| Message ID | 20201129222004.4428-4-James.Bottomley@HansenPartnership.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | TPM 2.0 trusted key rework | expand |
On 11/29/2020 5:20 PM, James Bottomley wrote: > > Note this is both and enhancement and a potential bug fix. The TPM > 2.0 spec requires us to strip leading zeros, meaning empyty > authorization is a zero length HMAC whereas we're currently passing in > 20 bytes of zeros. A lot of TPMs simply accept this as OK, but the > Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this patch > makes the Microsoft TPM emulator work with trusted keys. 1 - To be precise, it strips trailing zeros, but 20 bytes of zero results in an empty buffer either way. " Part 1 19.6.4.3 Authorization Size Convention Trailing octets of zero are to be removed from any string before it is used as an authValue. " 2 - If you have a test case for the MS simulator, post it and I'll give it a try. I did a quick test, power cycle to set platform auth to empty, than create primary with a parent password 20 bytes of zero, and the SW TPM accepted it. This was a password session, not an HMAC session.
On Tue, 2020-12-22 at 18:01 -0500, Ken Goldman wrote: > On 11/29/2020 5:20 PM, James Bottomley wrote: > > Note this is both and enhancement and a potential bug fix. The TPM > > 2.0 spec requires us to strip leading zeros, meaning empyty > > authorization is a zero length HMAC whereas we're currently passing > > in 20 bytes of zeros. A lot of TPMs simply accept this as OK, but > > the Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this > > patch makes the Microsoft TPM emulator work with trusted keys. > > 1 - To be precise, it strips trailing zeros, but 20 bytes of zero > results in an empty buffer either way. > > " > Part 1 19.6.4.3 Authorization Size Convention > > Trailing octets of zero are to be removed from any string before it > is used as an authValue. > " > > > 2 - If you have a test case for the MS simulator, post it and I'll > give it a try. > > I did a quick test, power cycle to set platform auth to empty, than > create primary with a parent password 20 bytes of zero, and the > SW TPM accepted it. > > This was a password session, not an HMAC session. I reported it to Microsoft as soon as I found the problem, so, since this patch set has been languishing for years, I'd hope it would be fixed by now. It is still, however, possible there still exist TPM implementations based on the unfixed Microsoft reference platform. James
On Wed, Dec 23, 2020 at 11:58:17AM -0800, James Bottomley wrote: > On Tue, 2020-12-22 at 18:01 -0500, Ken Goldman wrote: > > On 11/29/2020 5:20 PM, James Bottomley wrote: > > > Note this is both and enhancement and a potential bug fix. The TPM > > > 2.0 spec requires us to strip leading zeros, meaning empyty > > > authorization is a zero length HMAC whereas we're currently passing > > > in 20 bytes of zeros. A lot of TPMs simply accept this as OK, but > > > the Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this > > > patch makes the Microsoft TPM emulator work with trusted keys. > > > > 1 - To be precise, it strips trailing zeros, but 20 bytes of zero > > results in an empty buffer either way. > > > > " > > Part 1 19.6.4.3 Authorization Size Convention > > > > Trailing octets of zero are to be removed from any string before it > > is used as an authValue. > > " > > > > > > 2 - If you have a test case for the MS simulator, post it and I'll > > give it a try. > > > > I did a quick test, power cycle to set platform auth to empty, than > > create primary with a parent password 20 bytes of zero, and the > > SW TPM accepted it. > > > > This was a password session, not an HMAC session. > > I reported it to Microsoft as soon as I found the problem, so, since > this patch set has been languishing for years, I'd hope it would be > fixed by now. It is still, however, possible there still exist TPM > implementations based on the unfixed Microsoft reference platform. > > James One year :-) A bit over but by all practical means... [*] BTW, can you use my kernel org address for v15? [*] https://lore.kernel.org/linux-integrity/1575781600.14069.8.camel@HansenPartnership.com/ /Jarkko
diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h index a94c03a61d8f..b2ed3481c6a0 100644 --- a/include/keys/trusted-type.h +++ b/include/keys/trusted-type.h @@ -30,6 +30,7 @@ struct trusted_key_options { uint16_t keytype; uint32_t keyhandle; unsigned char keyauth[TPM_DIGEST_SIZE]; + uint32_t blobauth_len; unsigned char blobauth[TPM_DIGEST_SIZE]; uint32_t pcrinfo_len; unsigned char pcrinfo[MAX_PCRINFO_SIZE]; diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c index b9fe02e5f84f..eaa2e7ca136e 100644 --- a/security/keys/trusted-keys/trusted_tpm1.c +++ b/security/keys/trusted-keys/trusted_tpm1.c @@ -781,13 +781,33 @@ static int getoptions(char *c, struct trusted_key_payload *pay, return -EINVAL; break; case Opt_blobauth: - if (strlen(args[0].from) != 2 * SHA1_DIGEST_SIZE) - return -EINVAL; - res = hex2bin(opt->blobauth, args[0].from, - SHA1_DIGEST_SIZE); - if (res < 0) - return -EINVAL; + /* + * TPM 1.2 authorizations are sha1 hashes passed in as + * hex strings. TPM 2.0 authorizations are simple + * passwords (although it can take a hash as well) + */ + opt->blobauth_len = strlen(args[0].from); + + if (opt->blobauth_len == 2 * TPM_DIGEST_SIZE) { + res = hex2bin(opt->blobauth, args[0].from, + TPM_DIGEST_SIZE); + if (res < 0) + return -EINVAL; + + opt->blobauth_len = TPM_DIGEST_SIZE; + break; + } + + if (tpm2 && opt->blobauth_len <= sizeof(opt->blobauth)) { + memcpy(opt->blobauth, args[0].from, + opt->blobauth_len); + break; + } + + return -EINVAL; + break; + case Opt_migratable: if (*args[0].from == '0') pay->migratable = 0; diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c index 38bb33333cdf..6c6dd88d7bf6 100644 --- a/security/keys/trusted-keys/trusted_tpm2.c +++ b/security/keys/trusted-keys/trusted_tpm2.c @@ -91,10 +91,12 @@ int tpm2_seal_trusted(struct tpm_chip *chip, TPM_DIGEST_SIZE); /* sensitive */ - tpm_buf_append_u16(&buf, 4 + TPM_DIGEST_SIZE + payload->key_len + 1); + tpm_buf_append_u16(&buf, 4 + options->blobauth_len + payload->key_len + 1); + + tpm_buf_append_u16(&buf, options->blobauth_len); + if (options->blobauth_len) + tpm_buf_append(&buf, options->blobauth, options->blobauth_len); - tpm_buf_append_u16(&buf, TPM_DIGEST_SIZE); - tpm_buf_append(&buf, options->blobauth, TPM_DIGEST_SIZE); tpm_buf_append_u16(&buf, payload->key_len + 1); tpm_buf_append(&buf, payload->key, payload->key_len); tpm_buf_append_u8(&buf, payload->migratable); @@ -258,7 +260,7 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip, NULL /* nonce */, 0, TPM2_SA_CONTINUE_SESSION, options->blobauth /* hmac */, - TPM_DIGEST_SIZE); + options->blobauth_len); rc = tpm_send(chip, buf.data, tpm_buf_length(&buf)); if (rc > 0)
In TPM 1.2 an authorization was a 20 byte number. The spec actually recommended you to hash variable length passwords and use the sha1 hash as the authorization. Because the spec doesn't require this hashing, the current authorization for trusted keys is a 40 digit hex number. For TPM 2.0 the spec allows the passing in of variable length passwords and passphrases directly, so we should allow that in trusted keys for ease of use. Update the 'blobauth' parameter to take this into account, so we can now use plain text passwords for the keys. so before keyctl add trusted kmk "new 32 blobauth=f572d396fae9206628714fb2ce00f72e94f2258fkeyhandle=81000001" @u after we will accept both the old hex sha1 form as well as a new directly supplied password: keyctl add trusted kmk "new 32 blobauth=hello keyhandle=81000001" @u Since a sha1 hex code must be exactly 40 bytes long and a direct password must be 20 or less, we use the length as the discriminator for which form is input. Note this is both and enhancement and a potential bug fix. The TPM 2.0 spec requires us to strip leading zeros, meaning empyty authorization is a zero length HMAC whereas we're currently passing in 20 bytes of zeros. A lot of TPMs simply accept this as OK, but the Microsoft TPM emulator rejects it with TPM_RC_BAD_AUTH, so this patch makes the Microsoft TPM emulator work with trusted keys. Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0 chips") Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> --- v6: change comment, eliminate else clauses and add fixes tag v7: fixes before signoff v12: fix mismerge from v6 to make processing continue after blobauth v14: add tested by Merge with auth fix --- include/keys/trusted-type.h | 1 + security/keys/trusted-keys/trusted_tpm1.c | 32 ++++++++++++++++++----- security/keys/trusted-keys/trusted_tpm2.c | 10 ++++--- 3 files changed, 33 insertions(+), 10 deletions(-)