linux-kernel - Re: [PATCH v2] tpm: tpm2-space: Resize session and context buffers dynamically

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Message-ID: <a6444592-234b-d77e-7403-812e19691e72@linux.ibm.com>
Date:   Thu, 25 Jun 2020 17:38:03 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org
Cc:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Alexey Klimov <aklimov@...hat.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tpm: tpm2-space: Resize session and context buffers
 dynamically

On 6/25/20 12:38 AM, Jarkko Sakkinen wrote:
> Re-allocate context and session buffers when needed. Scale them in page
> increments so that the reallocation is only seldomly required, and thus
> causes minimal stress to the system. Add a static maximum limit of four
> pages for buffer sizes.
>
> Cc: James Bottomley <James.Bottomley@...senPartnership.com>
> Suggested-by: Stefan Berger <stefanb@...ux.ibm.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> ---
> Tested only for compilation.
> v2: TPM2_SPACE_DEFAULT_BUFFER_SIZE
>   drivers/char/tpm/tpm2-space.c | 87 ++++++++++++++++++++++++-----------
>   include/linux/tpm.h           |  6 ++-
>   2 files changed, 64 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
> index 982d341d8837..b8ece01d6afb 100644
> --- a/drivers/char/tpm/tpm2-space.c
> +++ b/drivers/char/tpm/tpm2-space.c
> @@ -15,6 +15,9 @@
>   #include <asm/unaligned.h>
>   #include "tpm.h"
>   
> +#define TPM2_SPACE_DEFAULT_BUFFER_SIZE	PAGE_SIZE
> +#define TPM2_SPACE_MAX_BUFFER_SIZE	(4 * PAGE_SIZE)
> +
>   enum tpm2_handle_types {
>   	TPM2_HT_HMAC_SESSION	= 0x02000000,
>   	TPM2_HT_POLICY_SESSION	= 0x03000000,
> @@ -557,8 +588,10 @@ 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,
> +	       space->context_size);


You have to allocate the max size the in tpm_chip_alloc (tpm-chip.c):

    chip->work_space.context_buf = kzalloc(TPM2_SPACE_MAX_BUFFER_SIZE, 
GFP_KERNEL);


> +	memcpy(space->session_buf, chip->work_space.session_buf,
> +	       space->session_size);
>   


same for this


>   	return 0;
>   out:
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 03e9b184411b..9ea39e8f7162 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -92,10 +92,12 @@ enum tpm_duration {
>   #define TPM_PPI_VERSION_LEN		3
>   
>   struct tpm_space {
> +	u8  *context_buf;
> +	u8  *session_buf;
> +	u32 context_size;
> +	u32 session_size;
>   	u32 context_tbl[3];
> -	u8 *context_buf;
>   	u32 session_tbl[3];
> -	u8 *session_buf;
>   };
>   
>   struct tpm_bios_log {