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

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Date:   Fri, 26 Jun 2020 14:50:30 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        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 Thu, Jun 25, 2020 at 05:38:03PM -0400, Stefan Berger wrote:
> 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

That is not true. They should allocated as 4 kB in the dynamic scaling
scheme. The idea is to use krealloc() to increase the buffer size.

/Jarkko