On 16/05/24 09:09:50, Miquel Raynal wrote: > Hi Tim, > > thar...@gateworks.com wrote on Wed, 15 May 2024 16:21:38 -0700: > > > 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. > > > > Additionally restructure the code for improved readability allowing for > > removal of the init label. > > > > Before: > > - board with no reset gpio > > u-boot=> tpm init && tpm info > > tpm_tis_spi_probe: missing reset GPIO > > tpm@1 v2.0: VendorID 0x1114, DeviceID 0x3205, RevisionID 0x01 [open] > > - board with a reset gpio > > u-boot=> tpm init && tpm info > > tpm@1 v2.0: VendorID 0x1114, DeviceID 0x3205, RevisionID 0x01 [open] > > > > After: > > - board with no reset gpio > > u-boot=> tpm init && tpm info > > tpm@1 v2.0: VendorID 0x1114, DeviceID 0x3205, RevisionID 0x01 [open] > > - board with a reset gpio > > u-boot=> tpm init && tpm info > > tpm@1: TPM gpio reset should not be used on secure production devices > > tpm@1 v2.0: VendorID 0x1114, DeviceID 0x3205, RevisionID 0x01 [open] > > > > [1] > > https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClientTPMInterfaceSpecification_TIS__1-3_27_03212013.pdf > > > > Signed-off-by: Tim Harvey <thar...@gateworks.com> > > Looks way cleaner, thanks. > > Reviewed-by: Miquel Raynal <miquel.ray...@bootlin.com> > > Miquèl
nice. if needed Signed-off-by: Jorge Ramirez-Ortiz <jo...@foundries.io>
