| Message ID | 20190805164427.17408-1-roberto.sassu@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] KEYS: trusted: allow module init if TPM is inactive or deactivated | expand |
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 >
On Mon, Aug 05, 2019 at 06:44:27PM +0200, 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> > Suggested-by: Mimi Zohar <zohar@linux.ibm.com> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> /Jarkko
On Mon, Aug 05, 2019 at 06:44:27PM +0200, 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> > Suggested-by: Mimi Zohar <zohar@linux.ibm.com> OK so this has been now applied. I'm going to do a PR over the weekend, which means that the fix will land to 5.3. /Jarkko
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; }
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> Suggested-by: Mimi Zohar <zohar@linux.ibm.com> --- security/keys/trusted.c | 13 ------------- 1 file changed, 13 deletions(-)