From patchwork Mon Jan 20 17:44:25 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Thomas_Wei=C3=9Fschuh?= X-Patchwork-Id: 13945461 Received: from todd.t-8ch.de (todd.t-8ch.de [159.69.126.157]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9DD7D1F03D0; Mon, 20 Jan 2025 17:45:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=159.69.126.157 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737395149; cv=none; b=JsTxl9z4HK3yz39TNFYyQKTmhAvYoULAEdohPr0WJX9gOJKSoB27ToLlk0IqHJZ7bjDHfR4GCkIufKJvhJD7FHfFkpXIblx/6XB9rjB7R5fzSfPK1osbUUfkog2mul0FiFZ2jtY9eKfLouwZ1DiVSEeUxiR6MSBUbR6r9aXqC1A= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737395149; c=relaxed/simple; bh=MdKjsanauiC7LwdkZFfsgUbSTeQZc+J9ZaaglNxxsks=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=tu6b7zp8RViZIY6WE8isYjG3NpUft6UiRgEn9XoicJPhVMP+1JDVHHicNjm+SOpN0fQV7krrqB2P84ReqY3uHowwFLq5nuXyscR7s1ss3CnTETWcuhKef+4zpHEhyS95g6UpEsznQ0iEjNc4qNjM4Pcv/42qKzvqYU47O7PPu1M= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=weissschuh.net; spf=pass smtp.mailfrom=weissschuh.net; dkim=pass (1024-bit key) header.d=weissschuh.net header.i=@weissschuh.net header.b=Di/M6gV2; arc=none smtp.client-ip=159.69.126.157 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=weissschuh.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=weissschuh.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=weissschuh.net header.i=@weissschuh.net header.b="Di/M6gV2" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=weissschuh.net; s=mail; t=1737395133; bh=MdKjsanauiC7LwdkZFfsgUbSTeQZc+J9ZaaglNxxsks=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=Di/M6gV2PZR/Y+ULPHNpx2nP0AYRmpRur97hFwzhHG9qZT82EnocNOEeA3rqp3lz0 h2+5CUwBdmHujmMocjg40PdHqjw5a1g3xHKKAaNvJi5l5iniwzPm4ALjx8K8HosPA8 5uUlyHHmdUAigVH4CGaYEfN3OXur5Xhu8uUM9F6U= From: =?utf-8?q?Thomas_Wei=C3=9Fschuh?= Date: Mon, 20 Jan 2025 18:44:25 +0100 Subject: [PATCH v2 6/6] module: Introduce hash-based integrity checking Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-Id: <20250120-module-hashes-v2-6-ba1184e27b7f@weissschuh.net> References: <20250120-module-hashes-v2-0-ba1184e27b7f@weissschuh.net> In-Reply-To: <20250120-module-hashes-v2-0-ba1184e27b7f@weissschuh.net> To: Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Arnd Bergmann , Luis Chamberlain , Petr Pavlu , Sami Tolvanen , Daniel Gomez , Paul Moore , James Morris , "Serge E. Hallyn" , Jonathan Corbet Cc: =?utf-8?q?Fabian_Gr=C3=BCnbichler?= , Arnout Engelen , Mattia Rizzolo , kpcyrd , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-modules@vger.kernel.org, linux-security-module@vger.kernel.org, linux-doc@vger.kernel.org, =?utf-8?q?Thomas_Wei=C3=9Fschuh?= X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1737395132; l=14935; i=linux@weissschuh.net; s=20221212; h=from:subject:message-id; bh=MdKjsanauiC7LwdkZFfsgUbSTeQZc+J9ZaaglNxxsks=; b=5IcmE9REX+FAANRF1h1BOnurKOwOaYMYqcpINOm6mCBcRkcTSJcMrGzt0fX37CpcqtYiEvLc0 1QQkiSWcpjND1eqQ23aAdahsCJmu7W0HC8zogLdLsmo3NKJQWBIePjD X-Developer-Key: i=linux@weissschuh.net; a=ed25519; pk=KcycQgFPX2wGR5azS7RhpBqedglOZVgRPfdFSPB1LNw= The current signature-based module integrity checking has some drawbacks in combination with reproducible builds: Either the module signing key is generated at build time, which makes the build unreproducible, or a