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From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Richard Weinberger <richard@nod.at>
Cc: "open list, ASYMMETRIC KEYS" <keyrings@vger.kernel.org>,
	david <david@sigma-star.at>, David Howells <dhowells@redhat.com>,
	davem <davem@davemloft.net>, festevam <festevam@gmail.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	James Bottomley <jejb@linux.ibm.com>,
	James Morris <jmorris@namei.org>,
	Jarkko Sakkinen <jarkko@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	linux-integrity <linux-integrity@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	LSM <linux-security-module@vger.kernel.org>,
	Mimi Zohar <zohar@linux.ibm.com>, linux-imx <linux-imx@nxp.com>,
	kernel <kernel@pengutronix.de>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	shawnguo <shawnguo@kernel.org>
Subject: Re: [PATCH 2/3] KEYS: trusted: Introduce support for NXP DCP-based trusted keys
Date: Wed, 21 Jul 2021 19:17:59 +0200	[thread overview]
Message-ID: <5c381015-64dc-039f-8bc2-3109dd3b9bf4@pengutronix.de> (raw)
In-Reply-To: <2032322938.25484.1626259466410.JavaMail.zimbra@nod.at>

Hello Richard,

On 14.07.21 12:44, Richard Weinberger wrote:
> Ahmad,
> 
> ----- Ursprüngliche Mail -----
>> Von: "Ahmad Fatoum" <a.fatoum@pengutronix.de>
> 
> [...]
> 
> Sure, why not? It shows that you will also in future take care of it.

Good point. I did that for v3.

> 
> [...]
> 
>>> +} __packed;
>>> +
>>> +static bool use_otp_key;
>>> +module_param_named(dcp_use_otp_key, use_otp_key, bool, 0);
>>> +MODULE_PARM_DESC(dcp_use_otp_key, "Use OTP instead of UNIQUE key for sealing");
>>
>> Shouldn't these be documented in admin-guide/kernel-parameters.txt as well?
> 
> Yes. Will do.
> 
>>> +static bool skip_zk_test;
>>> +module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
>>> +MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are
>>> zero'ed");
>>
>> Does this need to be configurible? I'd assume this can only happen when using an
>> unfused OTP. In such a case, it's ok to always warn, so you don't need to make
>> this configurible.
> 
> We found such a setting super useful while working with targets where the keys are
> zero'ed for various reasons.
> There are cases where you want to use/test trusted keys even when the master key
> is void. Our detection logic does not only print a warning, it refuses to load
> blobs. So IMHO the config knob makes sense.

Ah, I missed that it refuses to continue in that case.

> 
>>> +
>>> +static unsigned int calc_blob_len(unsigned int payload_len) 
>>> +{
>>> +	return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
>>> +}
>>> +
>>> +static int do_dcp_crypto(u8 *in, u8 *out, bool is_encrypt)
>>
>> I assume in can't be const because the use with sg APIs?
> 
> I'm pretty sure this was the main reason, but I can check again.
> 
>>> +{
>>> +	int res = 0;
>>> +	struct skcipher_request *req = NULL;
>>> +	DECLARE_CRYPTO_WAIT(wait);
>>> +	struct scatterlist src_sg, dst_sg;
>>> +	struct crypto_skcipher *tfm;
>>> +	u8 paes_key[DCP_PAES_KEYSIZE];
>>> +
>>> +	if (!use_otp_key)
>>
>> I'd invert this. Makes code easier to read.
> 
> Ok. :-)
> 
>>> +		paes_key[0] = DCP_PAES_KEY_UNIQUE;
>>> +	else
>>> +		paes_key[0] = DCP_PAES_KEY_OTP;
>>> +
>>> +	tfm = crypto_alloc_skcipher("ecb-paes-dcp", CRYPTO_ALG_INTERNAL,
>>> +				    CRYPTO_ALG_INTERNAL);
>>> +	if (IS_ERR(tfm)) {
>>> +		res = PTR_ERR(tfm);
>>> +		pr_err("Unable to request DCP pAES-ECB cipher: %i\n", res);
>>
>> Can you define pr_fmt above? There's also %pe now that can directly print out an
>> error pointer.
> 
> pr_fmt is not defined on purpose. include/keys/trusted-type.h defines already one
> and I assumed "trusted_key:" is the desired prefix for all kinds of trusted keys.

Ah, all good then. I didn't define it for CAAM either, but forgot why I didn't
along the way. May've been the same reason.

