On Fri, 2019-06-07 at 16:40 +0200, Roberto Sassu wrote: > > On Thu, 2019-06-06 at 13:26 +0200, Roberto Sassu wrote: > >> Although this choice appears legitimate, it might not be suitable for > >> hardened systems, where the administrator expects that access is denied if > >> there is any error. An attacker could intentionally delete the EVM keys > >> from the system and set the file digest in security.ima to the actual file > >> digest so that the final appraisal status is INTEGRITY_PASS. > > > > Assuming that the EVM HMAC key is stored in the initramfs, not on some > > other file system, and the initramfs is signed, INTEGRITY_UNKNOWN > > would be limited to the rootfs filesystem. > > There is another issue. The HMAC key, like the public keys, should be > loaded when appraisal is disabled. This means that we have to create a > trusted key at early boot and defer the unsealing. There is no need for IMA to appraise the public key file signature, since the certificate is signed by a key on the builtin/secondary trusted keyring. With CONFIG_IMA_LOAD_X509 enabled, the public key can be loaded onto the IMA keyring with IMA-appraisal enabled, but without verifying the file signature. Mimi
