Re: [PATCH v3] tpm: Opt-in in disable PCR integrity protection

[Mimi Zohar <zohar@xxxxxxxxxxxxx>]

On Wed, 2024-11-13 at 02:24 +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 extend operations (i.e. TPM2_PCR_Extend).
> 
> Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> Link: https://lore.kernel.org/linux-integrity/20241015193916.59964-1-zohar@xxxxxxxxxxxxx/
> Fixes: 6519fea6fd37 ("tpm: add hmac checks to tpm2_pcr_extend()")
> Co-developed-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> Co-developed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

The module_param variable documentation needs to be updated to reflect the
actual module_param variable 'disable_pcr_integrity'.

Otherwise,
Tested-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>

> ---
> v3:
> - Please test this too ;-) I did quick testing only.
> - Fixed the reported glitches and mistakes.
> v2:
> - Followed Mimi's suggestions.
> ---
>  .../admin-guide/kernel-parameters.txt         |  9 ++++
>  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, 82 insertions(+), 31 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1666576acc0e..7107ad322b2e 100644
> --- 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_protection= [HW,TPM]

-> tpm.disable_pcr_integrity=

> +			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 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..dfdcbd009720 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;
> +module_param(disable_pcr_integrity, bool, 0444);
> +MODULE_PARM_DESC(disable_pcr_integrity, "Disable integrity protection of TPM2_PCR_Extend");

'disable_pcr_integrity' doesn't match the documentation.

> +
>  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,


thanks,

Mimi