[PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[Jarkko Sakkinen]

There's no reason to encode OID_TPMSealedData at run-time, as it never
changes.

Replace it with the encoded version, which has exactly the same size:

	67 81 05 0A 01 05

Include OBJECT IDENTIFIER (0x06) tag and length as the epilogue so that
the OID can be simply copied to the blob.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v2:
* Not my day I guess. This one has print_hex_dump() taken away.
  Apologies for spamming. The patch is however tested properly
  with run-tests.sh in https://gitlab.com/jarkkojs/linux-tpmdd-test.
---
 include/linux/asn1_encoder.h              |  4 -
 lib/asn1_encoder.c                        | 91 -----------------------
 security/keys/trusted-keys/trusted_tpm2.c |  7 +-
 3 files changed, 4 insertions(+), 98 deletions(-)

diff --git a/include/linux/asn1_encoder.h b/include/linux/asn1_encoder.h
index 08cd0c2ad34f..afeefdfe2525 100644
--- a/include/linux/asn1_encoder.h
+++ b/include/linux/asn1_encoder.h
@@ -8,14 +8,10 @@
 #include <linux/asn1_ber_bytecode.h>
 #include <linux/bug.h>
 
-#define asn1_oid_len(oid) (sizeof(oid)/sizeof(u32))
 unsigned char *
 asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
 		    s64 integer);
 unsigned char *
-asn1_encode_oid(unsigned char *data, const unsigned char *end_data,
-		u32 oid[], int oid_len);
-unsigned char *
 asn1_encode_tag(unsigned char *data, const unsigned char *end_data,
 		u32 tag, const unsigned char *string, int len);
 unsigned char *
diff --git a/lib/asn1_encoder.c b/lib/asn1_encoder.c
index 0fd3c454a468..c0db3cbebe89 100644
--- a/lib/asn1_encoder.c
+++ b/lib/asn1_encoder.c
@@ -85,97 +85,6 @@ asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
 }
 EXPORT_SYMBOL_GPL(asn1_encode_integer);
 
-/* calculate the base 128 digit values setting the top bit of the first octet */
-static int asn1_encode_oid_digit(unsigned char **_data, int *data_len, u32 oid)
-{
-	unsigned char *data = *_data;
-	int start = 7 + 7 + 7 + 7;
-	int ret = 0;
-
-	if (*data_len < 1)
-		return -EINVAL;
-
-	/* quick case */
-	if (oid == 0) {
-		*data++ = 0x80;
-		(*data_len)--;
-		goto out;
-	}
-
-	while (oid >> start == 0)
-		start -= 7;
-
-	while (start > 0 && *data_len > 0) {
-		u8 byte;
-
-		byte = oid >> start;
-		oid = oid - (byte << start);
-		start -= 7;
-		byte |= 0x80;
-		*data++ = byte;
-		(*data_len)--;
-	}
-
-	if (*data_len > 0) {
-		*data++ = oid;
-		(*data_len)--;
-	} else {
-		ret = -EINVAL;
-	}
-
- out:
-	*_data = data;
-	return ret;
-}
-
-/**
- * asn1_encode_oid() - encode an oid to ASN.1
- * @data:	position to begin encoding at
- * @end_data:	end of data pointer, points one beyond last usable byte in @data
- * @oid:	array of oids
- * @oid_len:	length of oid array
- *
- * this encodes an OID up to ASN.1 when presented as an array of OID values
- */
-unsigned char *
-asn1_encode_oid(unsigned char *data, const unsigned char *end_data,
-		u32 oid[], int oid_len)
-{
-	int data_len = end_data - data;
-	unsigned char *d = data + 2;
-	int i, ret;
-
-	if (WARN(oid_len < 2, "OID must have at least two elements"))
-		return ERR_PTR(-EINVAL);
-
-	if (WARN(oid_len > 32, "OID is too large"))
-		return ERR_PTR(-EINVAL);
-
-	if (IS_ERR(data))
-		return data;
-
-
-	/* need at least 3 bytes for tag, length and OID encoding */
-	if (data_len < 3)
-		return ERR_PTR(-EINVAL);
-
-	data[0] = _tag(UNIV, PRIM, OID);
-	*d++ = oid[0] * 40 + oid[1];
-
-	data_len -= 3;
-
-	for (i = 2; i < oid_len; i++) {
-		ret = asn1_encode_oid_digit(&d, &data_len, oid[i]);
-		if (ret < 0)
-			return ERR_PTR(ret);
-	}
-
-	data[1] = d - data - 2;
-
-	return d;
-}
-EXPORT_SYMBOL_GPL(asn1_encode_oid);
-
 /**
  * asn1_encode_length() - encode a length to follow an ASN.1 tag
  * @data: pointer to encode at
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 8b7dd73d94c1..4a2b4ad5a913 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -26,7 +26,8 @@ static struct tpm2_hash tpm2_hash_map[] = {
 	{HASH_ALGO_SM3_256, TPM_ALG_SM3_256},
 };
 
