[PATCH v3] KEYS: trusted: Use ASN.1 encoded OID

Jarkko Sakkinen
2024-05-23T14:21:10Z

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

Replace it with an encoded u8-array, which has the same number of
elements:

67 81 05 0A 01 05

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

06 06 67 81 05 0A 01 05

Since this in stationary place in the buffer it is guaranteed to always
fit and not further checks are required.

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v3:
* Addressed Ben's suggestions:
https://lore.kernel.org/linux-integrity/Zk9Hb-whVYvJrfLY@farprobe/
* Added David's R-b, as the only change in code was to add const
to the declaration.
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 | 6 +-
3 files changed, 3 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..d478096cb5c1 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -26,7 +26,7 @@ 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 };
+static const 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 +51,8 @@ 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