fdt: add support for rng-seed
Introducing a chosen node, rng-seed, which is an entropy that can be
passed to kernel called very early to increase initial device
randomness. Bootloader should provide this entropy and the value is
read from /chosen/rng-seed in DT.
Obtain of_fdt_crc32 for CRC check after early_init_dt_scan_nodes(),
since early_init_dt_scan_chosen() would modify fdt to erase rng-seed.
Add a new interface add_bootloader_randomness() for rng-seed use case.
Depends on whether the seed is trustworthy, rng seed would be passed to
add_hwgenerator_randomness(). Otherwise it would be passed to
add_device_randomness(). Decision is controlled by kernel config
RANDOM_TRUST_BOOTLOADER.
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu> # drivers/char/random.c
Signed-off-by: Will Deacon <will@kernel.org>
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 3e86688..2794f4b 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -573,3 +573,12 @@
has not installed a hidden back door to compromise the CPU's
random number generation facilities. This can also be configured
at boot with "random.trust_cpu=on/off".
+
+config RANDOM_TRUST_BOOTLOADER
+ bool "Trust the bootloader to initialize Linux's CRNG"
+ help
+ Some bootloaders can provide entropy to increase the kernel's initial
+ device randomness. Say Y here to assume the entropy provided by the
+ booloader is trustworthy so it will be added to the kernel's entropy
+ pool. Otherwise, say N here so it will be regarded as device input that
+ only mixes the entropy pool.
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