[PATCH v5 0/3] automatically add /chosen/kaslr-seed and deduplicate code

[Tom Rini]

On Thu, May 30, 2024 at 03:06:31PM -0700, Tim Harvey wrote:

> 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.

This needs to be reworked / update the test that now breaks:
https://source.denx.de/u-boot/u-boot/-/jobs/849988#L264

-- 
Tom
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