linux-kernel - Re: [GIT PULL] New TPM driver, hwrng driver and fixes

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Date:	Fri, 27 Jul 2012 19:45:45 -0500
From:	Kent Yoder <shpedoikal@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Kent Yoder <key@...ux.vnet.ibm.com>,
	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	tpmdd-devel@...ts.sourceforge.net,
	Peter Huewe <peter.huewe@...ineon.com>,
	Bryan Freed <bfreed@...omium.org>,
	David Safford <safford@...ux.vnet.ibm.com>
Subject: Re: [GIT PULL] New TPM driver, hwrng driver and fixes

>> +                     /* err can be positive if it came from the TPM itself,
>> +                      * so return a negative value here instead. */
>> +                     err = -EFAULT;
>
> -EFAULT is definitely wrong (that means a bad pointer was passed), you
> can use -EIO instead.
>
> However, I would suggest:
>
>         err = total ? total : -EIO;

 This is fine w/ me...

> ... so you report the number of bytes successfully received if we got
> any.  However, since you *also* do that on the retry line,
>
>> +                     goto out_err;
>> +             }
>> +
>> +             recd = be32_to_cpu(tpm_cmd.params.getrandom_out.rng_data_len);
>> +             memcpy(dest, tpm_cmd.params.getrandom_out.rng_data, recd);
>> +
>> +             dest += recd;
>> +             total += recd;
>> +             num_bytes -= recd;
>> +     } while (retries-- && total < max);
>> +
>> +     err = total;
>
> Should we return something other than 0 if we run out of retries here, too?

  Ugh, I was hoping to avoid this kind of complexity.

> Perhaps we should just do the same "err = total ? total : -EIO;" here
> and the above statement can just turn into a break;.

  Yeah, this seems like the right thing to do.

>> -     ret = my_get_random(hash, SHA1_DIGEST_SIZE);
>> +     ret = tpm_get_random(TPM_ANY_NUM, hash, SHA1_DIGEST_SIZE);
>>       if (ret < 0)
>>               return ret;
>
> You are still not checking the return values correctly!

  Dave, can you weigh in on these individual cases?  In some cases
like capping a pcr I think using uninitialized stack data could be
better than failing...

Kent

> This needs to be something like:
>
>         ret = tpm_get_random(TPM_ANY_NUM, hash, SHA1_DIGEST_SIZE);
>         if (ret != SHA1_DIGEST_SIZE)
>                 return -EIO;    /* Or whatever is appropriate here */
>
>
>         -hpa
> --
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