[PATCH v5sub3 4/4] arm64: efi: invoke EFI_RNG_PROTOCOL to supply KASLR randomness

On Wed, 10 Feb, at 06:55:05PM, Ard Biesheuvel wrote:

Since arm64 does not use a decompressor that supplies an execution
environment where it is feasible to some extent to provide a source of
randomness, the arm64 KASLR kernel depends on the bootloader to supply
some random bits in the /chosen/kaslr-seed DT property upon kernel entry.

On UEFI systems, we can use the EFI_RNG_PROTOCOL, if supplied, to obtain
some random bits. At the same time, use it to randomize the offset of the
kernel Image in physical memory.

Signed-off-by: Ard Biesheuvel <redacted>
---
 arch/arm64/Kconfig                        |  5 ++
 drivers/firmware/efi/libstub/arm-stub.c   | 40 ++++++----
 drivers/firmware/efi/libstub/arm64-stub.c | 78 ++++++++++++++------
 drivers/firmware/efi/libstub/fdt.c        | 14 ++++
 4 files changed, 102 insertions(+), 35 deletions(-)

Reviewed-by: Matt Fleming <redacted>