The TPM device provides the random number generator(RNG) functionality, whereby sending a command to the TPM device results in the TPM device responding with random bytes.
There was a discussion on the mailing list earlier[1], where it was explained that platforms with a TPM device can install the EFI_RNG_PROTOCOL for getting the random bytes instead of populating the dtb with the kaslr-seed property. That would make it possible to measure the dtb.
This patchset moves the already existing functions for getting random bytes from the TPM device to drivers complying with the RNG uclass. This is done since the EFI_RNG_PROTOCOL's get_rng routine uses the RNG uclass's dm_rng_read api to get the random bytes.
The TPM uclass driver adds the RNG child device as part of it's post_probe function. The TPM uclass driver's child_pre_probe function initialises the TPM parent device for use -- this enables the RNG child device to be used subsequently.
Some additional changes have also been made to facilitate the use of the RNG devices, including extending the 'rng' command to take the RNG device as one of the command-line parameters.
This series depends on a patch[2] from Simon Glass for moving the TPM device version detection functions to the tpm_api.h header as static inline functions. [1] - https://lore.kernel.org/u-boot/20220103120738.47835-1-ilias.apalodimas@linar... [2] - https://lore.kernel.org/u-boot/20220301001125.1554442-2-sjg@chromium.org/T/#...
Changes since V4:
* Call the existing tpm_get_random API function from the TPM RNG driver, instead of the tpm{1,2}_get_random API's * Introduce a new Kconfig symbol TPM_RNG and build the corresponding driver if the symbol is enabled * Change the last parameter of the tpm_get_random API to have a data type of size_t instead of u32 to comply with the RNG driver model API * Put a check for CONFIG_TPM_RNG for binding the RNG device with it's driver in the post_probe callback instead of putting CONFIG_{SPL,TPL}_BUILD guards * Use uclass_get_device_by_seq API to get the RNG device as suggested by Simon * Add a new patch based on review comments from Simon to not use the malloc call * Reflect the fact that a maximum of 64 bytes can be read on each invocation of the 'rng' command in the rng document
Sughosh Ganu (9): tpm: rng: Change tpm_get_random to return an int tpm: Fix the return type of tpm_startup tpm: rng: Add driver model interface for TPM RNG device tpm: Add the RNG child device qemu: arm: Remove platform specific function to get RNG device cmd: rng: Add support for selecting RNG device cmd: rng: Use a statically allocated array for random bytes doc: rng: Add documentation for the rng command test: rng: Add a UT testcase for the rng command
board/emulation/qemu-arm/qemu-arm.c | 42 ----------------------------- cmd/Kconfig | 1 + cmd/rng.c | 42 ++++++++++++++++++----------- doc/usage/index.rst | 1 + doc/usage/rng.rst | 26 ++++++++++++++++++ drivers/rng/Kconfig | 7 +++++ drivers/rng/Makefile | 1 + drivers/rng/tpm_rng.c | 23 ++++++++++++++++ drivers/tpm/tpm-uclass.c | 29 +++++++++++++++++--- include/tpm-v1.h | 4 +-- include/tpm-v2.h | 4 +-- include/tpm_api.h | 6 ++--- lib/Kconfig | 1 + lib/tpm-v1.c | 16 ++++++----- lib/tpm-v2.c | 9 ++++--- lib/tpm_api.c | 19 ++++++++----- test/dm/rng.c | 29 ++++++++++++++++++++ 17 files changed, 175 insertions(+), 85 deletions(-) create mode 100644 doc/usage/rng.rst create mode 100644 drivers/rng/tpm_rng.c