static key is used, which precludes rebuilds by third parties and makes the whole build and packaging process much more complicated. Introduce a new mechanism to ensure only well-known modules are loaded by embedding a list of hashes of all modules built as part of the full kernel build into vmlinux. Non-builtin modules can be validated as before through signatures. Signed-off-by: Thomas Weißschuh --- .gitignore | 1 + Documentation/kbuild/reproducible-builds.rst | 5 ++- Makefile | 8 ++++- include/asm-generic/vmlinux.lds.h | 11 ++++++ include/linux/module_hashes.h | 17 +++++++++ kernel/module/Kconfig | 17 ++++++++- kernel/module/Makefile | 1 + kernel/module/hashes.c | 52 ++++++++++++++++++++++++++++ kernel/module/internal.h | 1 + kernel/module/main.c | 6 ++++ scripts/Makefile.modfinal | 6 ++++ scripts/Makefile.vmlinux | 5 +++ scripts/link-vmlinux.sh | 25 ++++++++++++- scripts/module-hashes.sh | 26 ++++++++++++++ security/lockdown/Kconfig | 2 +- 15 files changed, 178 insertions(+), 5 deletions(-) diff --git a/.gitignore b/.gitignore index 6839cf84acda0d2d3c236a2e42b0cb0fe1b14965..7c40151c3f5d0c15ac04cead5f21c291a98d779f 100644 --- a/.gitignore +++ b/.gitignore @@ -28,6 +28,7 @@ *.gz *.i *.ko +*.ko.hash *.lex.c *.ll *.lst diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst index f2dcc39044e66ddd165646e0b51ccb0209aca7dd..6a742ad745113a9267223b33810dbc7218c47d4c 100644 --- a/Documentation/kbuild/reproducible-builds.rst +++ b/Documentation/kbuild/reproducible-builds.rst @@ -79,7 +79,10 @@ generate a different temporary key for each build, resulting in the modules being unreproducible. However, including a signing key with your source would presumably defeat the purpose of signing modules. -One approach to this is to divide up the build process so that the +Instead ``CONFIG_MODULE_HASHES`` can be used to embed a static list +of valid modules to load. + +Another approach to this is to divide up the build process so that the unreproducible parts can be treated as sources: 1. Generate a persistent signing key. Add the certificate for the key diff --git a/Makefile b/Makefile index b9464c88ac7230518a756bff5e6c5c8871cc5058..fc862ffd2df843c0b68bebc8f554b88850ba1541 100644 --- a/Makefile +++ b/Makefile @@ -1535,8 +1535,10 @@ endif # is an exception. ifdef CONFIG_DEBUG_INFO_BTF_MODULES KBUILD_BUILTIN := 1 +ifndef CONFIG_MODULE_HASHES modules: vmlinux endif +endif modules: modules_prepare @@ -1916,7 +1918,11 @@ modules.order: $(build-dir) # KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules. # This is solely useful to speed up test compiles. modules: modpost -ifneq ($(KBUILD_MODPOST_NOFINAL),1) +ifdef CONFIG_MODULE_HASHES +ifeq ($(MODULE_HASHES_MODPOST_FINAL), 1) + $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal +endif +else ifneq ($(KBUILD_MODPOST_NOFINAL),1) $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal endif diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 54504013c74915c2ed923fb3afde024a69cdae6b..aebea528aac3d7209bcee12c25f750ab0f7576a5 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -486,6 +486,8 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) \ PRINTK_INDEX \ \ + MODULE_HASHES \ + \ /* Kernel symbol table: Normal symbols */ \ __ksymtab : AT(ADDR(__ksymtab) - LOAD_OFFSET) { \ __start___ksymtab = .; \ @@ -895,6 +897,15 