IMA extends Platform Configuration Registers (PCRs) of the TPM to give a proof to a remote verifier that the measurement list contains all measurements done by the kernel and that the list was not maliciously modified by an attacker. IMA was originally designed to extend PCRs with a SHA1 digest, provided with the measurement list, and was subsequently updated to extend all PCR banks in case a TPM 2.0 is used. Non-SHA1 PCR banks are not supposed to be used for remote attestation, as they are extended with a SHA1 digest padded with zeros, which does not increase the strength. This patch set addresses this issue by extending PCRs with the digest of the measurement entry calculated with the crypto subsystem. The list of algorithms used to calculate the digest are taken from ima_tpm_chip->allocated_banks, returned by the TPM driver. The SHA1 digest is always calculated, as SHA1 still remains the default algorithm for the template digest in the measurement list. This patch set also makes two additional modifications related to the usage of hash algorithms. First, since now the template digest for the default IMA algorithm is always calculated, this is used for hash collision detection, to check if there are duplicate measurement entries. Second, it uses the default IMA hash algorithm to calculate the boot aggregate, assuming that the corresponding PCR bank is currently allocated. Otherwise, it finds the first PCR bank for which the crypto ID is known. IMA initialization fails only if no algorithm known to the crypto subsystem is found. This patch set does not yet modify the format of the measurement list to provide the digests passed to the TPM. However, reconstructing the value of the quoted PCR is still possible for the verifier by calculating the digest on measurement data found in binary_runtime_measurements. The attest-tools library [1] has been updated to verify non-SHA1 PCR banks [2] and to handle non-SHA1 boot aggregate [3]. [1] https://github.com/euleros/attest-tools/tree/0.2-devel [2] https://github.com/euleros/attest-tools/commit/282a0b1a5e6d9c87adf21561018528d7bbdc7f38 [3] https://github.com/euleros/attest-tools/commit/3a4c8e250fde7661257aba022d677bf0af5399da Roberto Sassu (8): tpm: initialize crypto_id of allocated_banks to HASH_ALGO__LAST ima: evaluate error in init_ima() ima: store template digest directly in ima_template_entry ima: switch to dynamically allocated buffer for template digests ima: allocate and initialize tfm for each PCR bank ima: calculate and extend PCR with digests in ima_template_entry ima: use ima_hash_algo for collision detection in the measurement list ima: switch to ima_hash_algo for boot aggregate drivers/char/tpm/tpm2-cmd.c | 2 + security/integrity/ima/ima.h | 7 +- security/integrity/ima/ima_api.c | 20 ++- security/integrity/ima/ima_crypto.c | 219 ++++++++++++++++++++------ security/integrity/ima/ima_fs.c | 4 +- security/integrity/ima/ima_init.c | 6 +- security/integrity/ima/ima_main.c | 6 + security/integrity/ima/ima_queue.c | 36 +++-- security/integrity/ima/ima_template.c | 22 ++- 9 files changed, 241 insertions(+), 81 deletions(-) -- 2.17.1
