Linear Address Spaces: Unsafe at any speed [article]

By: dmcq (dmcq.delete@this.fano.co.uk), June 30, 2022 10:20 am
Room: Moderated Discussions
Brendan (btrotter.delete@this.gmail.com) on June 30, 2022 11:09 am wrote:
> Hi,
>
> Kester L (nobody.delete@this.nothing.com) on June 29, 2022 1:49 pm wrote:
> > https://queue.acm.org/detail.cfm?id=3534854
> >
> >

> > The linear address space as a concept is unsafe at any speed, and it badly needs mandatory CHERI
> > seat belts. But even better would be to get rid of linear address spaces entirely and go back to
> > the future, as successfully implemented in the Rational R1000 computer 30-plus years ago.
> >

> >
> > Your thoughts on this article? I was under the impression that a lot of the 80s attempts
> > at capability machines (or really, anything that wasn't trying to be a glorified PDP-11)
> > floundered because of performance and cost issues (i.e. the Intel i432).
>
> My thoughts on the article itself is that it has a strong "marketing" smell. Let's
> ignore the article's words and focus on the "safety vs. performance" question.
>
> You can split it into 2 very different problems:
>
> a) Reducing the amount of developer effort required to create correct and efficient software
>
> b) Maximizing the efficiency (performance per watt per $) for normal
> users (not software developers) executing correct software
>
> For the former, the latter is mostly irrelevant. E.g. if you're running a specially instrumented
> "debug version" (with lots of extra checks enabled) in a special environment (e.g. under valgrind)
> and its 200 times slower, most developers simply won't have a reason to care.
>
> For the latter, the former is mostly irrelevant. The only thing you actually care about is protecting
> everything (kernel, other processes) from untrusted (potentially deliberately malicious) code;
> and for this you only care about the boundaries between "inside the process" and "outside the
> process" (and you do not care about anything inside the process trashing anything else in the
> process). For modern systems this is invariably done with paravirtualization - a process runs
> inside its own virtual machine (with virtual memory, virtual CPUs/threads, highly abstracted virtual
> IO like "open()" and "write()" instead of anything resembling physical devices).
>
> You can't/shouldn't combine these problems; because as soon as you do you're forcing a compromise (worse
> safety for the former and/or worse efficiency for the latter). Anyone who doesn't seem to understand this
> (e.g. CHERI designers) are trying to solve a problem without understanding the nature of the problem.
>
> However; there is some overlap. Good software developers try to create correct and efficient software (and
> not just correct software). Anything intended to reduce the effort needed to create correct and efficient
> software should/must be able to handle all the tricks that could be used to improve the efficiency of correct
> code. This includes using raw assembly language for highly specialized pieces; and self-modifying code and
> run-time code generation; and improving locality by using a single memory allocation for several objects of
> different types; and improving SIMD performance by using "structure of arrays" instead of "array of structures/objects";
> and recognizing that sometimes the same object has different types in different places (a pointer/reference
> to a structure/object that is used as a raw integer when calculating a hash, a "big integer" in one place
> that is an array of unsigned integers in another place, multiple inheritance, etc).
>
> - Brendan

