Date: Tue, 24 Feb 2015 12:45:41 -0700 From: Warner Losh <imp@bsdimp.com> To: John-Mark Gurney <jmg@funkthat.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, Harrison Grundy <harrison.grundy@astrodoggroup.com>, freebsd-arch@freebsd.org Subject: Re: locks and kernel randomness... Message-ID: <8157A5FC-C402-4C77-8535-AAF73BB64E8E@bsdimp.com> In-Reply-To: <20150224183051.GJ46794@funkthat.com> References: <20150224012026.GY46794@funkthat.com> <20150224015721.GT74514@kib.kiev.ua> <54EBDC1C.3060007@astrodoggroup.com> <20150224024250.GV74514@kib.kiev.ua> <DD06E2EA-68D6-43D7-AA17-FB230750E55A@bsdimp.com> <20150224174053.GG46794@funkthat.com> <1E4A5E62-6E06-48BA-B5C5-9BD05811CDEF@bsdimp.com> <20150224183051.GJ46794@funkthat.com>
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> On Feb 24, 2015, at 11:30 AM, John-Mark Gurney <jmg@funkthat.com> = wrote: >=20 > Warner Losh wrote this message on Tue, Feb 24, 2015 at 11:03 -0700: >>=20 >>> On Feb 24, 2015, at 10:40 AM, John-Mark Gurney <jmg@funkthat.com> = wrote: >>>=20 >>> Warner Losh wrote this message on Tue, Feb 24, 2015 at 07:56 -0700: >>>> Then again, if you want to change random(), provide a weak_random() = that???s >>>> the traditional non-crypto thing that???s fast and lockless. That = would make it easy >>>> to audit in our tree. The scheduler doesn???t need cryptographic = randomness, it >>>> just needs to make different choices sometimes to ensure its notion = of fairness. >>>=20 >>> I do not support having a weak_random... If the consumer is sure >>> enough that you don't need a secure random, then they can pick an = LCG >>> and implement it themselves and deal (or not) w/ the locking = issues... >>>=20 >>> It appears that the scheduler had an LCG but for some reason the = authors >>> didn't feel like using it here.. >>=20 >> Why don???t you support having a common random routine that???s to = mix the >> pot, but not cryptographically secure? Lots of algorithms use them, = and having >> a common one would keep us from reinventing the wheel. >=20 > Why can't these algorithms use a cryptographically secure RNG instead? > No one has truely answered that point.. Everyone says they want to = use > an insecure RNG, but the real question is, why can't/shouldn't these > algorithms use a CSPRNG? They could, assuming that no locks are needed to get this and the = computation isn=E2=80=99t too large because this is in the fast path of the kernel. = They just don=E2=80=99t need it to be that strong. Not having any other interactions with the rest of = the system is also desirable. Historically, a CSPRNG is spelled rand() or random(). So by calling = those functions, they are saying they want that. Some callers need more, others do not. Warner=
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