Thanks Tim On Thu, 28 Mar 2024 at 00:12, Tim Harvey <thar...@gateworks.com> wrote: > > Instead of displaying what looks like an error message if a > gpio-reset dt prop is missing for a TPM display a warning that > having a gpio reset on a TPM should not be used for a secure production > device. > > TCG TIS spec [1] says: > "The TPM_Init (LRESET#/SPI_RST#) signal MUST be connected to the > platform CPU Reset signal such that it complies with the requirements > specified in section 1.2.7 HOST Platform Reset in the PC Client > Implementation Specification for Conventional BIOS." > > The reasoning is that you should not be able to toggle a GPIO and reset > the TPM without resetting the CPU as well because if an attacker can > break into your OS via an OS level security flaw they can then reset the > TPM via GPIO and replay the measurements required to unseal keys > that you have otherwise protected. > > [1] > https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClientTPMInterfaceSpecification_TIS__1-3_27_03212013.pdf > > Signed-off-by: Tim Harvey <thar...@gateworks.com> > --- > v2: change the message to a warning and update commit desc/log > --- > drivers/tpm/tpm2_tis_spi.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/tpm/tpm2_tis_spi.c b/drivers/tpm/tpm2_tis_spi.c > index de9cf8f21e07..c9c83f6f0fc8 100644 > --- a/drivers/tpm/tpm2_tis_spi.c > +++ b/drivers/tpm/tpm2_tis_spi.c > @@ -237,14 +237,14 @@ static int tpm_tis_spi_probe(struct udevice *dev) > /* legacy reset */ > ret = gpio_request_by_name(dev, "gpio-reset", 0, > &reset_gpio, GPIOD_IS_OUT); > - if (ret) { > - log(LOGC_NONE, LOGL_NOTICE, > - "%s: missing reset GPIO\n", __func__); > + if (ret) > goto init; > - } > log(LOGC_NONE, LOGL_NOTICE, > "%s: gpio-reset is deprecated\n", __func__); > } > + log(LOGC_NONE, LOGL_WARNING, > + "%s: TPM gpio reset should not be used on secure > production devices\n", > + dev->name); > dm_gpio_set_value(&reset_gpio, 1); > mdelay(1); > dm_gpio_set_value(&reset_gpio, 0); > -- > 2.25.1 >
Reviewed-by: Ilias Apalodimas <ilias.apalodi...@linaro.org>
