[PATCH v3 3/3] tpm: Address !chip->auth in tpm_buf_append_hmac_session*()

Jarkko Sakkinen
2024-07-04T08:57:38Z

Unless tpm_chip_bootstrap() was called by the driver, !chip->auth can
cause a null derefence in tpm_buf_hmac_session*(). Thus, address
!chip->auth in tpm_buf_hmac_session*() and remove the fallback
implementation for !TCG_TPM2_HMAC.

Cc: stable@vger.kernel.org # v6.9+
Reported-by: Stefan Berger <stefanb@linux.ibm.com>
Closes: https://lore.kernel.org/linux-integrity/20240617193408.1234365-1-stefanb@linux.ibm.com/
Fixes: 1085b8276bb4 ("tpm: Add the rest of the session HMAC API")
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v3:
* Address:
https://lore.kernel.org/linux-integrity/922603265d61011dbb23f18a04525ae973b83ffd.camel@HansenPartnership.com/
v2:
* Use auth in place of chip->auth.
---
drivers/char/tpm/tpm2-sessions.c | 184 ++++++++++++++++++-------------
include/linux/tpm.h | 68 ++++--------
2 files changed, 128 insertions(+), 124 deletions(-)

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 179bcaac06ce..e0be22b8ae70 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -270,6 +270,108 @@ void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
}
EXPORT_SYMBOL_GPL(tpm_buf_append_name);

+/**
+ * tpm_buf_append_hmac_session() - Append a TPM session element
+ * @chip: the TPM chip structure
+ * @buf: The buffer to be appended
+ * @attributes: The session attributes
+ * @passphrase: The session authority (NULL if none)
+ * @passphrase_len: The length of the session authority (0 if none)
+ *
+ * This fills in a session structure in the TPM command buffer, except
+ * for the HMAC which cannot be computed until the command buffer is
+ * complete. The type of session is controlled by the @attributes,
+ * the main ones of which are TPM2_SA_CONTINUE_SESSION which means the
+ * session won't terminate after tpm_buf_check_hmac_response(),
+ * TPM2_SA_DECRYPT which means this buffers first parameter should be
+ * encrypted with a session key and TPM2_SA_ENCRYPT, which means the
+ * response buffer's first parameter needs to be decrypted (confusing,
+ * but the defines are written from the point of view of the TPM).
+ *
+ * Any session appended by this command must be finalized by calling
+ * tpm_buf_fill_hmac_session() otherwise the HMAC will be incorrect
+ * and the TPM will reject the command.
+ *
+ * As with most tpm_buf operations, success is assumed because failure
+ * will be caused by an incorrect programming model and indicated by a
+ * kernel message.
+ */
+void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
+ u8 attributes, u8 *passphrase,
+ int passphrase_len)
+{
+ u8 __maybe_unused nonce[SHA256_DIGEST_SIZE];
+ struct tpm2_auth __maybe_unused *auth;
+ u32 __maybe_unused len;
+
+ if (!__and(IS_ENABLED(CONFIG_TCG_TPM2_HMAC), chip->auth)) {
+ /* offset tells us where the sessions area begins */
+ int offset = buf->handles * 4 + TPM_HEADER_SIZE;
+ u32 len = 9 + passphrase_len;
+
+ if (tpm_buf_length(buf) != offset) {
+ /* not the first session so update the existing length */
+ len += get_unaligned_be32(&buf->data[offset]);
+ put_unaligned_be32(len, &buf->data[offset]);
+ } else {
+ tpm_buf_append_u32(buf, len);
+ }
+ /* auth handle */
+ tpm_buf_append_u32(buf, TPM2_RS_PW);
+ /* nonce */
+ tpm_buf_append_u16(buf, 0);
+ /* attributes */
+ tpm_buf_append_u8(buf, 0);
+ /* passphrase */
+ tpm_buf_append_u16(buf, passphrase_len);
+ tpm_buf_append(buf, passphrase, passphrase_len);
+ return;
+ }
+
+#ifdef CONFIG_TCG_TPM2_HMAC
+ /*
+ * The Architecture Guide requires us to strip trailing zeros
+ * before computing the HMAC
+ */
+ while (passphrase && passphrase_len > 0 && passphrase[passphrase_len - 1] == '\0')
+ passphrase_len--;
+
+ auth = chip->auth;
+ auth->attrs = attributes;
+ auth->passphrase_len = passphrase_len;
+ if (passphrase_len)
+ memcpy(auth->passphrase, passphrase, passphrase_len);
+
+ if (auth->session != tpm_buf_length(buf)) {
+ /* we're not the first session */
+ len = get_unaligned_be32(&buf->data[auth->session]);
+ if (4 + len + auth->session != tpm_buf_length(buf)) {
+ WARN(1, "session length mismatch, cannot append");
+ return;
+ }
+
+ /* add our new session */
+ len += 9 + 2 * SHA256_DIGEST_SIZE;
+ put_unaligned_be32(len, &buf->data[auth->session]);
+ } else {
+ tpm_buf_append_u32(buf, 9 + 2 * SHA256_DIGEST_SIZE);
+ }
+
+ /* random number for our nonce */
+ get_random_bytes(nonce, sizeof(nonce));
+ memcpy(auth->our_nonce, nonce, sizeof(nonce));
+ tpm_buf_append_u32(buf, auth->handle);
+ /* our new nonce */
+ tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
+ tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
+ tpm_buf_append_u8(buf, auth->attrs);
+ /* and put a placeholder for the hmac */
+ tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
+ tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
+#endif /* CONFIG_TCG_TPM2_HMAC */
+}
+EXPORT_SYMBOL_GPL(tpm_buf_append_hmac_session);
+
#ifdef CONFIG_TCG_TPM2_HMAC

