linux-kernel - Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

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Message-ID: <201905291136.FD61FF42@keescook>
Date:   Wed, 29 May 2019 11:37:17 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
Cc:     Theodore Ts'o <tytso@....edu>, Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Eric Biggers <ebiggers3@...il.com>,
        "ebiggers@...gle.com" <ebiggers@...gle.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "Perla, Enrico" <enrico.perla@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

On Wed, May 29, 2019 at 10:13:43AM +0000, Reshetova, Elena wrote:
> On related note: the current prng we have in kernel (prandom) is based on a
> *very old* style of prngs, which is basically 4 linear LFSRs xored together. 
> Nowadays, we have much more powerful prngs that show much better
> statistical and even security properties (not cryptographically secure, but still
> not so linear like the one above). 
> What is the reason why we still use a prng that is couple of decades away from the
> state of art in the area? It is actively used, especially by network stack,
> should we update it to smth that is more appropriate (speed would be comparable)?
> 
> I am mostly talking about PCG-based generators:
> http://www.pcg-random.org/
> 
> If people are interested, I could put together a PoC and we have an expert here we can
> consult for providing calculations for min-entropy, HILL entropy and whatever 
> is requested. 

If we get better generators with no speed loss, I can't imagine anyone
objecting. :)

-- 
Kees Cook