Messages in this thread | | | Date | Wed, 07 Sep 2022 10:11:40 +0200 | From | Michael Walle <> | Subject | Re: [EXT] [RFC PATCH HBK: 0/8] HW BOUND KEY as TRUSTED KEY |
| |
Hi David,
Am 2022-09-07 09:46, schrieb David Gstir: >> On 07.09.2022, at 09:29, Michael Walle <michael@walle.cc> wrote: >> >> Am 2022-09-07 09:22, schrieb Pankaj Gupta: >>>> -----Original Message----- >>>> From: Michael Walle <michael@walle.cc> >>>> Sent: Tuesday, September 6, 2022 12:43 PM >>>> To: Pankaj Gupta <pankaj.gupta@nxp.com> >>>> Cc: jarkko@kernel.org; a.fatoum@pengutronix.de; Jason@zx2c4.com; >>>> jejb@linux.ibm.com; zohar@linux.ibm.com; dhowells@redhat.com; >>>> sumit.garg@linaro.org; david@sigma-star.at; john.ernberg@actia.se; >>>> jmorris@namei.org; serge@hallyn.com; herbert@gondor.apana.org.au; >>>> davem@davemloft.net; j.luebbe@pengutronix.de; ebiggers@kernel.org; >>>> richard@nod.at; keyrings@vger.kernel.org; >>>> linux-crypto@vger.kernel.org; >>>> linux-integrity@vger.kernel.org; linux-kernel@vger.kernel.org; >>>> linux- >>>> security-module@vger.kernel.org; Sahil Malhotra >>>> <sahil.malhotra@nxp.com>; Kshitiz Varshney >>>> <kshitiz.varshney@nxp.com>; >>>> Horia Geanta <horia.geanta@nxp.com>; Varun Sethi <V.Sethi@nxp.com> >>>> Subject: [EXT] Re: [RFC PATCH HBK: 0/8] HW BOUND KEY as TRUSTED KEY >>>> Caution: EXT Email >>>> Hi, >>>> Am 2022-09-06 08:51, schrieb Pankaj Gupta: >>>> > Hardware Bound key(HBK), is never acessible as plain key outside of >>>> > the hardware boundary. Thus, it is un-usable, even if somehow fetched >>>> > from kernel memory. It ensures run-time security. >>>> > >>>> > This patchset adds generic support for classing the Hardware Bound >>>> > Key, based on: >>>> > >>>> > - Newly added flag-'is_hbk', added to the tfm. >>>> > >>>> > Consumer of the kernel crypto api, after allocating >>>> > the transformation, sets this flag based on the basis >>>> > of the type of key consumer has. >>>> > >>>> > - This helps to influence the core processing logic >>>> > for the encapsulated algorithm. >>>> > >>>> > - This flag is set by the consumer after allocating >>>> > the tfm and before calling the function crypto_xxx_setkey(). >>>> > >>>> > First implementation is based on CAAM. >>>> > >>>> > NXP built CAAM IP is the Cryptographic Acceleration and Assurance >>>> > Module. >>>> > This is contain by the i.MX and QorIQ SoCs by NXP. >>>> > >>>> > CAAM is a suitable backend (source) for kernel trusted keys. >>>> > This backend source can be used for run-time security as well by >>>> > generating the hardware bound key. >>>> > >>>> > Along with plain key, the CAAM generates black key. A black key is an >>>> > encrypted key, which can only be decrypted inside CAAM. Hence, CAAM's >>>> > black key can only be used by CAAM. Thus it is declared as a hardware >>>> > bound key. >>>> What is the difference to the current trusted keys with CAAM? >>>> When I tested the patch series back then, I wasn't able to import a >>>> sealed >>>> key on another board with the same SoC. >>> Currently, keys that are part of trusted key-ring, contains plain >>> key. >>> With this patch-set, these key will become Hw Bound Key, which is not >>> a plain key anymore. >>> After this patch-set, if somehow the HB-key is retrieved from the >>> keyring, the retrieved key would be un-usable without hw. >> >> This doesn't answer my question why I couldn't import one key on >> another board with the same SoC. > > I don’t believe this is intended to work this way. Each key blob > created by CAAM is bound > to a specific device. Being able to decrypt the same blob on another > SoC would > open up some attack vectors: Think of a locked down device where I’m > able to > extract this key blob. Simply buying a board with the same Soc would > allow me to > decrypt this blob by copying it over to my board.
I agree, thus my first question here was, what this series is adding, if the key is already "bound" to the hardware. That is what I don't understand.
-michael
> Roughly speaking, CAAM key blobs are secure using a key derived from > the device’s master > key. This master key can be programmed via eFUSEs. So you’d have to > burn the same master > key on both SoCs and it should work. > > In any way, check the security reference manual for your SoC. It > should explain this in more detail.
| |