From: Paul Menzel <pmenzel@molgen.mpg.de>
To: Douglas Anderson <dianders@chromium.org>,
Peter Huewe <peterhuewe@gmx.de>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: Andrey Pronin <apronin@chromium.org>,
Stephen Boyd <swboyd@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tpm_tis_spi: Don't send anything during flow control
Date: Fri, 29 May 2020 10:33:28 +0200 [thread overview]
Message-ID: <c628b545-f883-3c2e-cabf-944f6a313bf2@molgen.mpg.de> (raw)
In-Reply-To: <20200528151912.1.Id689a39ce8d1ec6f29f4287277ad977ff4f57d7d@changeid>
Dear Douglas,
Thank you for the patch.
Am 29.05.20 um 00:19 schrieb Douglas Anderson:
> During flow control we are just reading from the TPM, yet our spi_xfer
> has the tx_buf and rx_buf both non-NULL which means we're requesting a
> full duplex transfer.
>
> SPI is always somewhat of a full duplex protocol anyway and in theory
> the other side shouldn't really be looking at what we're sending it
> during flow control, but it's still a bit ugly to be sending some
> "random" data when we shouldn't.
>
> The default tpm_tis_spi_flow_control() tries to address this by
> setting 'phy->iobuf[0] = 0'. This partially avoids the problem of
> sending "random" data, but since our tx_buf and rx_buf both point to
> the same place I believe there is the potential of us sending the
> TPM's previous byte back to it if we hit the retry loop.
>
> Another flow control implementation, cr50_spi_flow_control(), doesn't
> address this at all.
>
> Let's clean this up and just make the tx_buf NULL before we call
> flow_control(). Not only does this ensure that we're not sending any
> "random" bytes but it also possibly could make the SPI controller
> behave in a slightly more optimal way.
>
> NOTE: no actual observed problems are fixed by this patch--it's was
> just made based on code inspection.
s/it's was/it was/
Were you able to test this? Maybe in the “Chromebook QA arsenal”? Are
you already running it in production on Google Chrome OS devices?
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
>
> drivers/char/tpm/tpm_tis_spi_main.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_tis_spi_main.c b/drivers/char/tpm/tpm_tis_spi_main.c
> index d96755935529..8d2c581a93c6 100644
> --- a/drivers/char/tpm/tpm_tis_spi_main.c
> +++ b/drivers/char/tpm/tpm_tis_spi_main.c
> @@ -53,8 +53,6 @@ static int tpm_tis_spi_flow_control(struct tpm_tis_spi_phy *phy,
>
> if ((phy->iobuf[3] & 0x01) == 0) {
> // handle SPI wait states
> - phy->iobuf[0] = 0;
> -
> for (i = 0; i < TPM_RETRY; i++) {
> spi_xfer->len = 1;
> spi_message_init(&m);
> @@ -104,6 +102,8 @@ int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
> if (ret < 0)
> goto exit;
>
> + /* Flow control transfers are receive only */
> + spi_xfer.tx_buf = NULL;
> ret = phy->flow_control(phy, &spi_xfer);
> if (ret < 0)
> goto exit;
> @@ -113,9 +113,8 @@ int tpm_tis_spi_transfer(struct tpm_tis_data *data, u32 addr, u16 len,
> spi_xfer.delay.value = 5;
> spi_xfer.delay.unit = SPI_DELAY_UNIT_USECS;
>
> - if (in) {
> - spi_xfer.tx_buf = NULL;
> - } else if (out) {
> + if (out) {
> + spi_xfer.tx_buf = phy->iobuf;
> spi_xfer.rx_buf = NULL;
> memcpy(phy->iobuf, out, transfer_len);
> out += transfer_len;
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Kind regards,
Paul
next prev parent reply other threads:[~2020-05-29 8:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 22:19 [PATCH] tpm_tis_spi: Don't send anything during flow control Douglas Anderson
2020-05-29 8:33 ` Paul Menzel [this message]
2020-05-29 15:37 ` Doug Anderson
2020-06-01 1:47 ` Jarkko Sakkinen
2020-06-01 22:54 ` Doug Anderson
2020-06-04 9:40 ` Jarkko Sakkinen
2020-06-04 13:48 ` Doug Anderson
2020-06-16 20:44 ` Jarkko Sakkinen
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