Re: [PATCH v3] init: Fix false positives in W+X checking

[Jeffrey Hugo]

On 4/30/2018 12:40 PM, Kees Cook wrote:
> On Mon, Apr 30, 2018 at 10:19 AM, Laura Abbott <labbott@xxxxxxxxxx> wrote:
> > On 04/30/2018 08:59 AM, Jeffrey Hugo wrote:
> > > load_module() creates W+X mappings via __vmalloc_node_range() (from
> > > layout_and_allocate()->move_module()->module_alloc()) by using
> > > PAGE_KERNEL_EXEC.  These mappings are later cleaned up via
> > > "call_rcu_sched(&freeinit->rcu, do_free_init)" from do_init_module().
> > >
> > > This is a problem because call_rcu_sched() queues work, which can be run
> > > after debug_checkwx() is run, resulting in a race condition.  If hit, the
> > > race results in a nasty splat about insecure W+X mappings, which results
> > > in a poor user experience as these are not the mappings that
> > > debug_checkwx() is intended to catch.
> > >
> > > This issue is observed on multiple arm64 platforms, and has been
> > > artificially triggered on an x86 platform.
> > >
> > > Address the race by flushing the queued work before running the
> > > arch-defined mark_rodata_ro() which then calls debug_checkwx().
> > >
> > > Reported-by: Timur Tabi <timur@xxxxxxxxxxxxxx>
> > > Reported-by: Jan Glauber <jan.glauber@xxxxxxxxxxxxxxxxxx>
> > > Fixes: e1a58320a38d ("x86/mm: Warn on W^X mappings")
> > > Signed-off-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>
> > > Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
> > > Acked-by: Will Deacon <will.deacon@xxxxxxx>
> > > ---
> >
> > Acked-by: Laura Abbott <labbott@xxxxxxxxxx>
> >
> > If you don't have a tree for this to go through, I might suggest having
> > Kees take it.
>
> akpm has taken the W^X stuff in the past, but I'm happy to do so. Just
> let me know either way. :)
>
> -Kees

That sounds fine to me.  Is that agreeable to you, Andrew?

--
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
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