From: Tyler Hicks <tyhicks@canonical.com>
To: Roberto Sassu <roberto.sassu@huawei.com>
Cc: jarkko.sakkinen@linux.intel.com, jejb@linux.ibm.com,
zohar@linux.ibm.com, jgg@ziepe.ca,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, keyrings@vger.kernel.org,
linux-kernel@vger.kernel.org, crazyt2019+lml@gmail.com,
nayna@linux.vnet.ibm.com, silviu.vlasceanu@huawei.com
Subject: Re: [PATCH v3] KEYS: trusted: allow module init if TPM is inactive or deactivated
Date: Mon, 5 Aug 2019 12:20:14 -0500 [thread overview]
Message-ID: <20190805172014.GE3449@elm> (raw)
In-Reply-To: <20190805164427.17408-1-roberto.sassu@huawei.com>
On 2019-08-05 18:44:27, Roberto Sassu wrote:
> Commit c78719203fc6 ("KEYS: trusted: allow trusted.ko to initialize w/o a
> TPM") allows the trusted module to be loaded even if a TPM is not found, to
> avoid module dependency problems.
>
> However, trusted module initialization can still fail if the TPM is
> inactive or deactivated. tpm_get_random() returns an error.
>
> This patch removes the call to tpm_get_random() and instead extends the PCR
> specified by the user with zeros. The security of this alternative is
> equivalent to the previous one, as either option prevents with a PCR update
> unsealing and misuse of sealed data by a user space process.
>
> Even if a PCR is extended with zeros, instead of random data, it is still
> computationally infeasible to find a value as input for a new PCR extend
> operation, to obtain again the PCR value that would allow unsealing.
>
> Fixes: 240730437deb ("KEYS: trusted: explicitly use tpm_chip structure...")
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
The approach changed a fair bit from v2 to v3 so I'll confirm that my
Reviewed-by still stands.
Also, we have positive test results from an affected user:
https://bugzilla.kernel.org/show_bug.cgi?id=203953#c10
Tyler
> Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
> security/keys/trusted.c | 13 -------------
> 1 file changed, 13 deletions(-)
>
> diff --git a/security/keys/trusted.c b/security/keys/trusted.c
> index 9a94672e7adc..ade699131065 100644
> --- a/security/keys/trusted.c
> +++ b/security/keys/trusted.c
> @@ -1228,24 +1228,11 @@ static int __init trusted_shash_alloc(void)
>
> static int __init init_digests(void)
> {
> - u8 digest[TPM_MAX_DIGEST_SIZE];
> - int ret;
> - int i;
> -
> - ret = tpm_get_random(chip, digest, TPM_MAX_DIGEST_SIZE);
> - if (ret < 0)
> - return ret;
> - if (ret < TPM_MAX_DIGEST_SIZE)
> - return -EFAULT;
> -
> digests = kcalloc(chip->nr_allocated_banks, sizeof(*digests),
> GFP_KERNEL);
> if (!digests)
> return -ENOMEM;
>
> - for (i = 0; i < chip->nr_allocated_banks; i++)
> - memcpy(digests[i].digest, digest, TPM_MAX_DIGEST_SIZE);
> -
> return 0;
> }
>
> --
> 2.17.1
>
next prev parent reply other threads:[~2019-08-05 17:20 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-05 16:44 [PATCH v3] KEYS: trusted: allow module init if TPM is inactive or deactivated Roberto Sassu
2019-08-05 17:20 ` Tyler Hicks [this message]
2019-08-05 22:12 ` Jarkko Sakkinen
2019-08-09 15:50 ` Jarkko Sakkinen
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