> [...]
> 
>> - payload_len is at offset 33, but MIN_KEY_SIZE == 32 and there are no minimum
>>   size checks. Couldn't you read beyond the buffer this way?
> 
> The key has a minimum size of MIN_KEY_SIZE, but p->blob (being struct trusted_key_payload->blob[MAX_BLOB_SIZE])
> is much larger.
> So the assumption is that a DCP blob will always be smaller than MAX_BLOB_SIZE.
> 
>> - offset 33 is unaligned for payload_len. Please use get_unaligned_le32 here.
> 
> Oh yes. Makes sense!
> 
> [...]
> 
>>
>> jfyi, in the prelude of my CAAM series, I made this the default
>> when .get_random == NULL.
> 
> Right. :-)
> 
> [...]
> 
>>> +	ret = do_dcp_crypto(buf, buf, true);
>>> +	if (ret)
>>> +		goto out;
>>> +
>>> +	if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
>>> +		pr_err("Device neither in secure nor trusted mode!\n");
>>
>> What's the difference between secure and trusted? Can't this test be skipped
>> if use_otp_key == false?
> 
> DCP has many modes of operation. Secure is one level above trusted.
> For the gory details see "Security Reference Manual for the i.MX 6ULL Applications Processor".
> I'm not sure whether all information my manual describes is publicly available so I
> don't dare to copy&paste from it.
> 
> As David and I understood the logic, both OTP and UNIQUE keys can be zero'ed.
> It is also possible that DCP has no support at all for these keys,
> then you'll also get a zero key. That's why we have this check here.

Thanks for the clarification.

Cheers,
Ahmad

> 
> Thanks,
> //richard
> 


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

WARNING: multiple messages have this Message-ID
From: Ahmad Fatoum <a.fatoum@pengutronix.de>
To: Richard Weinberger <richard@nod.at>
Cc: "open list, ASYMMETRIC KEYS" <keyrings@vger.kernel.org>,
	david <david@sigma-star.at>, David Howells <dhowells@redhat.com>,
	davem <davem@davemloft.net>, festevam <festevam@gmail.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	James Bottomley <jejb@linux.ibm.com>,
	James Morris <jmorris@namei.org>,
	Jarkko Sakkinen <jarkko@kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	linux-integrity <linux-integrity@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	LSM <linux-security-module@vger.kernel.org>,
	Mimi Zohar <zohar@linux.ibm.com>, linux-imx <linux-imx@nxp.com>,
	kernel <kernel@pengutronix.de>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	shawnguo <shawnguo@kernel.org>
Subject: Re: [PATCH 2/3] KEYS: trusted: Introduce support for NXP DCP-based trusted keys
Date: Wed, 21 Jul 2021 19:17:59 +0200	[thread overview]
Message-ID: <5c381015-64dc-039f-8bc2-3109dd3b9bf4@pengutronix.de> (raw)
In-Reply-To: <2032322938.25484.1626259466410.JavaMail.zimbra@nod.at>

Hello Richard,

On 14.07.21 12:44, Richard Weinberger wrote:
> Ahmad,
> 
> ----- Ursprüngliche Mail -----
>> Von: "Ahmad Fatoum" <a.fatoum@pengutronix.de>
> 
> [...]
> 
> Sure, why not? It shows that you will also in future take care of it.

Good point. I did that for v3.

> 
> [...]
> 
>>> +} __packed;
>>> +
>>> +static bool use_otp_key;
>>> +module_param_named(dcp_use_otp_key, use_otp_key, bool, 0);
>>> +MODULE_PARM_DESC(dcp_use_otp_key, "Use OTP instead of UNIQUE key for sealing");
>>
>> Shouldn't these be documented in admin-guide/kernel-parameters.txt as well?
> 
> Yes. Will do.
> 
>>> +static bool skip_zk_test;
>>> +module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
>>> +MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are
>>> zero'ed");
>>
>> Does this need to be configurible? I'd assume this can only happen when using an
>> unfused OTP. In such a case, it's ok to always warn, so you don't need to make
>> this configurible.
> 
> We found such a setting super useful while working with targets where the keys are
> zero'ed for various reasons.
> There are cases where you want to use/test trusted keys even when the master key
> is void. Our detection logic does not only print a warning, it refuses to load
> blobs. So IMHO the config knob makes sense.

Ah, I missed that it refuses to continue in that case.

