From: Jason A. Donenfeld Date: Wed, 23 Mar 2022 03:43:12 +0000 (-0600) Subject: random: treat bootloader trust toggle the same way as cpu trust toggle X-Git-Tag: v4.19.249~111 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=2c946656444357c5723743379e67c96576cb0e14;p=thirdparty%2Fkernel%2Fstable.git random: treat bootloader trust toggle the same way as cpu trust toggle commit d97c68d178fbf8aaaf21b69b446f2dfb13909316 upstream. 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: Theodore Ts'o Cc: Graham Christensen Reviewed-by: Ard Biesheuvel Reviewed-by: Dominik Brodowski Link: https://github.com/NixOS/nixpkgs/pull/165355 Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 1dea3d23fc4ca..500032af01927 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3697,6 +3697,12 @@ fully seed the kernel's CRNG. Default is controlled by CONFIG_RANDOM_TRUST_CPU. + random.trust_bootloader={on,off} + [KNL] Enable or disable trusting the use of a + seed passed by the bootloader (if available) to + fully seed the kernel's CRNG. Default is controlled + by CONFIG_RANDOM_TRUST_BOOTLOADER. + ras=option[,option,...] [KNL] RAS-specific options cec_disable [X86] diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig index 3bc53a8c93fec..094548183f8b0 100644 --- a/drivers/char/Kconfig +++ b/drivers/char/Kconfig @@ -576,4 +576,5 @@ config RANDOM_TRUST_BOOTLOADER 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. \ No newline at end of file + only mixes the entropy pool. This can also be configured at boot with + "random.trust_bootloader=on/off". diff --git a/drivers/char/random.c b/drivers/char/random.c index 19697cc148b7d..5672e6f9b65a5 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -940,11 +940,17 @@ static bool drain_entropy(void *buf, size_t nbytes) **********************************************************************/ 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 @@ -1152,7 +1158,7 @@ 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);