[PATCH v4 3/7] tpm2: add hmac checks to tpm2_pcr_extend()

[James Bottomley]

We use tpm2_pcr_extend() in trusted keys to extend a PCR to prevent a
key from being re-loaded until the next reboot.  To use this
functionality securely, that extend must be protected by a session
hmac.

Signed-off-by: James Bottomley <james.bottom...@hansenpartnership.com>

---

v3: add error handling to sessions
---
 drivers/char/tpm/tpm2-cmd.c | 33 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index a17e5c573c4e..332b34b347f1 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -209,13 +209,6 @@ int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u8 
*res_buf)
        return rc;
 }
 
-struct tpm2_null_auth_area {
-       __be32  handle;
-       __be16  nonce_size;
-       u8  attributes;
-       __be16  auth_size;
-} __packed;
-
 /**
  * tpm2_pcr_extend() - extend a PCR value
  *
@@ -230,7 +223,7 @@ int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, u32 
count,
                    struct tpm2_digest *digests)
 {
        struct tpm_buf buf;
-       struct tpm2_null_auth_area auth_area;
+       struct tpm2_auth *auth;
        int rc;
        int i;
        int j;
@@ -238,20 +231,19 @@ int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, 
u32 count,
        if (count > ARRAY_SIZE(chip->active_banks))
                return -EINVAL;
 
-       rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND);
+       rc = tpm2_start_auth_session(chip, &auth);
        if (rc)
                return rc;
 
-       tpm_buf_append_u32(&buf, pcr_idx);
+       rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND);
+       if (rc) {
+               tpm2_end_auth_session(auth);
+               return rc;
+       }
 
-       auth_area.handle = cpu_to_be32(TPM2_RS_PW);
-       auth_area.nonce_size = 0;
-       auth_area.attributes = 0;
-       auth_area.auth_size = 0;
+       tpm_buf_append_name(&buf, auth, pcr_idx, NULL);
+       tpm_buf_append_hmac_session(&buf, auth, 0, NULL, 0);
 
-       tpm_buf_append_u32(&buf, sizeof(struct tpm2_null_auth_area));
-       tpm_buf_append(&buf, (const unsigned char *)&auth_area,
-                      sizeof(auth_area));
        tpm_buf_append_u32(&buf, count);
 
        for (i = 0; i < count; i++) {
@@ -264,9 +256,10 @@ int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, 
u32 count,
                               hash_digest_size[tpm2_hash_map[j].crypto_id]);
                }
        }
-
-       rc = tpm_transmit_cmd(chip, NULL, buf.data, PAGE_SIZE, 0, 0,
-                             "attempting extend a PCR value");
+       tpm_buf_fill_hmac_session(&buf, auth);
+       rc = tpm_transmit_cmd(chip, &chip->kernel_space, buf.data, PAGE_SIZE,
+                             0, 0, "attempting extend a PCR value");
+       rc = tpm_buf_check_hmac_response(&buf, auth, rc);
 
        tpm_buf_destroy(&buf);
 
-- 
2.16.4