> 
>>> +
>>> +static unsigned int calc_blob_len(unsigned int payload_len) 
>>> +{
>>> +	return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
>>> +}
>>> +
>>> +static int do_dcp_crypto(u8 *in, u8 *out, bool is_encrypt)
>>
>> I assume in can't be const because the use with sg APIs?
> 
> I'm pretty sure this was the main reason, but I can check again.
> 
>>> +{
>>> +	int res = 0;
>>> +	struct skcipher_request *req = NULL;
>>> +	DECLARE_CRYPTO_WAIT(wait);
>>> +	struct scatterlist src_sg, dst_sg;
>>> +	struct crypto_skcipher *tfm;
>>> +	u8 paes_key[DCP_PAES_KEYSIZE];
>>> +
>>> +	if (!use_otp_key)
>>
>> I'd invert this. Makes code easier to read.
> 
> Ok. :-)
> 
>>> +		paes_key[0] = DCP_PAES_KEY_UNIQUE;
>>> +	else
>>> +		paes_key[0] = DCP_PAES_KEY_OTP;
>>> +
>>> +	tfm = crypto_alloc_skcipher("ecb-paes-dcp", CRYPTO_ALG_INTERNAL,
>>> +				    CRYPTO_ALG_INTERNAL);
>>> +	if (IS_ERR(tfm)) {
>>> +		res = PTR_ERR(tfm);
>>> +		pr_err("Unable to request DCP pAES-ECB cipher: %i\n", res);
>>
>> Can you define pr_fmt above? There's also %pe now that can directly print out an
>> error pointer.
> 
> pr_fmt is not defined on purpose. include/keys/trusted-type.h defines already one
> and I assumed "trusted_key:" is the desired prefix for all kinds of trusted keys.

Ah, all good then. I didn't define it for CAAM either, but forgot why I didn't
along the way. May've been the same reason.

> [...]
> 
>> - payload_len is at offset 33, but MIN_KEY_SIZE == 32 and there are no minimum
>>   size checks. Couldn't you read beyond the buffer this way?
> 
> The key has a minimum size of MIN_KEY_SIZE, but p->blob (being struct trusted_key_payload->blob[MAX_BLOB_SIZE])
> is much larger.
> So the assumption is that a DCP blob will always be smaller than MAX_BLOB_SIZE.
> 
>> - offset 33 is unaligned for payload_len. Please use get_unaligned_le32 here.
> 
> Oh yes. Makes sense!
> 
> [...]
> 
>>
>> jfyi, in the prelude of my CAAM series, I made this the default
>> when .get_random == NULL.
> 
> Right. :-)
> 
> [...]
> 
>>> +	ret = do_dcp_crypto(buf, buf, true);
>>> +	if (ret)
>>> +		goto out;
>>> +
>>> +	if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
>>> +		pr_err("Device neither in secure nor trusted mode!\n");
>>
>> What's the difference between secure and trusted? Can't this test be skipped
>> if use_otp_key == false?
> 
> DCP has many modes of operation. Secure is one level above trusted.
> For the gory details see "Security Reference Manual for the i.MX 6ULL Applications Processor".
> I'm not sure whether all information my manual describes is publicly available so I
> don't dare to copy&paste from it.
> 
> As David and I understood the logic, both OTP and UNIQUE keys can be zero'ed.
> It is also possible that DCP has no support at all for these keys,
> then you'll also get a zero key. That's why we have this check here.

Thanks for the clarification.

Cheers,
Ahmad

> 
> Thanks,
> //richard
> 


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-07-21 17:18 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-14 20:16 [PATCH 0/3] DCP as trusted keys backend Richard Weinberger
2021-06-14 20:16 ` Richard Weinberger
2021-06-14 20:16 ` [PATCH 1/3] crypto: mxs-dcp: Add support for hardware provided keys Richard Weinberger
2021-06-14 20:16   ` Richard Weinberger
2021-06-25 12:21   ` Richard Weinberger
2021-06-25 12:21     ` Richard Weinberger
2021-06-25 12:28     ` Herbert Xu
2021-06-25 12:28       ` Herbert Xu
2021-06-25 13:12       ` Richard Weinberger
2021-06-25 13:12         ` Richard Weinberger
2021-07-14  9:24   ` Ahmad Fatoum
2021-07-14  9:24     ` Ahmad Fatoum
2021-07-14 10:39     ` Richard Weinberger
2021-07-14 10:39       ` Richard Weinberger
2021-07-14 11:01       ` Ahmad Fatoum
2021-07-14 11:01         ` Ahmad Fatoum
2021-06-14 20:16 ` [PATCH 2/3] KEYS: trusted: Introduce support for NXP DCP-based trusted keys Richard Weinberger
2021-06-14 20:16   ` Richard Weinberger
2021-07-14  9:29   ` Ahmad Fatoum
2021-07-14  9:29     ` Ahmad Fatoum
2021-07-14 10:44     ` Richard Weinberger
2021-07-14 10:44       ` Richard Weinberger
2021-07-21 17:17       ` Ahmad Fatoum [this message]
2021-07-21 17:17         ` Ahmad Fatoum
2021-06-14 20:16 ` [PATCH 3/3] doc: trusted-encrypted: add DCP as new trust source Richard Weinberger
2021-06-14 20:16   ` Richard Weinberger
2021-07-14  9:32   ` Ahmad Fatoum
2021-07-14  9:32     ` Ahmad Fatoum

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