linux-kernel - RE: [EXT] Re: [RFC PATCH HBK: 0/8] HW BOUND KEY as TRUSTED KEY

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Message-ID: <DU2PR04MB863055712C4D919D7892AAC795419@DU2PR04MB8630.eurprd04.prod.outlook.com>
Date:   Wed, 7 Sep 2022 09:57:55 +0000
From:   Pankaj Gupta <pankaj.gupta@....com>
To:     "jlu@...gutronix.de" <jlu@...gutronix.de>,
        Jarkko Sakkinen <jarkko@...nel.org>
CC:     "a.fatoum@...gutronix.de" <a.fatoum@...gutronix.de>,
        "Jason@...c4.com" <Jason@...c4.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "zohar@...ux.ibm.com" <zohar@...ux.ibm.com>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "sumit.garg@...aro.org" <sumit.garg@...aro.org>,
        "david@...ma-star.at" <david@...ma-star.at>,
        "michael@...le.cc" <michael@...le.cc>,
        "john.ernberg@...ia.se" <john.ernberg@...ia.se>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "j.luebbe@...gutronix.de" <j.luebbe@...gutronix.de>,
        "ebiggers@...nel.org" <ebiggers@...nel.org>,
        "richard@....at" <richard@....at>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        Sahil Malhotra <sahil.malhotra@....com>,
        Kshitiz Varshney <kshitiz.varshney@....com>,
        Horia Geanta <horia.geanta@....com>,
        Varun Sethi <V.Sethi@....com>
Subject: RE: [EXT] Re: [RFC PATCH HBK: 0/8] HW BOUND KEY as TRUSTED KEY



> -----Original Message-----
> From: Jan Lübbe <jlu@...gutronix.de>
> Sent: Wednesday, September 7, 2022 1:41 PM
> To: Pankaj Gupta <pankaj.gupta@....com>; Jarkko Sakkinen
> <jarkko@...nel.org>
> Cc: a.fatoum@...gutronix.de; Jason@...c4.com; jejb@...ux.ibm.com;
> zohar@...ux.ibm.com; dhowells@...hat.com; sumit.garg@...aro.org;
> david@...ma-star.at; michael@...le.cc; john.ernberg@...ia.se;
> jmorris@...ei.org; serge@...lyn.com; herbert@...dor.apana.org.au;
> davem@...emloft.net; j.luebbe@...gutronix.de; ebiggers@...nel.org;
> richard@....at; keyrings@...r.kernel.org; linux-crypto@...r.kernel.org;
> linux-integrity@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> security-module@...r.kernel.org; Sahil Malhotra
> <sahil.malhotra@....com>; Kshitiz Varshney <kshitiz.varshney@....com>;
> Horia Geanta <horia.geanta@....com>; Varun Sethi <V.Sethi@....com>
> Subject: Re: [EXT] Re: [RFC PATCH HBK: 0/8] HW BOUND KEY as TRUSTED KEY
> 
> Caution: EXT Email
> 
> On Wed, 2022-09-07 at 07:22 +0000, Pankaj Gupta wrote:
> > Even if somehow the key is retrieved from the keyring, the retrieved
> > key would be an encrypted key.
> > This encrypted key can only be decrypted by Hardware, which generated it.
> >
> > Hence, the retrieved key is unusable outside of the hardware.
> 
> NXP's CAAM unit (i.e. on i.MX6) supports several modes of sealed/encrypted
> keys.
> The (un)sealing process uses a key that is normally derived from a per-device
> key in eFUSES. One aspect of these modes is whether the plaintext key
> material is accessible to the kernel or not.
> 
> Ahmad's patch set added support for a mode where the CAAM is used to
> seal plaintext known to the kernel to a "blob" (in CAAM terminology) on
> export to userspace and the reverse on import. This mode allows the kernel
> to use the plaintext for dm-crypt, to encrypt other keyrings and similar.
> 
> The CAAM has another sealing mode, where it will not allow writing of the
> plaintext key to memory. Instead, it is kept in one of the CAAM-internal key
> registers. There, it can be used for cryptographic operations (i.e. AES). This
> way, the plaintext key is protected even from the kernel. The kernel could
> keep a copy of in sealed form, so it can reload the CAAM's key register when
> needed.
> 
> 
> Pankaj, is that the mode you intend to support with this series?
Yes, this is what is called as "black key", in CAAM terminology.
Black key is nothing but a HBK key.
This is what I am trying to achieve with this patch-set.

> 
> Could you describe the high-level use-cases this would be need for,
> compared to the existing mode where plaintext keys are accessible to the
> kernel? In which cases would you use each mode?
> 

High-level Use-case is to ensure runtime security.
By runtime security, I mean, key that is added to keyring after blob-decapsulation, 
- if get  stolen, then being plain key, security can be compromised.
- After this patch-set, if key get stolen, then being HBK(encrypted by H/W), will not be of any use without HW. Security is not   compromised.

> Regards,
> Jan
> --
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