145754.GH32682@tyan-ft48-01.lab.bos.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081003145754.GH32682@tyan-ft48-01.lab.bos.redhat.com> Organization: Canonical X-HELO: www.outflux.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3707 Lines: 105 While discussing[1] the need for glibc to have access to random bytes during program load, it seems that an earlier attempt to implement AT_RANDOM got stalled. This implements a random 16 byte string, available to every ELF program via a new auxv AT_RANDOM vector. [1] http://sourceware.org/ml/libc-alpha/2008-10/msg00006.html Signed-off-by: Kees Cook --- fs/binfmt_elf.c | 25 +++++++++++++++++++++++++ include/linux/auxvec.h | 6 +++--- 2 files changed, 28 insertions(+), 3 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 655ed8d..479a7a4 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -140,6 +140,14 @@ static int padzero(unsigned long elf_bss) #define ELF_BASE_PLATFORM NULL #endif +#ifndef ELF_AUXV_RANDOM_SIZE +/* + * AT_RANDOM provides 16 random bytes which can be used to seed + * userspace PRNGs at program load time. + */ +#define ELF_AUXV_RANDOM_SIZE 16 +#endif + static int create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, unsigned long load_addr, unsigned long interp_load_addr) @@ -152,6 +160,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, elf_addr_t __user *sp; elf_addr_t __user *u_platform; elf_addr_t __user *u_base_platform; + elf_addr_t __user *u_rand_bytes; const char *k_platform = ELF_PLATFORM; const char *k_base_platform = ELF_BASE_PLATFORM; int items; @@ -196,6 +205,18 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, return -EFAULT; } + u_rand_bytes = NULL; + if (ELF_AUXV_RANDOM_SIZE) { + unsigned char k_rand_bytes[ELF_AUXV_RANDOM_SIZE]; + get_random_bytes(k_rand_bytes, ELF_AUXV_RANDOM_SIZE); + + u_rand_bytes = (elf_addr_t __user *) + STACK_ALLOC(p, ELF_AUXV_RANDOM_SIZE); + if (__copy_to_user(u_rand_bytes, k_rand_bytes, + ELF_AUXV_RANDOM_SIZE)) + return -EFAULT; + } + /* Create the ELF interpreter info */ elf_info = (elf_addr_t *)current->mm->saved_auxv; /* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */ @@ -228,6 +249,10 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, NEW_AUX_ENT(AT_GID, tsk->gid); NEW_AUX_ENT(AT_EGID, tsk->egid); NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm)); + if (ELF_AUXV_RANDOM_SIZE) { + NEW_AUX_ENT(AT_RANDOM, + (elf_addr_t)(unsigned long)u_rand_bytes); + } NEW_AUX_ENT(AT_EXECFN, bprm->exec); if (k_platform) { NEW_AUX_ENT(AT_PLATFORM, diff --git a/include/linux/auxvec.h b/include/linux/auxvec.h index d7afa9d..d85b8f7 100644 --- a/include/linux/auxvec.h +++ b/include/linux/auxvec.h @@ -23,16 +23,16 @@ #define AT_PLATFORM 15 /* string identifying CPU for optimizations */ #define AT_HWCAP 16 /* arch dependent hints at CPU capabilities */ #define AT_CLKTCK 17 /* frequency at which times() increments */ - +/* AT_* values 18 through 22 are reserved */ #define AT_SECURE 23 /* secure mode boolean */ - #define AT_BASE_PLATFORM 24 /* string identifying real platform, may * differ from AT_PLATFORM. */ +#define AT_RANDOM 25 /* address of 16 random bytes */ #define AT_EXECFN 31 /* filename of program */ #ifdef __KERNEL__ -#define AT_VECTOR_SIZE_BASE 18 /* NEW_AUX_ENT entries in auxiliary table */ +#define AT_VECTOR_SIZE_BASE 20 /* NEW_AUX_ENT entries in auxiliary table */ /* number of "#define AT_.*" above, minus {AT_NULL, AT_IGNORE, AT_NOTELF} */ #endif -- 1.5.6.3 -- Kees Cook Ubuntu Security Team -- 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/