This series will automatically add /chosen/kaslr-seed to the dt if DM_RNG is enabled during the boot process.
If RANDOMIZE_BASE is enabled in the Linux kernel instructing it to randomize the virtual address at which the kernel image is loaded, it expects entropy to be provided by the bootloader by populating /chosen/kaslr-seed with a 64-bit value from source of entropy at boot.
If we have DM_RNG enabled populate this value automatically when fdt_chosen is called. We skip this if ARMV8_SEC_FIRMWARE_SUPPORT is enabled as its implementation uses a different source of entropy that is not yet implemented as DM_RNG. We also skip this if MEASURED_BOOT is enabled as in that case any modifications to the dt will cause measured boot to fail (although there are many other places the dt is altered).
As this fdt node is added elsewhere create a library function and use it to deduplicate code. We will provide a parameter to overwrite the node if present.
For our automatic injection, we will use the first rng device and not overwrite if already present with a non-zero value (which may have been populated by an earlier boot stage). This way if a board specific ft_board_setup() function wants to customize this behavior it can call fdt_kaslrseed with a rng device index of its choosing and set overwrite true.
Note that the kalsrseed command (CMD_KASLRSEED) is likely pointless now but left in place in case boot scripts exist that rely on this command existing and returning success. An informational message is printed to alert users of this command that it is likely no longer needed.
Note that the Kernel's EFI STUB only relies on EFI_RNG_PROTOCOL for randomization and completely ignores the kaslr-seed for its own randomness needs (i.e the randomization of the physical placement of the kernel). It gets weeded out from the DTB that gets handed over via efi_install_fdt() as it would also mess up the measured boot DTB TPM measurements as well.
v7: - fix fdt_test_chosen to not expect kaslr-seed for CONFIG_MEASURED_BOOT and CONFIG_ARMV8_SEC_FIRMWARE_SUPPORT v6: - collected tags - add patch to fdt ut v5: - fixed typo in commit message s/it's/its/ - use cmd_process_error per Michal's suggestion - split into separate patches - remove the rng device index noting it as a future enhancement v4: - add missing /n to notice in kaslrseed cmd - combine ints in declaration - remove unused vars from board/xilinx/common/board.c ft_board_setup v3: - skip if CONFIG_MEASURED_BOOT - fix skip for CONFIG_ARMV8_SEC_FIRMWARE_SUPPORT - pass in rng index and bool to specify overwrite - remove duplicate error strings printed outside of fdt_kaslrseed - added note to commit log about how EFI STUB weeds out kalsr-seed v2: - fix typo in commit msg - use stack for seed to avoid unecessary malloc/free - move to a library function and deduplicate code by using it elsewhere
Tim Harvey (4): Add fdt_kaslrseed function to add kaslr-seed to chosen node fdt: automatically add /chosen/kaslr-seed if DM_RNG is enabled use fdt_kaslrseed function to de-duplicate code test: cmd: fdt: fix chosen test for DM_RNG
board/xilinx/common/board.c | 40 ---------------------------- boot/fdt_support.c | 53 +++++++++++++++++++++++++++++++++++++ boot/pxe_utils.c | 34 +----------------------- cmd/kaslrseed.c | 49 +++++----------------------------- include/fdt_support.h | 10 +++++++ test/cmd/fdt.c | 8 ++++++ 6 files changed, 79 insertions(+), 115 deletions(-)