[PATCH v2 07/10] tpm: rng: Move the TPM RNG functionality to driver model

[Sughosh Ganu]

hi Simon,

On Thu, 3 Mar 2022 at 09:17, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Sughosh,
>
> On Tue, 1 Mar 2022 at 21:36, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
> >
> > hi Simon,
> >
> > On Tue, 1 Mar 2022 at 20:28, Simon Glass <sjg at chromium.org> wrote:
> > >
> > > Hi Sughosh,
> > >
> > > On Mon, 28 Feb 2022 at 05:07, Sughosh Ganu <sughosh.ganu at linaro.org> wrote:
> > > >
> > > > Currently, the TPM random number generator(RNG) functions are defined
> > > > as part of the library functions under the corresponding tpm files for
> > > > tpmv1 and tpmv2. Move the RNG functionality under TPM RNG drivers
> > > > complying with the driver model.
> > > >
> > > > Also make changes to the tpm_get_random function to have it call the
> > > > TPM RNG driver functions instead of the library functions.
> > > >
> > > > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> > > > ---
> > > >
> > > > Changes since V1:
> > > > * Added existing copyrights for the rng functions taken from the tpm
> > > >   library routines
> > > > * Return -EIO for TPM command returning an error
> > > > * Simplify the logic in tpm_get_random based on the review comments
> > > >   from Ilias
> > > >
> > > >  drivers/rng/Makefile   |  1 +
> > > >  drivers/rng/tpm1_rng.c | 87 ++++++++++++++++++++++++++++++++++++++++++
> > > >  drivers/rng/tpm2_rng.c | 86 +++++++++++++++++++++++++++++++++++++++++
> > > >  lib/tpm-v1.c           | 44 ---------------------
> > > >  lib/tpm-v2.c           | 44 ---------------------
> > > >  lib/tpm_api.c          | 23 +++++++++--
> > > >  6 files changed, 193 insertions(+), 92 deletions(-)
> > > >  create mode 100644 drivers/rng/tpm1_rng.c
> > > >  create mode 100644 drivers/rng/tpm2_rng.c
> > > >
> > > > diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
> > > > index 39f7ee3f03..129cfbd006 100644
> > > > --- a/drivers/rng/Makefile
> > > > +++ b/drivers/rng/Makefile
> > > > @@ -10,3 +10,4 @@ obj-$(CONFIG_RNG_MSM) += msm_rng.o
> > > >  obj-$(CONFIG_RNG_STM32MP1) += stm32mp1_rng.o
> > > >  obj-$(CONFIG_RNG_ROCKCHIP) += rockchip_rng.o
> > > >  obj-$(CONFIG_RNG_IPROC200) += iproc_rng200.o
> > > > +obj-$(CONFIG_TPM) += tpm1_rng.o tpm2_rng.o
> > > > diff --git a/drivers/rng/tpm1_rng.c b/drivers/rng/tpm1_rng.c
> > > > new file mode 100644
> > > > index 0000000000..7e629756b3
> > > > --- /dev/null
> > > > +++ b/drivers/rng/tpm1_rng.c
> > > > @@ -0,0 +1,87 @@
> > > > +// SPDX-License-Identifier: GPL-2.0+
> > > > +/*
> > > > + * Copyright (c) 2013 The Chromium OS Authors.
> > > > + * Coypright (c) 2013 Guntermann & Drunck GmbH
> > > > + * Copyright (c) 2022, Linaro Limited
> > > > + */
> > > > +
> > > > +#include <common.h>
> > > > +#include <dm.h>
> > > > +#include <rng.h>
> > > > +#include <tpm-utils.h>
> > > > +#include <tpm-v1.h>
> > > > +
> > > > +#include <linux/errno.h>
> > > > +
> > > > +#define TPM_HEADER_SIZE                10
> > > > +
> > > > +#define TPMV1_DATA_OFFSET      14
> > > > +
> > > > +/**
> > > > + * tpm1_rng_read() - Read the random bytes from TPMv1 device
> > > > + * @param dev          TPMv1 RNG device
> > > > + * @param data         data buffer to write random bytes
> > > > + * @param count                number of random bytes to read from
> > > > + *                      the device
> > > > + *
> > > > + * Function to read the random bytes from the RNG pseudo device
> > > > + * built into the TPMv1 device. Reads 'count' number of bytes
> > > > + * from the random number generator and copies them into the
> > > > + * 'data' buffer.
> > > > + *
> > > > + * Return: 0 if OK, -ve on error.
> > > > + *
> > > > + */
> > > > +static int tpm1_rng_read(struct udevice *dev, void *data, size_t count)
> > > > +{
> > > > +       const u8 command[14] = {
> > > > +               0x0, 0xc1,              /* TPM_TAG */
> > > > +               0x0, 0x0, 0x0, 0xe,     /* parameter size */
> > > > +               0x0, 0x0, 0x0, 0x46,    /* TPM_COMMAND_CODE */
> > > > +       };
> > > > +       const size_t length_offset = TPM_HEADER_SIZE;
> > > > +       const size_t data_size_offset = TPM_HEADER_SIZE;
> > > > +       const size_t data_offset = TPMV1_DATA_OFFSET;
> > > > +       u8 buf[COMMAND_BUFFER_SIZE], response[COMMAND_BUFFER_SIZE];
> > > > +       size_t response_length = sizeof(response);
> > > > +       u32 data_size;
> > > > +       u8 *out = data;
> > > > +
> > >
> > > The current model is that all TPM calls are set up in lib/tpm and I
> > > don't think we should change it. You should be able to move these
> > > functions into lib/tpm and add your random_read function to tpm_api.h
> >
> > I moved these functions under separate drivers as I thought that
> > looked cleaner as against exporting the driver interface in
>
> But you are now creating TPM messages in a different file so I don't
> think it is cleaner. The message pack/unpack should happen in the
> tpm_... functions.
>
> > tpm-v{1,2}.c. If you strongly feel that these should remain under
> > lib/tpm, I will make the change. But I believe you do not have a
> > problem with exporting these rng functions as part of the driver
> > model. We do need that so that the EFI_RNG_PROTOCOL can use these for
> > getting the random bytes.
>
> I think you might misunderstand me. I mean that the code that calls
> pack_byte_string() should be in lib/ like the other code. I agree that
> the driver should be were you have put it, I just don't like having
> the tpm message creation in that driver. It should call a tpm_...
> function to create and send the message, like elsewhere.

I tried putting a wrapper around the pack/unpack functions like you
suggest, but it is getting more complicated than required. Even after
putting the wrapper, there still is an issue of tpm_sendrecv being
declared in tpm-utils.h, along with some other necessary macros like
COMMAND_BUFFER_SIZE. You have mentioned in another review that you
don't want tpm-utils.h to be moved to the include/ directory. If we
are not to move tpm-utils.h and also not call functions like
pack_byte_string directly from the driver, I feel it will be easier to
simply export the rng functions to the driver model from within
lib/tpm/ instead of moving them under drivers/rng/. Will you be okay
with this.

-sughosh

>
> Regards,
> Simon