If CONFIG_RANDOM_TRUST_CPU is set, the RNG initializes using RDRAND. But, the user can disable (or enable) this behavior by setting `random.trust_cpu=0/1` on the kernel command line. This allows system builders to do reasonable things while avoiding howls from tinfoil hatters. (Or vice versa.) CONFIG_RANDOM_TRUST_BOOTLOADER is basically the same thing, but regards the seed passed via EFI or device tree, which might come from RDRAND or a TPM or somewhere else. In order to allow distros to more easily enable this while avoiding those same howls (or vice versa), this commit adds the corresponding `random.trust_bootloader=0/1` toggle. Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> Cc: Theodore Ts'o <tytso@xxxxxxx> Cc: Graham Christensen <graham@xxxxxxxxxxx> Link: https://github.com/NixOS/nixpkgs/pull/165355 Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> --- drivers/char/random.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 7b7f5e6596c2..c8974e5f57e1 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -948,11 +948,17 @@ static bool drain_entropy(void *buf, size_t nbytes, bool force) **********************************************************************/ static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU); +static bool trust_bootloader __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER); static int __init parse_trust_cpu(char *arg) { return kstrtobool(arg, &trust_cpu); } +static int __init parse_trust_bootloader(char *arg) +{ + return kstrtobool(arg, &trust_bootloader); +} early_param("random.trust_cpu", parse_trust_cpu); +early_param("random.trust_bootloader", parse_trust_bootloader); /* * The first collection of entropy occurs at system boot while interrupts @@ -1160,7 +1166,7 @@ EXPORT_SYMBOL_GPL(add_hwgenerator_randomness); */ void add_bootloader_randomness(const void *buf, size_t size) { - if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER)) + if (trust_bootloader) add_hwgenerator_randomness(buf, size, size * 8); else add_device_randomness(buf, size); -- 2.35.1
