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Re: regarding the changes to kernel entropy gathering
On Sun, Apr 04, 2021 at 11:14:31AM -0700, John Nemeth wrote:
> I understand the need for good random sources, and won't argue
> it. My question is, how can we tell what random sources a system
> actually has, i.e. is there some flag that cpuctl identify shows
> when a system has RDRAND/RDSEED? Are there other sources that can
> be positively identified as providing randomness?
I am not sure I understand the question correctly. rndctl will show the
entropy available from the source. For cpu internal random sources,
on x86 cpuctl identify shows them:
# cpuctl identify 0 | fgrep RDRAND
cpu0: features1 0x7ffafbff<F16C,RDRAND>
# cpuctl identify 0 | fgrep RDSEED
cpu0: features5 0x29c6fbf<INVPCID,RTM,FPUCSDS,MPX,RDSEED,ADX,SMAP,CLFLUSHOPT>
# rndctl -l
Source Bits Type Flags
[..]
system-power 0 power estimate, collect, v, t, dt
autoconf 0 ??? estimate, collect, t
seed 256 ??? estimate, collect, v
rdrand/rdseed 512 rng estimate, collect, v
or on a system with another cpu:
# rndctl -l
Source Bits Type Flags
[..]
ualea0 512 rng estimate, collect, v
[..]
system-power 0 power estimate, collect, v, t, dt
autoconf 0 ??? estimate, collect, t
seed 256 ??? estimate, collect, v
and yet another with no trusted source, but properly seeded (also an
old and non-x86 system):
# rndctl -l
Source Bits Type Flags
/dev/random 0 ??? estimate, collect, v
ucom7 0 tty estimate, collect, v, t, dt
ucom6 0 tty estimate, collect, v, t, dt
ucom5 0 tty estimate, collect, v, t, dt
ucom4 0 tty estimate, collect, v, t, dt
ucom3 0 tty estimate, collect, v, t, dt
ucom2 0 tty estimate, collect, v, t, dt
ucom1 0 tty estimate, collect, v, t, dt
ucom0 0 tty estimate, collect, v, t, dt
sd1 0 disk estimate, collect, v, t, dt
sd0 0 disk estimate, collect, v, t, dt
cpu0 0 vm estimate, collect, v, t, dv
hardclock 0 skew estimate, collect, t
mvgbe0 0 net estimate, v, t, dt
system-power 0 power estimate, collect, v, t, dt
autoconf 0 ??? estimate, collect, t
seed 256 ??? estimate, collect, v
Martin
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