-static u32 tpm2key_oid[] = { 2, 23, 133, 10, 1, 5 };
+/* Encoded OID_TPMSealedData. */
+static u8 OID_TPMSealedData_ASN1[] = {0x06, 0x06, 0x67, 0x81, 0x05, 0x0a, 0x01, 0x05};
 
 static int tpm2_key_encode(struct trusted_key_payload *payload,
 			   struct trusted_key_options *options,
@@ -51,8 +52,8 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
 	if (!scratch)
 		return -ENOMEM;
 
-	work = asn1_encode_oid(work, end_work, tpm2key_oid,
-			       asn1_oid_len(tpm2key_oid));
+	work = memcpy(work, OID_TPMSealedData_ASN1, sizeof(OID_TPMSealedData_ASN1));
+	work += sizeof(OID_TPMSealedData_ASN1);
 
 	if (options->blobauth_len == 0) {
 		unsigned char bool[3], *w = bool;
-- 
2.45.1

Re: [PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[David Howells]

Jarkko Sakkinen <jarkko@kernel.org> wrote:

> There's no reason to encode OID_TPMSealedData at run-time, as it never
> changes.
> 
> Replace it with the encoded version, which has exactly the same size:
> 
> 	67 81 05 0A 01 05
> 
> Include OBJECT IDENTIFIER (0x06) tag and length as the epilogue so that
> the OID can be simply copied to the blob.

This seems reasonable.  We have a limited set of OIDs we can generate
(currently 1).  Better to store the BER-encoded form and copy that in rather
than trying to turn a pretty-printed OID into the BER encoding unless we
absolutely have to.

David

Re: [PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[David Howells]

Jarkko Sakkinen <jarkko@kernel.org> wrote:

> There's no reason to encode OID_TPMSealedData at run-time, as it never
> changes.
> 
> Replace it with the encoded version, which has exactly the same size:
> 
> 	67 81 05 0A 01 05
> 
> Include OBJECT IDENTIFIER (0x06) tag and length as the epilogue so that
> the OID can be simply copied to the blob.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Reviewed-by: David Howells <dhowells@redhat.com>

Re: [PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[Ben Boeckel]

On Thu, May 23, 2024 at 16:23:37 +0300, Jarkko Sakkinen wrote:
> There's no reason to encode OID_TPMSealedData at run-time, as it never
> changes.
> 
> Replace it with the encoded version, which has exactly the same size:
> 
> 	67 81 05 0A 01 05

Is it the same size? It looks considerably smaller to me (6*4 bytes
versus 8 bytes).

> Include OBJECT IDENTIFIER (0x06) tag and length as the epilogue so that
> the OID can be simply copied to the blob.

An "epilogue" occurs at the end, but it seems to be at the beginning
here (that would be a "prologue").

> -static u32 tpm2key_oid[] = { 2, 23, 133, 10, 1, 5 };
> +/* Encoded OID_TPMSealedData. */
> +static u8 OID_TPMSealedData_ASN1[] = {0x06, 0x06, 0x67, 0x81, 0x05, 0x0a, 0x01, 0x05};

I'd say that a comment of what it encodes would be good to have for
context, but the source tree has `OID_TPMSealedData` in a header with
the value in a comment there, so that seems good enough to me.

> as it never changes.

Should it, perhaps be `const` too?

--Ben

Re: [PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[Jarkko Sakkinen]

On Thu May 23, 2024 at 4:41 PM EEST, Ben Boeckel wrote:
> On Thu, May 23, 2024 at 16:23:37 +0300, Jarkko Sakkinen wrote:
> > There's no reason to encode OID_TPMSealedData at run-time, as it never
> > changes.
> > 
> > Replace it with the encoded version, which has exactly the same size:
> > 
> > 	67 81 05 0A 01 05
>
> Is it the same size? It looks considerably smaller to me (6*4 bytes
> versus 8 bytes).

Not in that sense but in practice the old array stored byte values.
Forgot for that reason that it was actually u32 array.

I can change it to "same number of elements".

>
> > Include OBJECT IDENTIFIER (0x06) tag and length as the epilogue so that
> > the OID can be simply copied to the blob.
>
> An "epilogue" occurs at the end, but it seems to be at the beginning
> here (that would be a "prologue").

Yup, typo.

> > -static u32 tpm2key_oid[] = { 2, 23, 133, 10, 1, 5 };
> > +/* Encoded OID_TPMSealedData. */
> > +static u8 OID_TPMSealedData_ASN1[] = {0x06, 0x06, 0x67, 0x81, 0x05, 0x0a, 0x01, 0x05};
>
> I'd say that a comment of what it encodes would be good to have for
> context, but the source tree has `OID_TPMSealedData` in a header with
> the value in a comment there, so that seems good enough to me.

OK. I named it this way to promote generation these from CSV file 
(see my other response to James).


>
> > as it never changes.
>
> Should it, perhaps be `const` too?

Yup.

>
> --Ben

Thanks for the remarks!

BR, Jarkko

Re: [PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[Jarkko Sakkinen]

On Thu May 23, 2024 at 4:36 PM EEST, David Howells wrote:
> Jarkko Sakkinen <jarkko@kernel.org> wrote:
>
> > There's no reason to encode OID_TPMSealedData at run-time, as it never
> > changes.
> > 
> > Replace it with the encoded version, which has exactly the same size:
> > 
> > 	67 81 05 0A 01 05
> > 
> > Include OBJECT IDENTIFIER (0x06) tag and length as the epilogue so that
> > the OID can be simply copied to the blob.
>
> This seems reasonable.  We have a limited set of OIDs we can generate
> (currently 1).  Better to store the BER-encoded form and copy that in rather
> than trying to turn a pretty-printed OID into the BER encoding unless we
> absolutely have to.

Yup, I crafted a plan in response to James about possibility to generate
all from a CSV file (oid_registry.gen.[sh] and oid_registry.h incldues
oid_registry.gen.h for compat). 

No bandwidth to work in it, but happy to review it.

>
> David

BR, Jarkko

Re: [PATCH v2] KEYS: trusted: Use ASN.1 encoded OID

[Jarkko Sakkinen]

On Thu May 23, 2024 at 4:39 PM EEST, David Howells wrote:
> Jarkko Sakkinen <jarkko@kernel.org> wrote:
>
> > There's no reason to encode OID_TPMSealedData at run-time, as it never
> > changes.
> > 
> > Replace it with the encoded version, which has exactly the same size:
> > 
> > 	67 81 05 0A 01 05
> > 
> > Include OBJECT IDENTIFIER (0x06) tag and length as the epilogue so that
> > the OID can be simply copied to the blob.
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
>
> Reviewed-by: David Howells <dhowells@redhat.com>

Thanks!

BR, Jarkko