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) #define PRINTK_INDEX #endif +#ifdef CONFIG_MODULE_HASHES +#define MODULE_HASHES \ + .module_hashes : AT(ADDR(.module_hashes) - LOAD_OFFSET) { \ + BOUNDED_SECTION_BY(.module_hashes, _module_hashes) \ + } +#else +#define MODULE_HASHES +#endif + /* * Discard .note.GNU-stack, which is emitted as PROGBITS by the compiler. * Otherwise, the type of .notes section would become PROGBITS instead of NOTES. diff --git a/include/linux/module_hashes.h b/include/linux/module_hashes.h new file mode 100644 index 0000000000000000000000000000000000000000..5f2f0546e3875e6bc73bdd53aebaada7371b7f79 --- /dev/null +++ b/include/linux/module_hashes.h @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ + +#ifndef _LINUX_MODULE_HASHES_H +#define _LINUX_MODULE_HASHES_H + +#include +#include +#include + +#define __module_hashes_section __section(".module_hashes") +#define MODULE_HASHES_HASH_SIZE SHA256_DIGEST_SIZE + +extern const u8 module_hashes[][MODULE_HASHES_HASH_SIZE]; + +extern const typeof(module_hashes[0]) __start_module_hashes, __stop_module_hashes; + +#endif /* _LINUX_MODULE_HASHES_H */ diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig index a80de8d22efdd0f13b3eb579a8ff1e69029d0694..cdd30b9a08d8cdf3ec0595b5e414265b869d343e 100644 --- a/kernel/module/Kconfig +++ b/kernel/module/Kconfig @@ -212,7 +212,7 @@ config MODULE_SIG config MODULE_SIG_POLICY def_bool y - depends on MODULE_SIG + depends on MODULE_SIG || MODULE_HASHES config MODULE_SIG_FORCE bool "Require modules to be validly signed" @@ -348,6 +348,21 @@ config MODULE_DECOMPRESS If unsure, say N. +config MODULE_HASHES + bool "Module hash validation" + depends on $(success,cksum --algorithm sha256 --raw /dev/null) + select CRYPTO_LIB_SHA256 + help + Validate modules by their hashes. + Only modules built together with the main kernel image can be + validated that way. + + This is a reproducible-build compatible alternative to a build-time + generated module keyring, as enabled by + CONFIG_MODULE_SIG_KEY=certs/signing_key.pem. + + Also see the warning in MODULE_SIG about stripping modules. + config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS bool "Allow loading of modules with missing namespace imports" help diff --git a/kernel/module/Makefile b/kernel/module/Makefile index 50ffcc413b54504db946af4dce3b41dc4aece1a5..6fe0c14ca5a05b49c1161fcfa8aaa130f89b70e1 100644 --- a/kernel/module/Makefile +++ b/kernel/module/Makefile @@ -23,3 +23,4 @@ obj-$(CONFIG_KGDB_KDB) += kdb.o obj-$(CONFIG_MODVERSIONS) += version.o obj-$(CONFIG_MODULE_UNLOAD_TAINT_TRACKING) += tracking.o obj-$(CONFIG_MODULE_STATS) += stats.o +obj-$(CONFIG_MODULE_HASHES) += hashes.o diff --git a/kernel/module/hashes.c b/kernel/module/hashes.c new file mode 100644 index 0000000000000000000000000000000000000000..1aa49767a39b4e0c495b17d3f2edcb5a6ceb839e --- /dev/null +++ b/kernel/module/hashes.c @@ -0,0 +1,52 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#define pr_fmt(fmt) "module/hash: " fmt + +#include +#include +#include +#include +#include "internal.h" + +static inline size_t module_hashes_count(void) +{ + return (__stop_module_hashes - __start_module_hashes) / MODULE_HASHES_HASH_SIZE; +} + +static __init __maybe_unused int module_hashes_init(void) +{ + size_t num_hashes = module_hashes_count(); + int num_width = (intlog10(num_hashes) >> 24) + 1; + size_t i; + + pr_debug("Known hashes (%zu):\n", num_hashes); + + for (i = 0; i < num_hashes; i++) + pr_debug("%*zu %*phN\n", num_width, i, + (int)sizeof(module_hashes[i]), module_hashes[i]); + + return 0; +} + +#if IS_ENABLED(CONFIG_MODULE_DEBUG) +early_initcall(module_hashes_init); +#endif + +int module_hash_check(struct load_info *info, int flags) +{ + u8 digest[MODULE_HASHES_HASH_SIZE]; + size_t i; + + sha256((const u8 *)info->hdr, info->len, digest); + + for (i = 0; i < module_hashes_count(); i++) { + if (memcmp(module_hashes[i], digest, MODULE_HASHES_HASH_SIZE) == 0) { + pr_debug("allow %*phN\n", (int)sizeof(digest), digest); + info->sig_ok = true; + return 0; + } + } + + pr_debug("block %*phN\n", (int)sizeof(digest), digest); + return -ENOKEY; +} diff --git a/kernel/module/internal.h b/kernel/module/internal.h index c30abeefa60b884c4a69b1eb4f1123a4bbee4b47..9c927c212f862fff7000f1cfac3c7e391a2390ac 100644 --- a/kernel/module/internal.h +++ b/kernel/module/internal.h @@ -334,6 +334,7 @@ int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs, char *secstrings, struct module *mod); int module_sig_check(struct load_info *info, int flags); +int module_hash_check(struct load_info *info, int flags); #ifdef CONFIG_DEBUG_KMEMLEAK void kmemleak_load_module(const struct module *mod, const struct load_info *info); diff --git a/kernel/module/main.c b/kernel/module/main.c index effe1db02973d4f60ff6cbc0d3b5241a3576fa3e..094ace81d795711b56d12a2abc75ea35449c8300 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -3218,6 +3218,12 @@ static int module_integrity_check(struct load_info *info, int flags) { int err = 0; + if (IS_ENABLED(CONFIG_MODULE_HASHES)) { + err = module_hash_check(info, flags); + if (!err) + return 0; + } + if (IS_ENABLED(CONFIG_MODULE_SIG)) err = module_sig_check(info, flags); diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal index 5d01b553ec9a4565c8e5a6edd05665c409003bc1..080b4fc3a9ba5036b45f04a7e79f2fc02364f93a 100644 --- a/scripts/Makefile.modfinal +++ b/scripts/Makefile.modfinal @@ -43,6 +43,9 @@ quiet_cmd_btf_ko = BTF [M] $@ $(RESOLVE_BTFIDS) -b $(objtree)/vmlinux $@; \ fi; +quiet_cmd_cksum_ko = + cmd_cksum_ko = cksum --algorithm sha256 --raw $@ > $@.hash + # Same as newer-prereqs, but allows to exclude specified extra dependencies newer_prereqs_except = $(filter-out $(PHONY) $(1),$?) @@ -57,6 +60,9 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \ ifdef CONFIG_DEBUG_INFO_BTF_MODULES +$(if $(newer-prereqs),$(call cmd,btf_ko)) endif +ifdef CONFIG_MODULE_HASHES + $(call cmd,cksum_ko) +endif targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o) .module-common.o diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux index 873caaa553134e09d034e0c4e0ac7f07c9e3f31b..4b6ba03cdd5e4faad30a0b533407955c542c7a20 100644 --- a/scripts/Makefile.vmlinux +++ b/scripts/Makefile.vmlinux @@ -79,6 +79,11 @@ ifdef CONFIG_DEBUG_INFO_BTF vmlinux: $(RESOLVE_BTFIDS) endif +ifdef CONFIG_MODULE_HASHES +vmlinux: $(srctree)/scripts/module-hashes.sh +vmlinux: modules.order +endif + # module.builtin.ranges # --------------------------------------------------------------------------- ifdef CONFIG_BUILTIN_MODULE_RANGES diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index 