linux-kernel - Re: [PATCH] tpm: Define TPM2_SPACE_BUFFER_SIZE to replace the use of PAGE

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Date:   Fri, 26 Jun 2020 12:47:02 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org
Cc:     stable@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: Define TPM2_SPACE_BUFFER_SIZE to replace the use of
 PAGE_SIZE

On 6/26/20 10:34 AM, Jarkko Sakkinen wrote:
> The size of the buffers for storing context's and sessions can vary from
> arch to arch as PAGE_SIZE can be anything between 4 kB and 256 kB (the
> maximum for PPC64). Define a fixed buffer size set to 16 kB. This should
> be enough for most use with three handles (that is how many we allow at
> the moment).
>
> Reported-by: Stefan Berger <stefanb@...ux.ibm.com>
> Cc: stable@...r.kernel.org
> Fixes: 745b361e989a ("tpm: infrastructure for TPM spaces")
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> ---
>   drivers/char/tpm/tpm2-space.c | 27 ++++++++++++++++-----------
>   1 file changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> index 982d341d8837..9bef646093d1 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -15,6 +15,8 @@
>   #include <asm/unaligned.h>
>   #include "tpm.h"
>   
> +#define TPM2_SPACE_BUFFER_SIZE		16384 /* 16 kB */
> +
>   enum tpm2_handle_types {
>   	TPM2_HT_HMAC_SESSION	= 0x02000000,
>   	TPM2_HT_POLICY_SESSION	= 0x03000000,
> @@ -40,11 +42,11 @@ static void tpm2_flush_sessions(struct tpm_chip *chip, struct tpm_space *space)
>   
>   int tpm2_init_space(struct tpm_space *space)
>   {
> -	space->context_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	space->context_buf = kzalloc(TPM2_SPACE_BUFFER_SIZE, GFP_KERNEL);
>   	if (!space->context_buf)
>   		return -ENOMEM;
>   
> -	space->session_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	space->session_buf = kzalloc(TPM2_SPACE_BUFFER_SIZE, GFP_KERNEL);
>   	if (space->session_buf == NULL) {
>   		kfree(space->context_buf);
>   		return -ENOMEM;
> @@ -311,8 +313,10 @@ int tpm2_prepare_space(struct tpm_chip *chip, struct tpm_space *space, u8 *cmd,
>   	       sizeof(space->context_tbl));
>   	memcpy(&chip->work_space.session_tbl, &space->session_tbl,
>   	       sizeof(space->session_tbl));
> -	memcpy(chip->work_space.context_buf, space->context_buf, PAGE_SIZE);
> -	memcpy(chip->work_space.session_buf, space->session_buf, PAGE_SIZE);
> +	memcpy(chip->work_space.context_buf, space->context_buf,
> +	       TPM2_SPACE_BUFFER_SIZE);
> +	memcpy(chip->work_space.session_buf, space->session_buf,
> +	       TPM2_SPACE_BUFFER_SIZE);
>   
>   	rc = tpm2_load_space(chip);
>   	if (rc) {
> @@ -492,8 +496,8 @@ static int tpm2_save_space(struct tpm_chip *chip)
>   			continue;
>   
>   		rc = tpm2_save_context(chip, space->context_tbl[i],
> -				       space->context_buf, PAGE_SIZE,
> -				       &offset);
> +				       space->context_buf,
> +				       TPM2_SPACE_BUFFER_SIZE, &offset);
>   		if (rc == -ENOENT) {
>   			space->context_tbl[i] = 0;
>   			continue;
> @@ -509,9 +513,8 @@ static int tpm2_save_space(struct tpm_chip *chip)
>   			continue;
>   
>   		rc = tpm2_save_context(chip, space->session_tbl[i],
> -				       space->session_buf, PAGE_SIZE,
> -				       &offset);
> -
> +				       space->session_buf,
> +				       TPM2_SPACE_BUFFER_SIZE, &offset);
>   		if (rc == -ENOENT) {
>   			/* handle error saving session, just forget it */
>   			space->session_tbl[i] = 0;
> @@ -557,8 +560,10 @@ int tpm2_commit_space(struct tpm_chip *chip, struct tpm_space *space,
>   	       sizeof(space->context_tbl));
>   	memcpy(&space->session_tbl, &chip->work_space.session_tbl,
>   	       sizeof(space->session_tbl));
> -	memcpy(space->context_buf, chip->work_space.context_buf, PAGE_SIZE);
> -	memcpy(space->session_buf, chip->work_space.session_buf, PAGE_SIZE);
> +	memcpy(space->context_buf, chip->work_space.context_buf,
> +	       TPM2_SPACE_BUFFER_SIZE);
> +	memcpy(space->session_buf, chip->work_space.session_buf,
> +	       TPM2_SPACE_BUFFER_SIZE);


work_space.session_buf and context_buf also need allocation changes, 
otherwise we read from a smaller buffer here. See comment to other patch 
about tpm-chip.c .


>   
>   	return 0;
>   out: