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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 1/3] crypto: mxs-dcp: Add support for hardware provided keys
Date: Wed, 14 Jul 2021 13:01:11 +0200	[thread overview]
Message-ID: <efa704fa-7817-7654-7664-447fa56e5ab2@pengutronix.de> (raw)
In-Reply-To: <1409091619.25467.1626259183269.JavaMail.zimbra@nod.at>

Hi,

On 14.07.21 12:39, Richard Weinberger wrote:
> Ahmad,
> 
> ----- Ursprüngliche Mail -----
>> Von: "Ahmad Fatoum" <a.fatoum@pengutronix.de>
>> Let's trade reviews to get the ball rolling?
> 
> Sounds like a fair deal. :-)

:)

> [...]
> 
>>> --- a/drivers/crypto/mxs-dcp.c
>>> +++ b/drivers/crypto/mxs-dcp.c
>>> @@ -15,6 +15,7 @@
>>>  #include <linux/platform_device.h>
>>>  #include <linux/stmp_device.h>
>>>  #include <linux/clk.h>
>>> +#include <linux/mxs-dcp.h>
>>
>> The CAAM specific headers are in <soc/fsl/*.h>.
>> Should this be done likewise here as well?
> 
> I have no preferences. If soc/fsl/ is the way to go, fine by me.

I think it's the more appropriate place, but if the maintainers
are fine with <linux/mxs-dcp.h>, I don't mind.

> 
> [...]
> 
>>> @@ -219,15 +224,18 @@ static int mxs_dcp_run_aes(struct dcp_async_ctx *actx,
>>>  	struct dcp *sdcp = global_sdcp;
>>>  	struct dcp_dma_desc *desc = &sdcp->coh->desc[actx->chan];
>>>  	struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
>>> +	dma_addr_t src_phys, dst_phys, key_phys = {0};
>>
>> Why = {0}; ? dma_addr_t is a scalar type and the value is always
>> written here before access.
> 
> Initializing a scalar with {} is allowed in C, the braces are optional.
> I like the braces because it works even when the underlaying type changes.
> But that's just a matter of taste.
> 
> key_phys is initialized because it triggered a false positive gcc warning
> on one of my targets. Let me re-run again to be sure, the code saw a lot of
> refactoring since that.
>  
> [...]
>   
>>> +static int mxs_dcp_aes_setrefkey(struct crypto_skcipher *tfm, const u8 *key,
>>> +				 unsigned int len)
>>> +{
>>> +	struct dcp_async_ctx *actx = crypto_skcipher_ctx(tfm);
>>> +	int ret = -EINVAL;
>>> +
>>> +	if (len != DCP_PAES_KEYSIZE)
>>> +		goto out;
>>
>> Nitpick: there is no cleanup, so why not return -EINVAL here
>> and unconditionally return 0 below?
> 
> What is the benefit?

Similar to why you wouldn't write: 

  if (len == DCP_PAES_KEYSIZE) { 
  	/* longer code block */
  }

  return ret;

Code is easier to scan through with early-exits.

> Usually I try to use goto to have a single exit point of a function
> but I don't have a strong preference...

It's just a nitpick. I am fine with it either way.

>>> +
>>> +	actx->key_len = len;
>>> +	actx->refkey = true;
>>> +
>>> +	switch (key[0]) {
>>> +	case DCP_PAES_KEY_SLOT0:
>>> +	case DCP_PAES_KEY_SLOT1:
>>> +	case DCP_PAES_KEY_SLOT2:
>>> +	case DCP_PAES_KEY_SLOT3:
>>> +	case DCP_PAES_KEY_UNIQUE:
>>> +	case DCP_PAES_KEY_OTP:
>>> +		memcpy(actx->key, key, len);
>>> +		ret = 0;
>>> +	}
>>
>> In the error case you return -EINVAL below, but you still write
>> into actx. Is that intentional?
> 
> You mean acts->key_len and actk->refkey?
> Is this a problem?

It's easier to reason about code when it doesn't leave objects
it operates on in invalid states on failure. Changing key_len,
but leaving actx->key uninitialized is surprising IMO.

I can't judge whether this is a problem in practice, but less
surprises are a worthwhile goal.

