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tpm: Opt-in in disable PCR integrity protection

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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: 6519fea6fd ("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>
This commit is contained in:
Jarkko Sakkinen 2024-11-13 07:54:12 +02:00
parent 14b6320953
commit 27184f8905
5 changed files with 82 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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

20
drivers/char/tpm/tpm-buf.c
View File

@ -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

30
drivers/char/tpm/tpm2-cmd.c
View File

@ -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);

51
drivers/char/tpm/tpm2-sessions.c
View File

@ -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;
}

3
include/linux/tpm.h
View File

@ -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,