Re: [kernel-hardening] Re: [PATCH 1/2] x86: introduce post-init read-only memory

From	Kees Cook <keescook@chromium.org>
Newsgroups	linux.kernel
Subject	Re: [kernel-hardening] Re: [PATCH 1/2] x86: introduce post-init read-only memory
Date	2015-11-25 16:10 +0100
Message-ID	<qyJRM-7Wr-3@gated-at.bofh.it> (permalink)
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On Tue, Nov 24, 2015 at 4:54 PM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> On Tue, 2015-11-24 at 16:44 -0800, Kees Cook wrote:
>> On Tue, Nov 24, 2015 at 4:34 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> > On Nov 24, 2015 1:38 PM, "Kees Cook" <keescook@chromium.org> wrote:
>> > >
>> > > One of the easiest ways to protect the kernel from attack is to reduce
>> > > the internal attack surface exposed when a "write" flaw is available. By
>> > > making as much of the kernel read-only as possible, we reduce the
>> > > attack surface.
>> > >
>> > > Many things are written to only during __init, and never changed
>> > > again. These cannot be made "const" since the compiler will do the wrong
>> > > thing (we do actually need to write to them). Instead, move these items
>> > > into a memory region that will be made read-only during mark_rodata_ro()
>> > > which happens after all kernel __init code has finished.
>> > >
>> > > This introduces __read_only as a way to mark such memory, and adds some
>> > > documentation about the existing __read_mostly marking.
>> >
>> > Obligatory bikeshed:  __ro_after_init, please.  It's barely longer,
>> > and it directly explains what's going on.  __read_only makes me think
>> > that it's really read-only and could, for example, actually be in ROM.
>>
>> I'm fine with that. Anyone else want to chime in before I send a v2?
>
> I'm not clear on why this is x86 only?

I was initially looking at how __read_mostly got implemented, and it
seemed like section names were done on a per-arch basis. But it
doesn't seem like that needs to be true.

> It looks like it would work on any arch, or is there some toolchain
> requirement?

Given that the other sections are in the common linux.lds.h file, it
seems unlikely to me. I'll try it in an arch-agnostic way and see what
happens. :)

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security
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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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