Merge patch series "automatically add /chosen/kaslr-seed and deduplicate code"
Tim Harvey <tharvey@gateworks.com> says:
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.