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

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Message-ID: <20190426180235.GC9835@mit.edu>
Date:   Fri, 26 Apr 2019 14:02:35 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     "Reshetova, Elena" <elena.reshetova@...el.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        David Laight <David.Laight@...lab.com>,
        Ingo Molnar <mingo@...nel.org>,
        "'Peter Zijlstra'" <peterz@...radead.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "luto@...nel.org" <luto@...nel.org>,
        "luto@...capital.net" <luto@...capital.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>
Subject: Re: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

On Fri, Apr 26, 2019 at 10:44:20AM -0700, Eric Biggers wrote:
> Would it be possibly to call ChaCha20 through the actual crypto API so that SIMD
> instructions (e.g. AVX-2) could be used?  That would make it *much* faster.
> Also consider AES-CTR with AES-NI instructions.

It's not obvious SIMD instructions will be faster in practice, since
it requires saving and restoring the vector/FPU registers.  If you're
going to be doing a *lot* of vector processing (for example when doing
block-level RAID-5 / RAID-6 computations), it might be worth it.  But
if you're only going to be turning the crank for 12 or 20 rounds, the
overhead of calling kernel_fpu_begin() and kernel_fpu_end() is
probably going to make this worth it.

As far as using aesni (if available) is concerned, since we don't need
to worry about interoperability between two systems ala IPSEC, it's
definitely something that's worth investigating.

       	    	       		 	      - Ted