Based recent discussions on LKML, provide preliminary bits of tpm_tis_core dependent drivers. Includes only bare essentials but can be extended later on case by case. This way some people may even want to read it later on. Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> --- v4: - Extended the text to address some of Stefan's concerns with v2. - Had to unfortunately remove Randy's reviewed-by because of this, given the amount of text added. v3: - Fixed incorrect buffer size: https://lore.kernel.org/linux-integrity/d957dbd3-4975-48d7-abc5-1a01c0959ea3@xxxxxxxxxxxxx/ v2: - Fixed errors reported by Randy: https://lore.kernel.org/all/aed28265-d677-491a-a045-24b351854b24@xxxxxxxxxxxxx/ - Improved the text a bit to have a better presentation. --- Documentation/security/tpm/index.rst | 1 + Documentation/security/tpm/tpm_tis.rst | 46 ++++++++++++++++++++++++++ 2 files changed, 47 insertions(+) create mode 100644 Documentation/security/tpm/tpm_tis.rst diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst index fc40e9f23c85..f27a17f60a96 100644 --- a/Documentation/security/tpm/index.rst +++ b/Documentation/security/tpm/index.rst @@ -5,6 +5,7 @@ Trusted Platform Module documentation .. toctree:: tpm_event_log + tpm_tis tpm_vtpm_proxy xen-tpmfront tpm_ftpm_tee diff --git a/Documentation/security/tpm/tpm_tis.rst b/Documentation/security/tpm/tpm_tis.rst new file mode 100644 index 000000000000..b448ea3db71d --- /dev/null +++ b/Documentation/security/tpm/tpm_tis.rst @@ -0,0 +1,46 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================= +TPM FIFO interface driver +========================= + +TCG PTP Specification defines two interface types: FIFO and CRB. The former is +based on sequenced read and write operations, and the latter is based on a +buffer containing the full command or response. + +FIFO (First-In-First-Out) interface is used by the tpm_tis_core dependent +drivers. Originally Linux had only a driver called tpm_tis, which covered +memory mapped (aka MMIO) interface but it was later on extended to cover other +physical interfaces supported by the TCG standard. + +For legacy compliance the original MMIO driver is called tpm_tis and the +framework for FIFO drivers is named as tpm_tis_core. The postfix "tis" in +tpm_tis comes from the TPM Interface Specification, which is the hardware +interface specification for TPM 1.x chips. + +Communication is based on a 20 KiB buffer shared by the TPM chip through a +hardware bus or memory map, depending on the physical wiring. The buffer is +further split into five equal-size 4 KiB buffers, which provide equivalent +sets of registers for communication between the CPU and TPM. These +communication endpoints are called localities in the TCG terminology. + +When the kernel wants to send commands to the TPM chip, it first reserves +locality 0 by setting the requestUse bit in the TPM_ACCESS register. The bit is +cleared by the chip when the access is granted. Once it completes its +communication, the kernel writes the TPM_ACCESS.activeLocality bit. This +informs the chip that the locality has been relinquished. + +Pending localities are served in order by the chip in descending order, one at +a time: + +- Locality 0 has the lowest priority. +- Locality 5 has the highest priority. + +Further information on the purpose and meaning of the localities can be found +in section 3.2 of the TCG PC Client Platform TPM Profile Specification. + +References +========== + +TCG PC Client Platform TPM Profile (PTP) Specification +https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ -- 2.44.0
