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From: Mimi Zohar <zohar@linux.ibm.com>
To: James Bottomley <James.Bottomley@HansenPartnership.com>,
	Jerry Snitselaar <jsnitsel@redhat.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	David Safford <david.safford@ge.com>,
	linux-integrity@vger.kernel.org, stable@vger.kernel.org,
	David Howells <dhowells@redhat.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>,
	"open list:ASYMMETRIC KEYS" <keyrings@vger.kernel.org>,
	"open list:CRYPTO API" <linux-crypto@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()
Date: Sat, 05 Oct 2019 20:38:53 -0400	[thread overview]
Message-ID: <1570322333.5046.145.camel@linux.ibm.com> (raw)
In-Reply-To: <1570227068.17537.4.camel@HansenPartnership.com>

On Fri, 2019-10-04 at 15:11 -0700, James Bottomley wrote:

> +
> +/**
> + * tpm_get_random() - get random bytes influenced by the TPM's RNG
> + * @chip:	a &struct tpm_chip instance, %NULL for the default chip
> + * @out:	destination buffer for the random bytes
> + * @max:	the max number of bytes to write to @out
> + *
> + * Uses the TPM as a source of input to the kernel random number
> + * generator and then takes @max bytes directly from the kernel.  In
> + * the worst (no other entropy) case, this will return the pure TPM
> + * random number, but if the kernel RNG has any entropy at all it will
> + * return a mixed entropy output which doesn't rely on a single
> + * source.
> + *
> + * Return: number of random bytes read or a negative error value.
> + */
> +int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max)
> +{
> +	int rc;
> +
> +	rc = __tpm_get_random(chip, out, max);
> +	if (rc <= 0)
> +		return rc;
> +	/*
> +	 * assume the TPM produces pure randomness, so the amount of
> +	 * entropy is the number of bits returned
> +	 */
> +	add_hwgenerator_randomness(out, rc, rc * 8);
> +	get_random_bytes(out, rc);

Using the TPM as a source of input to the kernel random number
generator is fine, but please don't change the meaning of trusted
keys.  The trusted-encrypted keys documentation clearly states
"Trusted Keys use a TPM both to generate and to seal the keys."

If you really want to use a different random number source instead of
the TPM, then define a new trusted key option (eg. rng=kernel), with
the default being the TPM.

Mimi


> +
> +	return rc;
> +}
>  EXPORT_SYMBOL_GPL(tpm_get_random);


  reply	other threads:[~2019-10-06  0:39 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-26 17:16 Jarkko Sakkinen
2019-09-28 18:05 ` Jerry Snitselaar
2019-10-01 20:54   ` Jarkko Sakkinen
2019-10-02 14:00 ` Mimi Zohar
2019-10-03 11:41   ` Jarkko Sakkinen
2019-10-03 11:43     ` Jarkko Sakkinen
2019-10-03 13:02     ` Mimi Zohar
2019-10-03 17:58       ` Jarkko Sakkinen
2019-10-03 18:53         ` Mimi Zohar
2019-10-03 21:51           ` Jarkko Sakkinen
2019-10-03 21:57             ` Jarkko Sakkinen
2019-10-03 22:08               ` Mimi Zohar
2019-10-03 23:59                 ` James Bottomley
2019-10-04 18:22                   ` Jarkko Sakkinen
2019-10-04 18:24                     ` James Bottomley
2019-10-04 18:33                       ` Jerry Snitselaar
2019-10-04 18:42                         ` James Bottomley
2019-10-04 20:07                           ` Jerry Snitselaar
2019-10-04 20:11                             ` Jerry Snitselaar
2019-10-04 22:11                               ` James Bottomley
2019-10-06  0:38                                 ` Mimi Zohar [this message]
2019-10-06 23:52                                   ` Jarkko Sakkinen
2019-10-07 18:08                                     ` Mimi Zohar
2019-10-04 18:20                 ` Jarkko Sakkinen
2019-10-03 22:10               ` Jarkko Sakkinen
2019-10-04 13:26           ` Safford, David (GE Global Research, US)
2019-10-04 18:27             ` Jarkko Sakkinen
2019-10-04 18:30               ` Jarkko Sakkinen
2019-10-04 19:56               ` Safford, David (GE Global Research, US)
2019-10-07  0:05                 ` Jarkko Sakkinen
2019-10-07 22:13                   ` Ken Goldman
2019-10-08 23:49                     ` Jarkko Sakkinen
2019-10-08 23:53                       ` Jarkko Sakkinen
2019-10-09  7:10                         ` Pascal Van Leeuwen
2019-10-09  7:33                         ` Jarkko Sakkinen
2019-10-09  7:41                           ` Jarkko Sakkinen
2019-10-09  8:09                             ` Pascal Van Leeuwen
2019-10-14 19:11                               ` Jarkko Sakkinen
2019-10-09  8:02                           ` Pascal Van Leeuwen
2019-10-09 12:11                         ` Safford, David (GE Global Research, US)
2019-10-14 19:00                           ` Jarkko Sakkinen
2019-10-14 19:29                             ` Jarkko Sakkinen
2019-10-14 19:29                             ` James Bottomley
2019-10-16 11:00                               ` Jarkko Sakkinen
2019-10-16 12:34                                 ` James Bottomley
2019-10-16 16:25                                   ` Jarkko Sakkinen
2019-10-16 19:10                                     ` James Bottomley
2019-10-17 12:52                                       ` Sumit Garg
2019-10-17 12:58                                         ` James Bottomley
2019-10-17 18:04                                       ` Jarkko Sakkinen
2019-10-21 11:39                                         ` Jarkko Sakkinen
2019-10-29  8:42                                           ` Jarkko Sakkinen
2019-10-29 14:58                                             ` James Bottomley
2019-10-31 21:03                                               ` Jarkko Sakkinen
2019-10-18  7:32                                   ` Janne Karhunen
2019-10-03 18:02       ` Jarkko Sakkinen
2019-10-03 18:15         ` Jarkko Sakkinen
2019-10-07 10:33     ` Janne Karhunen

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