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.
Interest has been proclaimed by NixOS, Arch Linux, Proxmox, SUSE and the general reproducible builds community. To properly test the reproducibility in combination with CONFIG_INFO_BTF another patch or pahole v1.29 is needed: "[PATCH bpf-next] kbuild, bpf: Enable reproducible BTF generation" [0] Questions for current patch: * Naming * Can the number of built-in modules be retrieved while building kernel/module/hashes.o? This would remove the need for the preallocation step in link-vmlinux.sh. * How should this interaction with IMA? Further improvements: * Use a LSM/IMA Keyring to store and validate hashes * Use MODULE_SIG_HASH for configuration * UAPI for discovery? * Currently has a permanent memory overhead [0] https://lore.kernel.org/lkml/20241211-pahole-reproducible-v1-1-22feae19b...@weissschuh.net/ Signed-off-by: Thomas Weißschuh <li...@weissschuh.net> --- Changes in v3: - Rebase on v6.15-rc1 - Use openssl to calculate hash - Avoid warning if no modules are built - Simplify module_integrity_check() a bit - Make incompatibility with INSTALL_MOD_STRIP explicit - Update docs - Add IMA cleanups - Link to v2: https://lore.kernel.org/r/20250120-module-hashes-v2-0-ba1184e27...@weissschuh.net Changes in v2: - Drop RFC state - Mention interested parties in cover letter - Expand Kconfig description - Add compatibility with CONFIG_MODULE_SIG - Parallelize module-hashes.sh - Update Documentation/kbuild/reproducible-builds.rst - Link to v1: https://lore.kernel.org/r/20241225-module-hashes-v1-0-d710ce7a3...@weissschuh.net --- Thomas Weißschuh (9): powerpc/ima: Drop unnecessary check for CONFIG_MODULE_SIG ima: efi: Drop unnecessary check for CONFIG_MODULE_SIG/CONFIG_KEXEC_SIG kbuild: add stamp file for vmlinux BTF data kbuild: generate module BTF based on vmlinux.unstripped module: Make module loading policy usable without MODULE_SIG module: Move integrity checks into dedicated function module: Move lockdown check into generic module loader lockdown: Make the relationship to MODULE_SIG a dependency module: Introduce hash-based integrity checking .gitignore | 1 + Documentation/kbuild/reproducible-builds.rst | 5 ++- Makefile | 8 +++- arch/powerpc/kernel/ima_arch.c | 3 +- include/asm-generic/vmlinux.lds.h | 11 ++++++ include/linux/module.h | 8 ++-- include/linux/module_hashes.h | 17 +++++++++ kernel/module/Kconfig | 21 ++++++++++- kernel/module/Makefile | 1 + kernel/module/hashes.c | 56 ++++++++++++++++++++++++++++ kernel/module/internal.h | 8 +--- kernel/module/main.c | 51 ++++++++++++++++++++++--- kernel/module/signing.c | 24 +----------- scripts/Makefile.modfinal | 18 ++++++--- scripts/Makefile.modinst | 4 ++ scripts/Makefile.vmlinux | 5 +++ scripts/link-vmlinux.sh | 31 ++++++++++++++- scripts/module-hashes.sh | 26 +++++++++++++ security/integrity/ima/ima_efi.c | 6 +-- security/lockdown/Kconfig | 2 +- 20 files changed, 250 insertions(+), 56 deletions(-) --- base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8 change-id: 20241225-module-hashes-7a50a7cc2a30 Best regards, -- Thomas Weißschuh <li...@weissschuh.net>