static int tpm2_create_primary(struct tpm_chip *chip, u32 hierarchy,
@@ -455,82 +557,6 @@ static void tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip)
crypto_free_kpp(kpp);
}

-/**
- * tpm_buf_append_hmac_session() - Append a TPM session element
- * @chip: the TPM chip structure
- * @buf: The buffer to be appended
- * @attributes: The session attributes
- * @passphrase: The session authority (NULL if none)
- * @passphrase_len: The length of the session authority (0 if none)
- *
- * This fills in a session structure in the TPM command buffer, except
- * for the HMAC which cannot be computed until the command buffer is
- * complete. The type of session is controlled by the @attributes,
- * the main ones of which are TPM2_SA_CONTINUE_SESSION which means the
- * session won't terminate after tpm_buf_check_hmac_response(),
- * TPM2_SA_DECRYPT which means this buffers first parameter should be
- * encrypted with a session key and TPM2_SA_ENCRYPT, which means the
- * response buffer's first parameter needs to be decrypted (confusing,
- * but the defines are written from the point of view of the TPM).
- *
- * Any session appended by this command must be finalized by calling
- * tpm_buf_fill_hmac_session() otherwise the HMAC will be incorrect
- * and the TPM will reject the command.
- *
- * As with most tpm_buf operations, success is assumed because failure
- * will be caused by an incorrect programming model and indicated by a
- * kernel message.
- */
-void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
- u8 attributes, u8 *passphrase,
- int passphrase_len)
-{
- u8 nonce[SHA256_DIGEST_SIZE];
- u32 len;
- struct tpm2_auth *auth = chip->auth;
-
- /*
- * The Architecture Guide requires us to strip trailing zeros
- * before computing the HMAC
- */
- while (passphrase && passphrase_len > 0
- && passphrase[passphrase_len - 1] == '\0')
- passphrase_len--;
-
- auth->attrs = attributes;
- auth->passphrase_len = passphrase_len;
- if (passphrase_len)
- memcpy(auth->passphrase, passphrase, passphrase_len);
-
- if (auth->session != tpm_buf_length(buf)) {
- /* we're not the first session */
- len = get_unaligned_be32(&buf->data[auth->session]);
- if (4 + len + auth->session != tpm_buf_length(buf)) {
- WARN(1, "session length mismatch, cannot append");
- return;
- }
-
- /* add our new session */
- len += 9 + 2 * SHA256_DIGEST_SIZE;
- put_unaligned_be32(len, &buf->data[auth->session]);
- } else {
- tpm_buf_append_u32(buf, 9 + 2 * SHA256_DIGEST_SIZE);
- }
-
- /* random number for our nonce */
- get_random_bytes(nonce, sizeof(nonce));
- memcpy(auth->our_nonce, nonce, sizeof(nonce));
- tpm_buf_append_u32(buf, auth->handle);
- /* our new nonce */
- tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
- tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
- tpm_buf_append_u8(buf, auth->attrs);
- /* and put a placeholder for the hmac */
- tpm_buf_append_u16(buf, SHA256_DIGEST_SIZE);
- tpm_buf_append(buf, nonce, SHA256_DIGEST_SIZE);
-}
-EXPORT_SYMBOL(tpm_buf_append_hmac_session);
-
/**
* tpm_buf_fill_hmac_session() - finalize the session HMAC
* @chip: the TPM chip structure
@@ -561,6 +587,9 @@ void tpm_buf_fill_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf)
u8 cphash[SHA256_DIGEST_SIZE];
struct sha256_state sctx;