803c8d6f35a7f29fb68b29afa8546f4dde0bd4cb..db072e4e5d6581453a009a9e837042ba28a138ce 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -104,7 +104,7 @@ vmlinux_link() ${ld} ${ldflags} -o ${output} \ ${wl}--whole-archive ${objs} ${wl}--no-whole-archive \ ${wl}--start-group ${libs} ${wl}--end-group \ - ${kallsymso} ${btf_vmlinux_bin_o} ${arch_vmlinux_o} ${ldlibs} + ${kallsymso} ${btf_vmlinux_bin_o} ${module_hashes_o} ${arch_vmlinux_o} ${ldlibs} } # generate .BTF typeinfo from DWARF debuginfo @@ -215,6 +215,7 @@ fi btf_vmlinux_bin_o= kallsymso= +module_hashes_o= strip_debug= if is_enabled CONFIG_KALLSYMS; then @@ -222,6 +223,17 @@ if is_enabled CONFIG_KALLSYMS; then kallsyms .tmp_vmlinux0.syms .tmp_vmlinux0.kallsyms fi +if is_enabled CONFIG_MODULE_HASHES; then + # At this point the hashes are still wrong. + # This step reserves the exact amount of space for the objcopy step + # after BTF generation. + ${srctree}/scripts/module-hashes.sh prealloc > .tmp_module_hashes.c + module_hashes_o=.tmp_module_hashes.o + info CC ${module_hashes_o} + ${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} ${KBUILD_CFLAGS} \ + ${KBUILD_CFLAGS_KERNEL} -c -o "${module_hashes_o}" ".tmp_module_hashes.c" +fi + if is_enabled CONFIG_KALLSYMS || is_enabled CONFIG_DEBUG_INFO_BTF; then # The kallsyms linking does not need debug symbols, but the BTF does. @@ -302,6 +314,17 @@ if is_enabled CONFIG_BUILDTIME_TABLE_SORT; then fi fi +if is_enabled CONFIG_MODULE_HASHES; then + info MAKE modules + ${MAKE} -f Makefile MODULE_HASHES_MODPOST_FINAL=1 modules + ${srctree}/scripts/module-hashes.sh > .tmp_module_hashes.c + info CC ${module_hashes_o} + ${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} ${KBUILD_CFLAGS} \ + ${KBUILD_CFLAGS_KERNEL} -c -o "${module_hashes_o}" ".tmp_module_hashes.c" + ${OBJCOPY} --dump-section .module_hashes=.tmp_module_hashes.bin ${module_hashes_o} + ${OBJCOPY} --update-section .module_hashes=.tmp_module_hashes.bin vmlinux +fi + # step a (see comment above) if is_enabled CONFIG_KALLSYMS; then if ! cmp -s System.map "${kallsyms_sysmap}"; then diff --git a/scripts/module-hashes.sh b/scripts/module-hashes.sh new file mode 100755 index 0000000000000000000000000000000000000000..120ce924105c51cdd7a704cbec7e5fa356f9ce1a --- /dev/null +++ b/scripts/module-hashes.sh @@ -0,0 +1,26 @@ +#!/bin/bash +# SPDX-License-Identifier: GPL-2.0-or-later + +set -e +set -u +set -o pipefail + +prealloc="${1:-}" + +echo "#include " +echo +echo "const u8 module_hashes[][MODULE_HASHES_HASH_SIZE] __module_hashes_section = {" + +for mod in $(< modules.order); do + mod="${mod/%.o/.ko}" + if [ "$prealloc" = "prealloc" ]; then + modhash="" + else + modhash="$(cat "$mod".hash | hexdump -v -e '"0x" 1/1 "%02x, "')" + fi + echo -e "\t/* $mod */" + echo -e "\t{ $modhash}," + echo +done + +echo "};" diff --git a/security/lockdown/Kconfig b/security/lockdown/Kconfig index 155959205b8eac2c85897a8c4c8b7ec471156706..60b240e3ef1f9609e3f3241befc0bbc7e4a3db74 100644 --- a/security/lockdown/Kconfig +++ b/security/lockdown/Kconfig @@ -1,7 +1,7 @@ config SECURITY_LOCKDOWN_LSM bool "Basic module for enforcing kernel lockdown" depends on SECURITY - depends on !MODULES || MODULE_SIG + depends on !MODULES || MODULE_SIG || MODULE_HASHES help Build support for an LSM that enforces a coarse kernel lockdown behaviour.