From 049f9ae93d033be6758ad865a9b89650f9f075ec Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Sat, 9 Jul 2022 12:43:06 +0200 Subject: x86/rdrand: Remove "nordrand" flag in favor of "random.trust_cpu" The decision of whether or not to trust RDRAND is controlled by the "random.trust_cpu" boot time parameter or the CONFIG_RANDOM_TRUST_CPU compile time default. The "nordrand" flag was added during the early days of RDRAND, when there were worries that merely using its values could compromise the RNG. However, these days, RDRAND values are not used directly but always go through the RNG's hash function, making "nordrand" no longer useful. Rather, the correct switch is "random.trust_cpu", which not only handles the relevant trust issue directly, but also is general to multiple CPU types, not just x86. However, x86 RDRAND does have a history of being occasionally problematic. Prior, when the kernel would notice something strange, it'd warn in dmesg and suggest enabling "nordrand". We can improve on that by making the test a little bit better and then taking the step of automatically disabling RDRAND if we detect it's problematic. Also disable RDSEED if the RDRAND test fails. Cc: x86@kernel.org Cc: Theodore Ts'o Suggested-by: H. Peter Anvin Suggested-by: Borislav Petkov Acked-by: Borislav Petkov Signed-off-by: Jason A. Donenfeld --- Documentation/admin-guide/kernel-parameters.txt | 5 ----- 1 file changed, 5 deletions(-) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f2d26cb7e853..1e2307f11105 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3733,11 +3733,6 @@ noreplace-smp [X86-32,SMP] Don't replace SMP instructions with UP alternatives - nordrand [X86] Disable kernel use of the RDRAND and - RDSEED instructions even if they are supported - by the processor. RDRAND and RDSEED are still - available to user space applications. - noresume [SWSUSP] Disables resume and restores original swap space. -- cgit v1.2.3