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Re: [PATCH v2] mm: Allow slab_nomerge to be set at build time

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On Fri 23-06-17 12:20:25, Kees Cook wrote:
> On Fri, Jun 23, 2017 at 7:06 AM, Michal Hocko <mhocko@kernel.org> wrote:
> > On Tue 20-06-17 16:09:11, Kees Cook wrote:
> >> Some hardened environments want to build kernels with slab_nomerge
> >> already set (so that they do not depend on remembering to set the kernel
> >> command line option). This is desired to reduce the risk of kernel heap
> >> overflows being able to overwrite objects from merged caches and changes
> >> the requirements for cache layout control, increasing the difficulty of
> >> these attacks. By keeping caches unmerged, these kinds of exploits can
> >> usually only damage objects in the same cache (though the risk to metadata
> >> exploitation is unchanged).
> >
> > Do we really want to have a dedicated config for each hardening specific
> > kernel command line? I believe we have quite a lot of config options
> > already. Can we rather have a CONFIG_HARDENED_CMD_OPIONS and cover all
> > those defauls there instead?
> 
> There's not been a lot of success with grouped Kconfigs in the past
> (e.g. CONFIG_EXPERIMENTAL), but one thing that has been suggested is a
> defconfig-like make target that would collect all the things together.

Which wouldn't reduce the number of config options, would it? I don't
know but is there any usecase when somebody wants to have hardened
kernel and still want to have different defaults than you are
suggesting?
-- 
Michal Hocko
SUSE Labs

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[PATCH v2] mm: Allow slab_nomerge to be set at build time Kees Cook <keescook@chromium.org> - 2017-06-21 01:10 +0200
  Re: [PATCH v2] mm: Allow slab_nomerge to be set at build time Randy Dunlap <rdunlap@infradead.org> - 2017-06-21 01:20 +0200
    Re: [PATCH v2] mm: Allow slab_nomerge to be set at build time Kees Cook <keescook@chromium.org> - 2017-06-21 01:30 +0200
      Re: [PATCH v2] mm: Allow slab_nomerge to be set at build time Randy Dunlap <rdunlap@infradead.org> - 2017-06-21 02:10 +0200
  Re: [PATCH v2] mm: Allow slab_nomerge to be set at build time Michal Hocko <mhocko@kernel.org> - 2017-06-23 16:10 +0200
    Re: [PATCH v2] mm: Allow slab_nomerge to be set at build time Kees Cook <keescook@chromium.org> - 2017-06-23 21:30 +0200
      Re: [PATCH v2] mm: Allow slab_nomerge to be set at build time Michal Hocko <mhocko@kernel.org> - 2017-06-26 11:10 +0200

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