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Re: [PATCH v2 1/4] init: create cmdline param to disable readonly

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On Mon, Nov 30, 2015 at 01:52:10PM -0800, Kees Cook wrote:
> On Wed, Nov 25, 2015 at 11:51 PM, Ingo Molnar <mingo@kernel.org> wrote:
> > * Kees Cook <keescook@chromium.org> wrote:
> >> +#ifdef CONFIG_DEBUG_RODATA
> >
> > Btw., could you please remove the Kconfig option altogether in an additional patch
> > and make read-only sections an always-on feature? It has been default-y for years
> > and all distros have it enabled.
> 
> Yeah, this is something I've wanted to do for a while, but I would
> point out that only a few architectures have actually implemented it,
> and for arm and arm64 it was very recent:

I don't think it can entirely be a kernel command line option.  On ARM,
enabling DEBUG_RODATA has a substantial effect on the size of the kernel
image - we have to pad various sections to 1MB boundaries so we can
set the appropriate permissions.

Forcing this layout on everyone won't work.

What we can do is the half-way house: we can have the kernel command
line option which enables and disables the protections, but the layout
of the kernel image would still need to be controlled by DEBUG_RODATA.
I'm left wondering what the advantage of that would be: it'd end up
offering a suboptimal layout, additional memory usage but without the
benefits of memory protections.

The alternative is keeping the kernel in unlinked object form, and
laying out and linking the kernel at boot time, probably in PIC
assembly code.  That's possible but I think is undesirable.

So all in all, I'm in favour of keeping things as they are on ARM.

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[PATCH v2 0/4] introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-26 00:40 +0100
  [PATCH v2 1/4] init: create cmdline param to disable readonly Kees Cook <keescook@chromium.org> - 2015-11-26 00:40 +0100
    Re: [PATCH v2 1/4] init: create cmdline param to disable readonly "PaX Team" <pageexec@freemail.hu> - 2015-11-26 01:40 +0100
    Re: [kernel-hardening] [PATCH v2 1/4] init: create cmdline param to  disable readonly Greg KH <greg@kroah.com> - 2015-11-26 02:10 +0100
    Re: [PATCH v2 1/4] init: create cmdline param to disable readonly Ingo Molnar <mingo@kernel.org> - 2015-11-26 09:00 +0100
      Re: [PATCH v2 1/4] init: create cmdline param to disable readonly Kees Cook <keescook@chromium.org> - 2015-11-30 23:00 +0100
        Re: [PATCH v2 1/4] init: create cmdline param to disable readonly Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-11-30 23:30 +0100
          Re: [PATCH v2 1/4] init: create cmdline param to disable readonly Kees Cook <keescook@chromium.org> - 2015-11-30 23:40 +0100
          Re: [PATCH v2 1/4] init: create cmdline param to disable readonly Ingo Molnar <mingo@kernel.org> - 2015-12-01 08:30 +0100
        Re: [PATCH v2 1/4] init: create cmdline param to disable readonly Heiko Carstens <heiko.carstens@de.ibm.com> - 2015-12-01 08:20 +0100
  [PATCH v2 3/4] lkdtm: verify that __ro_after_init works correctly Kees Cook <keescook@chromium.org> - 2015-11-26 00:40 +0100
  [PATCH v2 2/4] introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-11-26 00:40 +0100
    Re: [PATCH v2 2/4] introduce post-init read-only memory "PaX Team" <pageexec@freemail.hu> - 2015-11-26 01:20 +0100
      Re: [PATCH v2 2/4] introduce post-init read-only memory "H. Peter Anvin" <hpa@zytor.com> - 2015-11-30 23:30 +0100
        Re: [PATCH v2 2/4] introduce post-init read-only memory Kees Cook <keescook@chromium.org> - 2015-12-09 20:40 +0100
  [PATCH v2 4/4] x86, vdso: mark vDSO read-only after init Kees Cook <keescook@chromium.org> - 2015-11-26 00:40 +0100

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