Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory
Date	2015-11-27 09:10 +0100
Message-ID	<qzmgq-eI-13@gated-at.bofh.it> (permalink)
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* PaX Team <pageexec@freemail.hu> wrote:

> On 26 Nov 2015 at 11:42, Ingo Molnar wrote:
> 
> > * PaX Team <pageexec@freemail.hu> wrote:
> > 
> > > On 26 Nov 2015 at 9:54, Ingo Molnar wrote:
> >
> > > e.g., imagine that the write was to a function pointer (even an entire ops 
> > > structure) or a boolean that controls some important feature for after-init 
> > > code. ignoring/dropping such writes could cause all kinds of logic bugs (if not 
> > > worse).
> > 
> > Well, the typical case is that it's a logic bug to _do_ the write: the structure 
> > was marked readonly for a reason but some init code re-runs during suspend or so.
> 
> that's actually not the typical case in my experience, but rather these two:
> 
> 1. initial mistake: someone didn't actually check whether the given object can
>    be __read_only
> 
> 2. code evolution: an object that was once written by __init code only (and
>    thus proactively subjected to __read_only) gets modified by non-init code
>    due to later changes
> 
> what you described above is a third case where there's a latent bug to begin 
> (unintended write) with that __read_only merely exposes but doesn't create 
> itself, unlike the two cases above (intended writes getting caught by wrong use 
> of __read_only).

You are right, I concede this part of the argument - what you describe is probably 
the most typical way to get ro-faults.

I do maintain the (sub-)argument that oopsing or relying on tooling help years 
down the line is vastly inferior to fixing up the problem and generating a 
one-time stack dump so that kernel developers have a chance to fix the bug. The 
sooner we detect and dump such information the more likely it is that such bugs 
don't get into end user kernel versions.

> my proposal would produce the exact same reports, the difference is in letting 
> the write attempt succeed vs. skipping it. this latter step is what is wrong 
> since it introduces at least a logic bug the same way the constprop optimization 
> created a logic bug.

Yes, you are right and I agree.

Does anyone want to submit such a patch for upstream? Looks like a good change.

Thanks,

	Ingo
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Thread

[PATCH 0/2] introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-24 22:40 +0100
  [PATCH 1/2] x86: introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-24 22:40 +0100
    Re: [PATCH 1/2] x86: introduce post-init read-only memory Andy Lutomirski <luto@amacapital.net> - 2015-11-25 01:40 +0100
      Re: [PATCH 1/2] x86: introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-25 01:50 +0100
        Re: [kernel-hardening] Re: [PATCH 1/2] x86: introduce post-init  read-only memory Michael Ellerman <mpe@ellerman.id.au> - 2015-11-25 02:00 +0100
          Re: [kernel-hardening] Re: [PATCH 1/2] x86: introduce post-init  read-only memory Kees Cook <keescook@chromium.org> - 2015-11-25 16:10 +0100
            Re: [kernel-hardening] Re: [PATCH 1/2] x86: introduce post-init  read-only memory Michael Ellerman <mpe@ellerman.id.au> - 2015-11-26 00:10 +0100
              Re: [kernel-hardening] Re: [PATCH 1/2] x86: introduce post-init  read-only memory Kees Cook <keescook@chromium.org> - 2015-11-26 00:40 +0100
  [PATCH 2/2] x86, vdso: mark vDSO read-only after init Kees Cook <keescook@chromium.org> - 2015-11-24 22:50 +0100
  Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Mathias Krause <minipli@googlemail.com> - 2015-11-25 10:20 +0100
    Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Clemens Ladisch <clemens@ladisch.de> - 2015-11-25 11:10 +0100
      Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory "PaX Team" <pageexec@freemail.hu> - 2015-11-25 12:20 +0100
    Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory "PaX Team" <pageexec@freemail.hu> - 2015-11-25 12:10 +0100
      Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-26 10:00 +0100
        Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory "PaX Team" <pageexec@freemail.hu> - 2015-11-26 11:00 +0100
          Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-26 11:50 +0100
            Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory "PaX Team" <pageexec@freemail.hu> - 2015-11-26 13:20 +0100
              Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-27 09:10 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory "PaX Team" <pageexec@freemail.hu> - 2015-11-27 16:40 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Andy Lutomirski <luto@amacapital.net> - 2015-11-27 17:40 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-29 09:10 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory "PaX Team" <pageexec@freemail.hu> - 2015-11-29 12:20 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-29 16:40 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Mathias Krause <minipli@googlemail.com> - 2015-11-29 19:10 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-30 09:10 +0100
        Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Andy Lutomirski <luto@amacapital.net> - 2015-11-26 17:20 +0100
          Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-27 09:10 +0100
            Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-27 19:10 +0100
            Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-27 19:10 +0100
              Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-27 21:10 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Andy Lutomirski <luto@amacapital.net> - 2015-11-27 21:10 +0100
                Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory Ingo Molnar <mingo@kernel.org> - 2015-11-29 09:10 +0100
    Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-25 18:30 +0100
    Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory "H. Peter Anvin" <hpa@zytor.com> - 2015-11-25 18:40 +0100
      Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-25 20:00 +0100
        Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only  memory "H. Peter Anvin" <hpa@zytor.com> - 2015-11-25 20:10 +0100

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