From 4da8f8c8a1e07ad18f057f4044ad96f4135dc877 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Micka=C3=ABl=20Sala=C3=BCn?= Date: Fri, 23 Oct 2020 19:05:12 +0200 Subject: [PATCH] dm verity: Add support for signature verification with 2nd keyring MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Add a new configuration DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING to enable dm-verity signatures to be verified against the secondary trusted keyring. Instead of relying on the builtin trusted keyring (with hard-coded certificates), the second trusted keyring can include certificate authorities from the builtin trusted keyring and child certificates loaded at run time. Using the secondary trusted keyring enables to use dm-verity disks (e.g. loop devices) signed by keys which did not exist at kernel build time, leveraging the certificate chain of trust model. In practice, this makes it possible to update certificates without kernel update and reboot, aligning with module and kernel (kexec) signature verification which already use the secondary trusted keyring. Signed-off-by: Mickaël Salaün Signed-off-by: Mike Snitzer --- Documentation/admin-guide/device-mapper/verity.rst | 7 ++++++- drivers/md/Kconfig | 13 ++++++++++++- drivers/md/dm-verity-verify-sig.c | 9 +++++++-- 3 files changed, 25 insertions(+), 4 deletions(-) diff --git a/Documentation/admin-guide/device-mapper/verity.rst b/Documentation/admin-guide/device-mapper/verity.rst index 66f71f0..b088a64 100644 --- a/Documentation/admin-guide/device-mapper/verity.rst +++ b/Documentation/admin-guide/device-mapper/verity.rst @@ -134,7 +134,12 @@ root_hash_sig_key_desc the pkcs7 signature of the roothash. The pkcs7 signature is used to validate the root hash during the creation of the device mapper block device. Verification of roothash depends on the config DM_VERITY_VERIFY_ROOTHASH_SIG - being set in the kernel. + being set in the kernel. The signatures are checked against the builtin + trusted keyring by default, or the secondary trusted keyring if + DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING is set. The secondary + trusted keyring includes by default the builtin trusted keyring, and it can + also gain new certificates at run time if they are signed by a certificate + already in the secondary trusted keyring. Theory of operation =================== diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig index 30ba357..1d68935 100644 --- a/drivers/md/Kconfig +++ b/drivers/md/Kconfig @@ -530,11 +530,22 @@ config DM_VERITY_VERIFY_ROOTHASH_SIG bool "Verity data device root hash signature verification support" depends on DM_VERITY select SYSTEM_DATA_VERIFICATION - help + help Add ability for dm-verity device to be validated if the pre-generated tree of cryptographic checksums passed has a pkcs#7 signature file that can validate the roothash of the tree. + By default, rely on the builtin trusted keyring. + + If unsure, say N. + +config DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING + bool "Verity data device root hash signature verification with secondary keyring" + depends on DM_VERITY_VERIFY_ROOTHASH_SIG + depends on SECONDARY_TRUSTED_KEYRING + help + Rely on the secondary trusted keyring to verify dm-verity signatures. + If unsure, say N. config DM_VERITY_FEC diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c index 614e43d..29385dc 100644 --- a/drivers/md/dm-verity-verify-sig.c +++ b/drivers/md/dm-verity-verify-sig.c @@ -119,8 +119,13 @@ int verity_verify_root_hash(const void *root_hash, size_t root_hash_len, } ret = verify_pkcs7_signature(root_hash, root_hash_len, sig_data, - sig_len, NULL, VERIFYING_UNSPECIFIED_SIGNATURE, - NULL, NULL); + sig_len, +#ifdef CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG_SECONDARY_KEYRING + VERIFY_USE_SECONDARY_KEYRING, +#else + NULL, +#endif + VERIFYING_UNSPECIFIED_SIGNATURE, NULL, NULL); return ret; } -- 2.7.4