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Message-ID: <e015a939893d35efe75e598152725adcc2befdd8.camel@linux.ibm.com>
Date: Thu, 07 Nov 2024 08:44:31 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
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: Roberto Sassu <roberto.sassu@...wei.com>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tpm: Opt-in in disable PCR integrity protection
On Thu, 2024-11-07 at 11:51 +0200, Jarkko Sakkinen wrote:
> 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 extension.
>
> 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>
> Co-developed-by: Mimi Zohar <zohar@...ux.ibm.com>
> Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> ---
> v2:
> - Move tpm_buf_append_handle() to the correct file, remove spurious
> parameter (name), include error on TPM2B and add documentation.
> Keep the declaration in linux/tpm.h despite not exported as it
> is easiest to maintain tpm_buf_* in a single header.
> - Rename kernel command-line option as "disable_pcr_integrity_protection",
> as Mimi pointed out it does not carry SA_ENCRYPT flag.
> 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/tpm-buf.c | 20 ++++++++
> drivers/char/tpm/tpm2-cmd.c | 30 ++++++++---
> drivers/char/tpm/tpm2-sessions.c | 51 ++++++++++---------
> include/linux/tpm.h | 3 ++
> 5 files changed, 83 insertions(+), 31 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1518343bbe22..9fc406b20a74 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_pcr_integrity_protection= [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
"encrypted" isn't needed here.
> + 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 cad0048bcc3c..e49a19fea3bd 100644
> --- 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 1e856259219e..cc443bcf15e8 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_pcr_integrity_protection;
> +module_param(disable_pcr_integrity_protection, bool, 0444);
> +MODULE_PARM_DESC(disable_pcr_integrity_protection, "Disable TPM2_PCR_Extend encryption");
I like the name 'disable_pcr_integrity_protection. However, the name and
description doesn't match. Replace 'encryption' with 'integrity protection'.
> +
> 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_protection) {
> + 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_protection)
> + 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_protection) {
> + tpm_buf_append_name(chip, &buf, pcr_idx);
tpm_buf_append_name() parameters didn't change. Don't remove the 'name' field
here.
> + tpm_buf_append_hmac_session(chip, &buf, 0, NULL, 0);
> + } else {
> + tpm_buf_append_handle(chip, &buf, pcr_idx);
Or here.
> + tpm_buf_append_auth(chip, &buf, 0, NULL, 0);
> + }
>
> tpm_buf_append_u32(&buf, chip->nr_allocated_banks);
>
>
Mimi
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