tpm: Opt-in in disable PCR integrity protection

The initial HMAC session feature added TPM bus encryption and/or integrity
protection to various in-kernel TPM operations. This can cause performance
bottlenecks with IMA, as it heavily utilizes PCR extend operations.

In order to mitigate this performance issue, introduce a kernel
command-line parameter to the TPM driver for disabling the integrity
protection for PCR extend operations (i.e. TPM2_PCR_Extend).

Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Link: https://lore.kernel.org/linux-integrity/20241015193916.59964-1-zohar@linux.ibm.com/
Fixes: 6519fea6fd37 ("tpm: add hmac checks to tpm2_pcr_extend()")
Tested-by: Mimi Zohar <zohar@linux.ibm.com>
Co-developed-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1666576acc0eba69389ff623aeca286ff550c5b4..d401577b5a6ace87d250d9b1cc200691c6a0ed4e 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6727,6 +6727,15 @@
        torture.verbose_sleep_duration= [KNL]
                        Duration of each verbose-printk() sleep in jiffies.
 
+       tpm.disable_pcr_integrity= [HW,TPM]
+                       Do not protect PCR registers from unintended physical
+                       access, or interposers in the bus by the means of
+                       having an integrity protected session wrapped around
+                       TPM2_PCR_Extend command. Consider this in a situation
+                       where TPM is heavily utilized by IMA, thus protection
+                       causing a major performance hit, and the space where
+                       machines are deployed is by other means guarded.
+
        tpm_suspend_pcr=[HW,TPM]
                        Format: integer pcr id
                        Specify that at suspend time, the tpm driver

diff --git a/drivers/char/tpm/tpm-buf.c b/drivers/char/tpm/tpm-buf.c
index cad0048bcc3c6852de3633b7def9d9f604c83c29..e49a19fea3bdf645758891c7cef0548962e035e6 100644 (file)
--- a/drivers/char/tpm/tpm-buf.c
+++ b/drivers/char/tpm/tpm-buf.c
@@ -146,6 +146,26 @@ void tpm_buf_append_u32(struct tpm_buf *buf, const u32 value)
 }
 EXPORT_SYMBOL_GPL(tpm_buf_append_u32);
 
+/**
+ * tpm_buf_append_handle() - Add a handle
+ * @chip:      &tpm_chip instance
+ * @buf:       &tpm_buf instance
+ * @handle:    a TPM object handle
+ *
+ * Add a handle to the buffer, and increase the count tracking the number of
+ * handles in the command buffer. Works only for command buffers.
+ */
+void tpm_buf_append_handle(struct tpm_chip *chip, struct tpm_buf *buf, u32 handle)
+{
+       if (buf->flags & TPM_BUF_TPM2B) {
+               dev_err(&chip->dev, "Invalid buffer type (TPM2B)\n");
+               return;
+       }
+
+       tpm_buf_append_u32(buf, handle);
+       buf->handles++;
+}
+
 /**
  * tpm_buf_read() - Read from a TPM buffer
  * @buf:       &tpm_buf instance

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 1e856259219e2e9995b9fe7f799422d6c0bf3d87..dfdcbd009720607cc1fb8acd3ee6ba5edf695cae 100644 (file)
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -14,6 +14,10 @@
 #include "tpm.h"
 #include <crypto/hash_info.h>
 
+static bool disable_pcr_integrity;
+module_param(disable_pcr_integrity, bool, 0444);
+MODULE_PARM_DESC(disable_pcr_integrity, "Disable integrity protection of TPM2_PCR_Extend");
+
 static struct tpm2_hash tpm2_hash_map[] = {
        {HASH_ALGO_SHA1, TPM_ALG_SHA1},
        {HASH_ALGO_SHA256, TPM_ALG_SHA256},
@@ -232,18 +236,26 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
        int rc;
        int i;
 
