Skip to content
Commit 049f9ae9 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld
Browse files

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 <tytso@mit.edu>
Suggested-by: default avatarH. Peter Anvin <hpa@zytor.com>
Suggested-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
parent 9592eef7
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment