[v6,3/6] security: keys: trusted: fix TPM2 authorizations
diff mbox series

Message ID 20200302122759.5204-4-James.Bottomley@HansenPartnership.com
State New
Headers show
Series
  • TPM 2.0 trusted keys with attached policy
Related show

Commit Message

James Bottomley March 2, 2020, 12:27 p.m. UTC
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=f572d396fae9206628714fb2ce00f72e94f2258f"

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"

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.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0 chips")

---

v6: change comment, eliminate else clauses and add fixes tag
---
 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(-)

Comments

Jarkko Sakkinen March 3, 2020, 7:33 p.m. UTC | #1
On Mon, Mar 02, 2020 at 07:27:56AM -0500, James Bottomley wrote:
> 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=f572d396fae9206628714fb2ce00f72e94f2258f"
> 
> 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"
> 
> 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.

The commit message does not mention it but there limitation that you
cannot have this as a *password*:

  f572d396fae9206628714fb2ce00f72e94f2258f

The commit message should explicitly state this.

> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0 chips")

Fixes should be before SOB.

/Jarkko
James Bottomley March 3, 2020, 8:39 p.m. UTC | #2
On Tue, 2020-03-03 at 21:33 +0200, Jarkko Sakkinen wrote:
> On Mon, Mar 02, 2020 at 07:27:56AM -0500, James Bottomley wrote:
> > 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=f572d396fae9206628714fb2ce00f72e94f2258f"
> > 
> > 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"
> > 
> > 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.
> 
> The commit message does not mention it but there limitation that you
> cannot have this as a *password*:
> 
>   f572d396fae9206628714fb2ce00f72e94f2258f
> 
> The commit message should explicitly state this.

Well, that's impossible anyway: the password can be at most
TPM_DIGEST_SIZE characters and the above is twice that, so the
discriminator is fairly simple: if the string size is less than or
equal to TPM_DIGEST_SIZE, then it's a plain password, if it's exactly
2xTPM_DIGEST_SIZE it must be a hex value and if it's anything else,
it's illegal.  I thought the sentence

   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.

Was the explanation for this, but I can update it.

> > Signed-off-by: James Bottomley
> > <James.Bottomley@HansenPartnership.com>
> > Fixes: 0fe5480303a1 ("keys, trusted: seal/unseal with TPM 2.0
> > chips")
> 
> Fixes should be before SOB.

OK, I'll reverse them.

James
Jarkko Sakkinen March 3, 2020, 9:32 p.m. UTC | #3
On Tue, Mar 03, 2020 at 03:39:08PM -0500, James Bottomley wrote:
> On Tue, 2020-03-03 at 21:33 +0200, Jarkko Sakkinen wrote:
> > On Mon, Mar 02, 2020 at 07:27:56AM -0500, James Bottomley wrote:
> > > 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=f572d396fae9206628714fb2ce00f72e94f2258f"
> > > 
> > > 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"
> > > 
> > > 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.
> > 
> > The commit message does not mention it but there limitation that you
> > cannot have this as a *password*:
> > 
> >   f572d396fae9206628714fb2ce00f72e94f2258f
> > 
> > The commit message should explicitly state this.
> 
> Well, that's impossible anyway: the password can be at most
> TPM_DIGEST_SIZE characters and the above is twice that, so the
> discriminator is fairly simple: if the string size is less than or
> equal to TPM_DIGEST_SIZE, then it's a plain password, if it's exactly
> 2xTPM_DIGEST_SIZE it must be a hex value and if it's anything else,
> it's illegal.  I thought the sentence
> 
>    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.
> 
> Was the explanation for this, but I can update it.

Thanks! No need to update. I missed that part somehow.

/Jarkko

Patch
diff mbox series

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 d2c5ec1e040b..add9f071d818 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;
+				return 0;
+			}
+
+			if (tpm2 && opt->blobauth_len <= sizeof(opt->blobauth)) {
+				memcpy(opt->blobauth, args[0].from,
+				       opt->blobauth_len);
+				return 0;
+			}
+
+			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 08ec7f48f01d..b4a5058107c2 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)