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Message-ID: <20241107004708.108667-1-jarkko@kernel.org>
Date: Thu, 7 Nov 2024 02:47:07 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: linux-integrity@...r.kernel.org,
Jonathan Corbet <corbet@....net>,
Peter Huewe <peterhuewe@....de>,
Jarkko Sakkinen <jarkko@...nel.org>,
Jason Gunthorpe <jgg@...pe.ca>,
James Bottomley <James.Bottomley@...senPartnership.com>
Cc: Mimi Zohar <zohar@...ux.ibm.com>,
Roberto Sassu <roberto.sassu@...wei.com>,
linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] tpm: Opt-in in disable PCR encryption on TPM2 chips
From: Mimi Zohar <zohar@...ux.ibm.com>
The initial encrypted HMAC session feature added TPM bus encryption to
various in-kernel TPM operations. This can cause performance bottlenecks
with IMA, as it heavily utilizes PCR extend operations.
In order to address this performance issue, introduce disable_encrypt_pcrs
kernel command-line parameter to the TPM driver.
Cc: James Bottomley <James.Bottomley@...senPartnership.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()")
Co-developed-by: Roberto Sassu <roberto.sassu@...wei.com>
Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
Co-developed-by: Jarkko Sakkinen <jarkko@...nel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
---
v1:
- Derived from the earlier RFC patch with a different parameter scope,
cleaner commit message and some other tweaks. I decided to create
something because I did not noticed any progress. Note only compile
tested as I wanted to get something quickly out.
---
.../admin-guide/kernel-parameters.txt | 10 ++++
drivers/char/tpm/tpm2-cmd.c | 33 ++++++++---
drivers/char/tpm/tpm2-sessions.c | 59 +++++++++++--------
include/linux/tpm.h | 4 ++
4 files changed, 74 insertions(+), 32 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1518343bbe22..e27517e1a26f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6727,6 +6727,16 @@
torture.verbose_sleep_duration= [KNL]
Duration of each verbose-printk() sleep in jiffies.
+ tpm.disable_encrypt_pcrs= [HW,TPM]
+ Do not protect PCR registers from unintended physical
+ access, or interposers in the bus by the means of
+ having an encrypted and 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/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 1e856259219e..6ec307b1cb99 100644
--- 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_encrypt_pcrs;
+module_param(disable_encrypt_pcrs, bool, 0444);
+MODULE_PARM_DESC(disable_encrypt_pcrs, "Disable TPM2_PCR_Extend encryption");
+
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_encrypt_pcrs) {
+ 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_encrypt_pcrs)
+ 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_encrypt_pcrs) {
+ 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, NULL);
+ tpm_buf_append_auth(chip, &buf, 0, NULL, 0);
+ }
tpm_buf_append_u32(&buf, chip->nr_allocated_banks);
@@ -253,9 +265,12 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
chip->allocated_banks[i].digest_size);
}
- 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_encrypt_pcrs)
+ tpm_buf_fill_hmac_session(chip, &buf);
+ rc = tpm_transmit_cmd(chip, &buf, 0,
+ "attempting extend a PCR value");
+ if (!disable_encrypt_pcrs)
+ 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 42df980168b6..02897debc3fa 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -205,6 +205,14 @@ static int tpm2_read_public(struct tpm_chip *chip, u32 handle, char *name)
}
#endif /* CONFIG_TCG_TPM2_HMAC */
+void tpm_buf_append_handle(struct tpm_chip *chip, struct tpm_buf *buf,
+ u32 handle, u8 *name)
+{
+ tpm_buf_append_u32(buf, handle);
+ /* count the number of handles in the upper bits of flags */
+ buf->handles++;
+}
+
/**
* tpm_buf_append_name() - add a handle area to the buffer
* @chip: the TPM chip structure
@@ -237,9 +245,7 @@ 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, name);
return;
}
@@ -272,6 +278,31 @@ 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 +340,8 @@ 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 587b96b4418e..4892cd004530 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -502,9 +502,13 @@ static inline struct tpm2_auth *tpm2_chip_auth(struct tpm_chip *chip)
void tpm_buf_append_name(struct tpm_chip *chip, struct tpm_buf *buf,
u32 handle, u8 *name);
+void tpm_buf_append_handle(struct tpm_chip *chip, struct tpm_buf *buf,
+ u32 handle, u8 *name);
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,
--
2.47.0
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