Hi Roberto, On 2025-01-21 11:26:29+0100, Roberto Sassu wrote: > On Mon, 2025-01-20 at 18:44 +0100, Thomas Weißschuh wrote: > > 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 is needed: > > "[PATCH bpf-next] kbuild, bpf: Enable reproducible BTF generation" [0] > > (If you happen to test that one, please give some feedback) > > > > 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. > > > > Further improvements: > > * Use a LSM/IMA/Keyring to store and validate hashes > > + linux-integrity, Mimi > > Hi Thomas > > I developed something related to it, it is called Integrity Digest > Cache [1]. Thanks for the pointer. > It has the ability to store in the kernel memory a cache of digests > extracted from a file (or if desired in the future, from a reserved > area in the kernel image). > > It exposes an API to query a digest (get/lookup/put) from a digest > cache and to verify whether or not the integrity of the file digests > were extracted from was verified by IMA or another LSM > (verif_set/verif_get). I see how this could be used together with the module hashes. For now I think both features should be developed independently. Integrating them will require some extra code and coordination. While the current linear, unsorted list of hashes used by my code may be slightly inefficient, it shouldn't matter in practize as the hash validation is only a bunch of memcmp()s over a contiguous chunk of memory, which is very cheap. When both features are well established we can look at integrating them. At least a build-time userspace generator of a digest cache would be necessary. And due to the current implementation details it would be necessary to estimate the size of a static digest cache more or less exactly by its number of elements alone. Thomas > [1]: https://lore.kernel.org/linux-integrity/20241119104922.2772571-1-roberto.sassu@xxxxxxxxxxxxxxx/ > > > * Use MODULE_SIG_HASH for configuration > > * UAPI for discovery? > > > > [0] https://lore.kernel.org/lkml/20241211-pahole-reproducible-v1-1-22feae19bad9@xxxxxxxxxxxxxx/ > > > > Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx> > > --- > > 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-d710ce7a3fd1@xxxxxxxxxxxxxx > > > > --- > > Thomas Weißschuh (6): > > kbuild: add stamp file for vmlinux BTF data > > 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 ++++- > > 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 | 52 +++++++++++++++++++++++++++ > > kernel/module/internal.h | 8 +---- > > kernel/module/main.c | 54 +++++++++++++++++++++++++--- > > kernel/module/signing.c | 24 +------------ > > scripts/Makefile.modfinal | 10 ++++-- > > scripts/Makefile.vmlinux | 5 +++ > > scripts/link-vmlinux.sh | 31 +++++++++++++++- > > scripts/module-hashes.sh | 26 ++++++++++++++ > > security/lockdown/Kconfig | 2 +- > > 17 files changed, 238 insertions(+), 46 deletions(-) > > --- > > base-commit: 2cd5917560a84d69dd6128b640d7a68406ff019b > > change-id: 20241225-module-hashes-7a50a7cc2a30 > > > > Best regards, >
