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From: Kristen Carlson Accardi <kristen@linux.intel.com>
To: Kees Cook <keescook@chromium.org>, Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,  Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>
Subject: Re: [RFC PATCH 08/11] x86: Add support for finer grained KASLR
Date: Thu, 06 Feb 2020 09:36:59 -0800
Message-ID: <c9946c229f6f53379deeef00fbdee88fe2fdd96e.camel@linux.intel.com> (raw)
In-Reply-To: <202002060353.A6A064A@keescook>

On Thu, 2020-02-06 at 03:56 -0800, Kees Cook wrote:
> On Wed, Feb 05, 2020 at 05:17:11PM -0800, Andy Lutomirski wrote:
> > On Wed, Feb 5, 2020 at 2:39 PM Kristen Carlson Accardi
> > <kristen@linux.intel.com> wrote:
> > > At boot time, find all the function sections that have separate
> > > .text
> > > sections, shuffle them, and then copy them to new locations.
> > > Adjust
> > > any relocations accordingly.
> > > 
> > > +       sort(base, num_syms, sizeof(int), kallsyms_cmp,
> > > kallsyms_swp);
> > 
> > Hah, here's a huge bottleneck.  Unless you are severely
> > memory-constrained, never do a sort with an expensive swap function
> > like this.  Instead allocate an array of indices that starts out as
> > [0, 1, 2, ...].  Sort *that* where the swap function just swaps the
> > indices.  Then use the sorted list of indices to permute the actual
> > data.  The result is exactly one expensive swap per item instead of
> > one expensive swap per swap.
> 
> I think there are few places where memory-vs-speed need to be
> examined.
> I remain surprised about how much memory the entire series already
> uses
> (58MB in my local tests), but I suspect this is likely dominated by
> the
> two factors: a full copy of the decompressed kernel, and that the
> "allocator" in the image doesn't really implement free():
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/decompress/mm.h#n55
> 

Yes - that was a huge issue (that free() doesn't actually...). Having
to do the copy really caused me to need to bump up the boot heap.
Thankfully, this is a readily solvable problem.

I think there's a temptation to focus too hard on the boot latency.
While I measured this on a reasonably fast system, we aren't talking
minutes of latency here, just a second or a second and a half. I know
there are those who sweat the milliseconds on booting vms, but I expect
they might just turn this feature off anyway. That said, there are
absolutely a lot of great ideas for improving things here that I am
excited to try should people be interested enough in this feature for
me to take it to the next stage.




  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
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 [this message]
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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