Hi! Mimi Zohar writes: > On Mon, 2015-11-09 at 16:18 +0100, Steffen Trumtrar wrote: >> Hi! >> >> The RFC Patch attached after this cover letter is mostly for illustration >> purposes, so please don't waste too much time reviewing the code ;-) >> >> For context I'll try to describe the problem that this patch tries to solve. >> >> I need to be able to boot an EVM signed (and dongled) rootfs. The CAAM on >> the i.MX6 has support for an OTP key and can en/decrypt data. >> It also has a feature for generating red blobs: basically a chunk of data, >> that is encrypted with the OTP key, which can be saved on some medium as a >> secret to decrypt the EVM HMAC secret for one specific device. >> >> To open the rootfs, the secret is handed from the bootloader to the kernel >> as a base64 encoded string via the cmdline to an initramfs. >> In the initramfs the sysfs file "modifier" is set to something starting with >> "kernel:evm" and the base64 string is written to the sysfs file "blob". >> The CAAM than decodes the red blob and, in case of "kernel:evm", initializes >> the EVM or otherwise writes the result to "payload" if the modifier starts >> with "user:". Therefore a blob that was generated for EVM never leaves the >> kernel on decryption. >> Generation of blobs goes like: echoing "modifier" to something and echoing >> the payload to "payload". The red blob can than be read from "blob". >> >> >> So, the sysfs interface is not the best option, I guess. The question is: >> What is the right approach for a setup like this? >> I need to: >> - be able to encrypt the secret and store it somewhere >> - to load the stored secret and decrypt it later >> - initialize IMA/EVM with the secret >> >> Would something like >> - security/keys/encrypted-keys/encrypted.c >> be the correct approach? > > Instead of using the CAAM for OTP encrypting/decrypting, can it be used > to load the EVM key directly? Dmitry's patches, which will be > upstreamed in 4.5 > https://git.kernel.org/cgit/linux/kernel/git/zohar/linux-integrity.git/log/?h=for-next-4.5? adds support for a crypto device to directly load the EVM key. > The patches look good and I use them for loading the EVM key from the CAAM driver. But I still need the OTP decryption functionality. The key data that I hand to evm_set_key must be device specific but I don't want to use the fused OTP in the CAAM directly. The OTP is used to protect multiple random keys. Therefore I need to generate encrypted blobs that I can store on some unsecure memory (EEPROM, NAND,...) and be able to hand that later back to the CAAM module, to then get back an IMA/EVM, ecryptfs, $something key. > FYI, the EVM key is an encrypted key, which encrypts/decrypts either a > trusted or user type key. > So the normal approach would be to have a key in the kernel keyring and decrypt it with the key loaded with evm_set_key? Can I somehow use the keyring framework as an abstraction around my blobbing/deblobbing functionality? So that the "keyring" calls into the crypto driver to decrypt the data and uses the crypto driver to encrypt the keys when I want to "dump" them? Thanks, Steffen -- Pengutronix e.K. | Steffen Trumtrar | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
