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From: Kristen Carlson Accardi <kristen@linux.intel.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com,  arjan@linux.intel.com, keescook@chromium.org,
	rick.p.edgecombe@intel.com,  x86@kernel.org,
	linux-kernel@vger.kernel.org,
	 kernel-hardening@lists.openwall.com
Subject: Re: [RFC PATCH 03/11] x86/boot: Allow a "silent" kaslr random byte fetch
Date: Thu, 06 Feb 2020 08:58:22 -0800
Message-ID: <2da7c2370b1bd5474ce51a22b04d81e2734232b1.camel@linux.intel.com> (raw)
In-Reply-To: <B173D69E-DC6C-4658-B5CB-391D3C6A6597@amacapital.net>

On Wed, 2020-02-05 at 17:08 -0800, Andy Lutomirski wrote:
> > On Feb 5, 2020, at 2:39 PM, Kristen Carlson Accardi <
> > kristen@linux.intel.com> wrote:
> > 
> > From: Kees Cook <keescook@chromium.org>
> > 
> > Under earlyprintk, each RNG call produces a debug report line. When
> > shuffling hundreds of functions, this is not useful information
> > (each
> > line is identical and tells us nothing new). Instead, allow for a
> > NULL
> > "purpose" to suppress the debug reporting.
> 
> Have you counted how many RDRAND calls this causes?  RDRAND is
> exceedingly slow on all CPUs I’ve looked at. The whole “RDRAND has
> great bandwidth” marketing BS actually means that it has decent
> bandwidth if all CPUs hammer it at the same time. The latency is
> abysmal.  I have asked Intel to improve this, but the latency of that
> request will be quadrillions of cycles :)
> 
> It wouldn’t shock me if just the RDRAND calls account for a
> respectable fraction of total time. The RDTSC fallback, on the other
> hand, may be so predictable as to be useless.

I think at the moment the calls to rdrand are really not the largest
contributor to the latency. The relocations are the real bottleneck -
each address must be inspected to see if it is in the list of function
sections that have been randomized, and the value at that address must
also be inspected to see if it's in the list of function sections.
That's a lot of lookups. That said, I tried to measure the difference
between using Kees' prng vs. the rdrand calls and found little to no
measurable difference. I think at this point it's in the noise -
hopefully we will get to a point where this matters more.

> 
> I would suggest adding a little ChaCha20 DRBG or similar to the KASLR
> environment instead. What crypto primitives are available there?

I will read up on this.



  parent reply index

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-05 22:39 [RFC PATCH 00/11] Finer grained kernel address space randomization Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 01/11] modpost: Support >64K sections Kristen Carlson Accardi
2020-02-06 12:38   ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 02/11] x86: tools/relocs: Support >64K section headers Kristen Carlson Accardi
2020-02-06 12:39   ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 03/11] x86/boot: Allow a "silent" kaslr random byte fetch Kristen Carlson Accardi
2020-02-06  1:08   ` Andy Lutomirski
2020-02-06 11:48     ` Kees Cook
2020-02-06 16:58     ` Kristen Carlson Accardi [this message]
2020-02-05 22:39 ` [RFC PATCH 04/11] x86/boot/KASLR: Introduce PRNG for faster shuffling Kristen Carlson Accardi
2020-02-06  1:11   ` Andy Lutomirski
2020-02-06 15:10   ` Jason A. Donenfeld
2020-02-07  7:23     ` Jean-Philippe Aumasson
2020-02-07  9:05       ` Kees Cook
2020-02-07 16:52         ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 05/11] x86: Makefile: Add build and config option for CONFIG_FG_KASLR Kristen Carlson Accardi
2020-02-06 10:30   ` Peter Zijlstra
2020-02-06 11:52     ` Kees Cook
2020-02-25 17:55   ` Arvind Sankar
2020-02-26 19:13     ` Kristen Carlson Accardi
2020-03-24 21:24     ` Kristen Carlson Accardi
2020-03-25 15:34       ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 06/11] x86: make sure _etext includes function sections Kristen Carlson Accardi
2020-02-06 12:26   ` Kees Cook
2020-02-06 13:15     ` Jann Horn
2020-02-06 16:27       ` David Laight
2020-02-06 14:39     ` Arvind Sankar
2020-02-06 15:29       ` Arvind Sankar
2020-02-06 16:11         ` Andy Lutomirski
2020-02-06 14:57     ` Arvind Sankar
2020-02-06 15:45       ` Arvind Sankar
2020-02-06 19:41     ` Kristen Carlson Accardi
2020-02-06 20:02       ` Andy Lutomirski
2020-02-07  9:24         ` Peter Zijlstra
2020-02-10  1:43           ` Kees Cook
2020-02-10 10:51             ` Peter Zijlstra
2020-02-10 15:54               ` Arjan van de Ven
2020-02-10 16:36                 ` Arvind Sankar
2020-02-21 19:50                   ` Josh Poimboeuf
2020-02-21 23:05                     ` Arvind Sankar
2020-02-05 22:39 ` [RFC PATCH 07/11] x86/tools: Adding relative relocs for randomized functions Kristen Carlson Accardi
2020-02-06 12:37   ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 08/11] x86: Add support for finer grained KASLR Kristen Carlson Accardi
2020-02-06  1:17   ` Andy Lutomirski
2020-02-06 11:56     ` Kees Cook
2020-02-06 17:36       ` Kristen Carlson Accardi
2020-02-06 10:38   ` Peter Zijlstra
2020-02-06 12:06     ` Kees Cook
2020-02-06 14:52       ` Peter Zijlstra
2020-02-06 17:25         ` Kristen Carlson Accardi
2020-02-06 17:35           ` Peter Zijlstra
2020-02-06 17:43             ` Kristen Carlson Accardi
2020-02-25 17:49   ` Arvind Sankar
2020-02-26 19:26     ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 09/11] kallsyms: hide layout and expose seed Kristen Carlson Accardi
2020-02-06 12:32   ` Kees Cook
2020-02-06 17:51     ` Kristen Carlson Accardi
2020-02-06 19:27       ` Jann Horn
2020-03-02 19:01         ` Kristen Carlson Accardi
2020-03-02 19:08           ` Kees Cook
2020-03-02 19:19             ` Kristen Carlson Accardi
2020-02-27  2:42       ` Baoquan He
2020-02-27 16:02         ` Kees Cook
2020-02-28  3:36           ` Baoquan He
2020-02-05 22:39 ` [RFC PATCH 10/11] module: Reorder functions Kristen Carlson Accardi
2020-02-06 12:41   ` Kees Cook
2020-02-11 12:39     ` Jessica Yu
2020-02-05 22:39 ` [RFC PATCH 11/11] x86/boot: Move "boot heap" out of .bss Kristen Carlson Accardi
2020-02-06  0:11   ` Arvind Sankar
2020-02-06  0:33     ` Kristen Carlson Accardi
2020-02-06 11:13     ` Kees Cook
2020-02-06 14:25       ` Arvind Sankar
2020-02-06 21:32         ` Kees Cook

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