I think your idea of 'normal users' needs a bit of refining. I'm not sure there's many people left who a company would pay after they're allowed to do the sort of tricks you're talking about. Do you mean ners=ds who are just developing a program for themselves and waste their lives to no profit?
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TopicPosted ByDate
Linear Address Spaces: Unsafe at any speed [article]Kester L2022/06/29 12:49 PM
  Linear Address Spaces: Unsafe at any speed [article]Rayla2022/06/29 01:14 PM
    Linear Address Spaces: Unsafe at any speed [article]Kester L2022/06/29 01:43 PM
      Not just worse-is-betterMark Roulo2022/06/29 02:21 PM
        Not just worse-is-better---2022/06/29 06:07 PM
  Linear Address Spaces: Unsafe at any speed [article]2022/06/29 11:08 PM
    Linear Address Spaces: Unsafe at any speed [article]Groo2022/06/30 11:56 AM
      Linear Address Spaces: Unsafe at any speed [article]Michael S2022/06/30 01:17 PM
  Linear Address Spaces: Unsafe at any speed [article]Eric Fink2022/06/30 12:43 AM
  Linear Address Spaces: Unsafe at any speed [article]dmcq2022/06/30 02:17 AM
  Linear Address Spaces: Unsafe at any speed [article]Adrian2022/06/30 04:36 AM
    Linear Address Spaces: Unsafe at any speed [article]anonymou52022/06/30 06:28 AM
      Linear Address Spaces: Unsafe at any speed [article]Anon42022/06/30 03:37 PM
        Linear Address Spaces: Unsafe at any speed [article]anonymou52022/06/30 05:19 PM
          Linear Address Spaces: Unsafe at any speed [article]dmcq2022/07/01 03:16 AM
            Linear Address Spaces: Unsafe at any speed [article]anonymou52022/07/01 04:40 AM
              Linear Address Spaces: Unsafe at any speed [article]dmcq2022/07/01 05:11 AM
                Linear Address Spaces: Unsafe at any speed [article]anonymou52022/07/01 07:09 AM
              Linear Address Spaces: Unsafe at any speed [article]dmcq2022/07/01 05:11 AM
                Why the duplicates?dmcq2022/07/01 05:18 AM
              Linear Address Spaces: Unsafe at any speed [article]2022/07/01 09:41 PM
    Linear Address Spaces: Unsafe at any speed [article]Foo_2022/06/30 06:43 AM
      Fragmentation: Both Size and LifetimeMark Roulo2022/06/30 07:25 AM
        Fragmentation: Both Size and Lifetime2022/06/30 09:09 AM
          Fragmentation: Both Size and Lifetimedmcq2022/06/30 10:12 AM
          Fragmentation: Both Size and LifetimeBrendan2022/06/30 03:08 PM
            Fragmentation: Both Size and Lifetime2022/07/02 02:12 AM
              Fragmentation: Both Size and LifetimeBrendan2022/07/02 12:56 PM
                Fragmentation: Both Size and Lifetime2022/07/04 04:34 AM
                  Fragmentation: Both Size and LifetimeBrendan2022/07/04 05:33 AM
                    Fragmentation: Both Size and Lifetime2022/07/04 06:35 AM
                      Fragmentation: Both Size and LifetimeBrendan2022/07/04 03:21 PM
                    Atom is just living at the Dunning-Krueger peakHeikki Kultala2022/07/04 08:26 AM
                      Atom is just living at the Dunning-Krueger peak2022/07/04 08:57 AM
      Linear Address Spaces: Unsafe at any speed [article]Adrian2022/06/30 07:31 AM
        Linear Address Spaces: Unsafe at any speed [article]Foo_2022/06/30 08:07 AM
          Linear Address Spaces: Unsafe at any speed [article]Adrian2022/06/30 08:43 AM
            Linear Address Spaces: Unsafe at any speed [article]Foo_2022/07/01 02:21 AM
              Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/01 08:58 PM
                Linear Address Spaces: Unsafe at any speed [article]Foo_2022/07/03 01:45 AM
                  Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/03 09:04 PM
                    Linear Address Spaces: Unsafe at any speed [article]ananon2022/07/04 01:35 AM
                    Linear Address Spaces: Unsafe at any speed [article]Foo_2022/07/04 02:11 AM
                      Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/05 12:36 AM
                    Linear Address Spaces: Unsafe at any speed [article]2022/07/04 03:18 AM
                    Linear Address Spaces: Unsafe at any speed [article]TAG2022/07/04 06:50 AM
                    Linear Address Spaces: Unsafe at any speed [article]Brendan2022/07/04 03:54 PM
                      Linear Address Spaces: Unsafe at any speed [article]Brendan2022/07/04 04:05 PM
                      Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/05 01:18 AM
                        Linear Address Spaces: Unsafe at any speed [article]Brendan2022/07/06 04:16 PM
                          Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/06 11:33 PM
        Linear Address Spaces: Unsafe at any speed [article]2022/06/30 09:40 AM
    Linear Address Spaces: Unsafe at any speed [article]---2022/06/30 07:28 AM
      Linear Address Spaces: Unsafe at any speed [article]Michael S2022/06/30 12:00 PM
    Linear Address Spaces: Unsafe at any speed [article]Jörn Engel2022/06/30 04:34 PM
      Linear Address Spaces: Unsafe at any speed [article]Adrian2022/06/30 11:55 PM
        Sorry, typo correctionAdrian2022/07/01 12:04 AM
        Linear Address Spaces: Unsafe at any speed [article]2022/07/01 03:01 AM
          Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/01 10:00 PM
            Linear Address Spaces: Unsafe at any speed [article]rwessel2022/07/02 06:16 AM
        Linear Address Spaces: Unsafe at any speed [article]Jörn Engel2022/07/01 08:40 AM
          Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/01 10:15 PM
  Linear Address Spaces: Unsafe at any speed [article]Brendan2022/06/30 10:09 AM
    Linear Address Spaces: Unsafe at any speed [article]dmcq2022/06/30 10:20 AM
      Linear Address Spaces: Unsafe at any speed [article]Brendan2022/06/30 02:52 PM
        Linear Address Spaces: Unsafe at any speed [article]dmcq2022/07/01 05:06 AM
          Linear Address Spaces: Unsafe at any speed [article]Brendan2022/07/01 12:24 PM
            Linear Address Spaces: Unsafe at any speed [article]rwessel2022/07/01 07:55 PM
  Linear Address Spaces - Free lunch?Björn Ragnar Björnsson2022/07/02 05:44 PM
    Linear Address Spaces - Free lunch?dmcq2022/07/03 03:30 AM
      Linear Address Spaces - Free lunch?Björn Ragnar Björnsson2022/07/03 03:50 PM
  Linear Address Spaces: Unsafe at any speed [article]Paul A. Clayton2022/07/18 06:49 AM
    Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/18 09:21 AM
      Linear Address Spaces: Unsafe at any speed [article]Brendan2022/07/18 02:11 PM
        Linear Address Spaces: Unsafe at any speed [article]anon22022/07/18 03:54 PM
          Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/18 09:22 PM
            Linear Address Spaces: Unsafe at any speed [article]Michael S2022/07/19 12:00 AM
              Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/19 04:50 AM
        Linear Address Spaces: Unsafe at any speed [article]Adrian2022/07/18 10:02 PM
          Linear Address Spaces: Unsafe at any speed [article]Brendan2022/07/19 07:29 PM
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