+ if (!auth)
+ return;
+
/* save the command code in BE format */
auth->ordinal = head->ordinal;

@@ -719,6 +748,9 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
u32 cc = be32_to_cpu(auth->ordinal);
int parm_len, len, i, handles;

+ if (!auth)
+ return rc;
+
if (auth->session >= TPM_HEADER_SIZE) {
WARN(1, "tpm session not filled correctly\n");
goto out;
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index d9a6991b247d..e47f5d65935e 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -493,10 +493,6 @@ static inline void tpm_buf_append_empty_auth(struct tpm_buf *buf, u32 handle)

void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
u32 handle, u8 *name);
-
-#ifdef CONFIG_TCG_TPM2_HMAC
-
-int tpm2_start_auth_session(struct tpm_chip *chip);
void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
u8 attributes, u8 *passphrase,
int passphraselen);
@@ -506,9 +502,27 @@ static inline void tpm_buf_append_hmac_session_opt(struct tpm_chip *chip,
u8 *passphrase,
int passphraselen)
{
- tpm_buf_append_hmac_session(chip, buf, attributes, passphrase,
- passphraselen);
+ struct tpm_header *head;
+ int offset;
+
+ if (__and(IS_ENABLED(CONFIG_TCG_TPM2_HMAC), chip->auth)) {
+ tpm_buf_append_hmac_session(chip, buf, attributes, passphrase, passphraselen);
+ } else {
+ offset = buf->handles * 4 + TPM_HEADER_SIZE;
+ head = (struct tpm_header *)buf->data;
+
+ /*
+ * If the only sessions are optional, the command tag must change to
+ * TPM2_ST_NO_SESSIONS.
+ */
+ if (tpm_buf_length(buf) == offset)
+ head->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
+ }
}
+
+#ifdef CONFIG_TCG_TPM2_HMAC
+
+int tpm2_start_auth_session(struct tpm_chip *chip);
void tpm_buf_fill_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf);
int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
int rc);
@@ -523,48 +537,6 @@ static inline int tpm2_start_auth_session(struct tpm_chip *chip)
static inline void tpm2_end_auth_session(struct tpm_chip *chip)
{
}
-static inline void tpm_buf_append_hmac_session(struct tpm_chip *chip,
- struct tpm_buf *buf,
- u8 attributes, u8 *passphrase,
- int passphraselen)
-{
- /* offset tells us where the sessions area begins */
- int offset = buf->handles * 4 + TPM_HEADER_SIZE;
- u32 len = 9 + passphraselen;
-
- if (tpm_buf_length(buf) != offset) {
- /* not the first session so update the existing length */
- len += get_unaligned_be32(&buf->data[offset]);
- put_unaligned_be32(len, &buf->data[offset]);
- } else {
- tpm_buf_append_u32(buf, len);
- }
- /* auth handle */
- tpm_buf_append_u32(buf, TPM2_RS_PW);
- /* nonce */
- tpm_buf_append_u16(buf, 0);
- /* attributes */
- tpm_buf_append_u8(buf, 0);
- /* passphrase */
- tpm_buf_append_u16(buf, passphraselen);
- tpm_buf_append(buf, passphrase, passphraselen);
-}
-static inline void tpm_buf_append_hmac_session_opt(struct tpm_chip *chip,
- struct tpm_buf *buf,
- u8 attributes,
- u8 *passphrase,
- int passphraselen)
-{
- int offset = buf->handles * 4 + TPM_HEADER_SIZE;
- struct tpm_header *head = (struct tpm_header *) buf->data;
-
- /*
- * if the only sessions are optional, the command tag
- * must change to TPM2_ST_NO_SESSIONS
- */
- if (tpm_buf_length(buf) == offset)
- head->tag = cpu_to_be16(TPM2_ST_NO_SESSIONS);
-}
static inline void tpm_buf_fill_hmac_session(struct tpm_chip *chip,
struct tpm_buf *buf)
{
--
2.45.2