-       rc = tpm2_start_auth_session(chip);
-       if (rc)
-               return rc;
+       if (!disable_pcr_integrity) {
+               rc = tpm2_start_auth_session(chip);
+               if (rc)
+                       return rc;
+       }
 
        rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_EXTEND);
        if (rc) {
-               tpm2_end_auth_session(chip);
+               if (!disable_pcr_integrity)
+                       tpm2_end_auth_session(chip);
                return rc;
        }
 
-       tpm_buf_append_name(chip, &buf, pcr_idx, NULL);
-       tpm_buf_append_hmac_session(chip, &buf, 0, NULL, 0);
+       if (!disable_pcr_integrity) {
+               tpm_buf_append_name(chip, &buf, pcr_idx, NULL);
+               tpm_buf_append_hmac_session(chip, &buf, 0, NULL, 0);
+       } else {
+               tpm_buf_append_handle(chip, &buf, pcr_idx);
+               tpm_buf_append_auth(chip, &buf, 0, NULL, 0);
+       }
 
        tpm_buf_append_u32(&buf, chip->nr_allocated_banks);
 
@@ -253,9 +265,11 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
                               chip->allocated_banks[i].digest_size);
        }
 
-       tpm_buf_fill_hmac_session(chip, &buf);
+       if (!disable_pcr_integrity)
+               tpm_buf_fill_hmac_session(chip, &buf);
        rc = tpm_transmit_cmd(chip, &buf, 0, "attempting extend a PCR value");
-       rc = tpm_buf_check_hmac_response(chip, &buf, rc);
+       if (!disable_pcr_integrity)
+               rc = tpm_buf_check_hmac_response(chip, &buf, rc);
 
        tpm_buf_destroy(&buf);
 

diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index 0739830904b2b3fc7aa88fbaa306b0aaf3e91d64..52d3523042fb8238bbd20a0ad195bfa916c49897 100644 (file)
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -237,9 +237,7 @@ void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
 #endif
 
        if (!tpm2_chip_auth(chip)) {
-               tpm_buf_append_u32(buf, handle);
-               /* count the number of handles in the upper bits of flags */
-               buf->handles++;
+               tpm_buf_append_handle(chip, buf, handle);
                return;
        }
 
@@ -272,6 +270,31 @@ void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
 }
 EXPORT_SYMBOL_GPL(tpm_buf_append_name);
 
+void tpm_buf_append_auth(struct tpm_chip *chip, struct tpm_buf *buf,
+                        u8 attributes, u8 *passphrase, int passphrase_len)
+{
+       /* 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);
+}
+
 /**
  * tpm_buf_append_hmac_session() - Append a TPM session element
  * @chip: the TPM chip structure
@@ -309,26 +332,8 @@ void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
 #endif
 
        if (!tpm2_chip_auth(chip)) {
-               /* 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);
+               tpm_buf_append_auth(chip, buf, attributes, passphrase,
+                                   passphrase_len);
                return;
        }
 

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 587b96b4418ed95c855342ceb8bd4cae7a83a5b7..20a40ade8030866ae973e088514941ca38f1d800 100644 (file)
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -421,6 +421,7 @@ void tpm_buf_append_u32(struct tpm_buf *buf, const u32 value);
 u8 tpm_buf_read_u8(struct tpm_buf *buf, off_t *offset);
 u16 tpm_buf_read_u16(struct tpm_buf *buf, off_t *offset);
 u32 tpm_buf_read_u32(struct tpm_buf *buf, off_t *offset);
+void tpm_buf_append_handle(struct tpm_chip *chip, struct tpm_buf *buf, u32 handle);
 
 /*
  * Check if TPM device is in the firmware upgrade mode.
@@ -505,6 +506,8 @@ void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
 void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
                                 u8 attributes, u8 *passphrase,
                                 int passphraselen);
+void tpm_buf_append_auth(struct tpm_chip *chip, struct tpm_buf *buf,
+                        u8 attributes, u8 *passphrase, int passphraselen);
 static inline void tpm_buf_append_hmac_session_opt(struct tpm_chip *chip,
                                                   struct tpm_buf *buf,
                                                   u8 attributes,