On Wed, 23 Mar 2022 at 05:11, Jason A. Donenfeld <Jason@xxxxxxxxx> wrote: > > 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> Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > 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 >
