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Message-Id: <D5FJ9VCD1JBL.22MQYQHUYJLJ8@kernel.org>
Date: Thu, 07 Nov 2024 02:51:56 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>,
<linux-integrity@...r.kernel.org>, "Jonathan Corbet" <corbet@....net>,
"Peter Huewe" <peterhuewe@....de>, "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: Re: [PATCH] tpm: Opt-in in disable PCR encryption on TPM2 chips
On Thu Nov 7, 2024 at 2:47 AM EET, Jarkko Sakkinen wrote:
> 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.
> ---
Noticed a couple of things I missed after sending this (see below).
> .../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");
Should be in a single line in order to minimize the diff.
> + 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);
This is declared in wrong place as it has no outside callers. So I will
move it to drivers/char/tpm/tpm.h instead. Please correct if I'm
overlooking something.
> static inline void tpm_buf_append_hmac_session_opt(struct tpm_chip *chip,
> struct tpm_buf *buf,
> u8 attributes,
BR, Jarkko
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