Document the /chosen/kaslr-seed property (and its interaction with the EFI_RNG_PROTOCOL API). Thanks to Ard for clarifications.
Signed-off-by: Kees Cook <[email protected]> Acked-by: Ard Biesheuvel <[email protected]> Acked-by: Mark Rutland <[email protected]> Acked-by: Will Deacon <[email protected]> --- v2: - improved the language a bit based on Ard's notes - added Acks. - (resent to include lists) --- Documentation/devicetree/bindings/chosen.txt | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt index dee3f5d9df26..e3b13ea7d2ae 100644 --- a/Documentation/devicetree/bindings/chosen.txt +++ b/Documentation/devicetree/bindings/chosen.txt @@ -5,9 +5,31 @@ The chosen node does not represent a real device, but serves as a place for passing data between firmware and the operating system, like boot arguments. Data in the chosen node does not represent the hardware. +The following properties are recognized: -stdout-path property --------------------- + +kaslr-seed +----------- + +This property is used when booting with CONFIG_RANDOMIZE_BASE as the +entropy used to randomize the kernel image base address location. Since +it is used directly, this value is intended only for KASLR, and should +not be used for other purposes (as it may leak information about KASLR +offsets). It is parsed as a u64 value, e.g. + +/ { + chosen { + kaslr-seed = <0xfeedbeef 0xc0def00d>; + }; +}; + +Note that if this property is set from UEFI (or a bootloader in EFI +mode) when EFI_RNG_PROTOCOL is supported, it will be overwritten by +the Linux EFI stub (which will populate the property itself, using +EFI_RNG_PROTOCOL). + +stdout-path +----------- Device trees may specify the device to be used for boot console output with a stdout-path property under /chosen, as described in the Devicetree -- 2.7.4 -- Kees Cook Pixel Security