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 1/3] crypto: mxs-dcp: Add support for hardware provided keys
Date: Wed, 14 Jul 2021 13:01:11 +0200	[thread overview]
Message-ID: <efa704fa-7817-7654-7664-447fa56e5ab2@pengutronix.de> (raw)
In-Reply-To: <1409091619.25467.1626259183269.JavaMail.zimbra@nod.at>

Hi,

On 14.07.21 12:39, Richard Weinberger wrote:
> Ahmad,
> 
> ----- Ursprüngliche Mail -----
>> Von: "Ahmad Fatoum" <a.fatoum@pengutronix.de>
>> Let's trade reviews to get the ball rolling?
> 
> Sounds like a fair deal. :-)

:)

> [...]
> 
>>> --- a/drivers/crypto/mxs-dcp.c
>>> +++ b/drivers/crypto/mxs-dcp.c
>>> @@ -15,6 +15,7 @@
>>>  #include <linux/platform_device.h>
>>>  #include <linux/stmp_device.h>
>>>  #include <linux/clk.h>
>>> +#include <linux/mxs-dcp.h>
>>
>> The CAAM specific headers are in <soc/fsl/*.h>.
>> Should this be done likewise here as well?
> 
> I have no preferences. If soc/fsl/ is the way to go, fine by me.

I think it's the more appropriate place, but if the maintainers
are fine with <linux/mxs-dcp.h>, I don't mind.

> 
> [...]
> 
>>> @@ -219,15 +224,18 @@ static int mxs_dcp_run_aes(struct dcp_async_ctx *actx,
>>>  	struct dcp *sdcp = global_sdcp;
>>>  	struct dcp_dma_desc *desc = &sdcp->coh->desc[actx->chan];
>>>  	struct dcp_aes_req_ctx *rctx = skcipher_request_ctx(req);
>>> +	dma_addr_t src_phys, dst_phys, key_phys = {0};
>>
>> Why = {0}; ? dma_addr_t is a scalar type and the value is always
>> written here before access.
> 
> Initializing a scalar with {} is allowed in C, the braces are optional.
> I like the braces because it works even when the underlaying type changes.
> But that's just a matter of taste.
> 
> key_phys is initialized because it triggered a false positive gcc warning
> on one of my targets. Let me re-run again to be sure, the code saw a lot of
> refactoring since that.
>  
> [...]
>   
>>> +static int mxs_dcp_aes_setrefkey(struct crypto_skcipher *tfm, const u8 *key,
>>> +				 unsigned int len)
>>> +{
>>> +	struct dcp_async_ctx *actx = crypto_skcipher_ctx(tfm);
>>> +	int ret = -EINVAL;
>>> +
>>> +	if (len != DCP_PAES_KEYSIZE)
>>> +		goto out;
>>
>> Nitpick: there is no cleanup, so why not return -EINVAL here
>> and unconditionally return 0 below?
> 
> What is the benefit?

Similar to why you wouldn't write: 

  if (len == DCP_PAES_KEYSIZE) { 
  	/* longer code block */
  }

  return ret;

Code is easier to scan through with early-exits.

> Usually I try to use goto to have a single exit point of a function
> but I don't have a strong preference...

It's just a nitpick. I am fine with it either way.

>>> +
>>> +	actx->key_len = len;
>>> +	actx->refkey = true;
>>> +
>>> +	switch (key[0]) {
>>> +	case DCP_PAES_KEY_SLOT0:
>>> +	case DCP_PAES_KEY_SLOT1:
>>> +	case DCP_PAES_KEY_SLOT2:
>>> +	case DCP_PAES_KEY_SLOT3:
>>> +	case DCP_PAES_KEY_UNIQUE:
>>> +	case DCP_PAES_KEY_OTP:
>>> +		memcpy(actx->key, key, len);
>>> +		ret = 0;
>>> +	}
>>
>> In the error case you return -EINVAL below, but you still write
>> into actx. Is that intentional?
> 
> You mean acts->key_len and actk->refkey?
> Is this a problem?

It's easier to reason about code when it doesn't leave objects
it operates on in invalid states on failure. Changing key_len,
but leaving actx->key uninitialized is surprising IMO.

I can't judge whether this is a problem in practice, but less
surprises are a worthwhile goal.

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:[~2021-07-14 11:01 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 [this message]
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
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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