Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION

From	Mark Rutland <mark.rutland@arm.com>
Newsgroups	linux.kernel
Subject	Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION
Date	2017-02-07 12:20 +0100
Message-ID	<t8bYt-27Z-3@gated-at.bofh.it> (permalink)
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On Tue, Feb 07, 2017 at 09:34:05AM +0100, Peter Zijlstra wrote:
> On Mon, Feb 06, 2017 at 08:54:38AM -0800, Kees Cook wrote:
> > >
> > > Like I wrote, ideally we'd end up using something like the x86 exception
> > > table with a custom handler. Just no idea how to pull that off without
> > > doing a full blown arch specific implementation, so I didn't go there
> > > quite yet.
> > 
> > I haven't spent much time looking at the extable stuff. (Though
> > coincidentally, I was poking at it for x86's test_nx stuff...) I
> > thought there was a way to build arch-agnostic extables already?
> > kernel/extable.c is unconditionally built-in, for example.
> 
> That doesn't seem to be of much use. It only contains section sort and
> search functions.
> 
> Another problem for generic code would be to figure out what register
> the relevant variable would live in at the time of exception. Here its
> 'obviously' EAX because that's what cmpxchg requires, but in generic
> you'd need a means of querying GCC's register allocator at the exception
> point and somehow using that information for the generation of the
> exception handler.

I think we only need two arch-specific primitives:
(a) mangle a GCC assigned register into an idx stored in the extable
(b) take said index, and grab the relevant register from pt_regs

Then you can have a BUG_VALUE(v, ...), where we use an input "r" (val),
and mangle that into the idx in the extable. In the common case, I'd
hope GCC would leave the register in-place from the cmpxchg.

... or have I misundertood? :)

Thanks,
Mark.

Thread

[PATCH 0/4] refcount_t followups... Kees Cook <keescook@chromium.org> - 2017-02-04 00:30 +0100
  [PATCH 2/4] lkdtm: convert to refcount_t testing Kees Cook <keescook@chromium.org> - 2017-02-04 00:30 +0100
    [tip:locking/core] lkdtm: Convert to refcount_t testing tip-bot for Kees Cook <tipbot@zytor.com> - 2017-02-10 09:50 +0100
  [PATCH 3/4] bug: Switch data corruption check to __must_check Kees Cook <keescook@chromium.org> - 2017-02-04 00:30 +0100
  [PATCH 1/4] refcount_t: fix Kconfig help Kees Cook <keescook@chromium.org> - 2017-02-04 00:30 +0100
  [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION Kees Cook <keescook@chromium.org> - 2017-02-04 00:30 +0100
    Re: [PATCH 4/4] refcount: Report failures through  CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-05 16:50 +0100
      Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION Kees Cook <keescook@chromium.org> - 2017-02-06 00:40 +0100
        Re: [PATCH 4/4] refcount: Report failures through  CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-06 10:00 +0100
          Re: [PATCH 4/4] refcount: Report failures through CHECK_DATA_CORRUPTION Kees Cook <keescook@chromium.org> - 2017-02-06 18:00 +0100
            Re: [PATCH 4/4] refcount: Report failures through  CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-07 09:40 +0100
              Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Mark Rutland <mark.rutland@arm.com> - 2017-02-07 12:20 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-07 13:40 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Mark Rutland <mark.rutland@arm.com> - 2017-02-07 15:00 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-07 16:10 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Mark Rutland <mark.rutland@arm.com> - 2017-02-07 17:10 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-07 18:40 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Mark Rutland <mark.rutland@arm.com> - 2017-02-07 19:00 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-08 10:20 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-08 10:50 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Mark Rutland <mark.rutland@arm.com> - 2017-02-08 16:00 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Kees Cook <keescook@chromium.org> - 2017-02-08 22:30 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Peter Zijlstra <peterz@infradead.org> - 2017-02-09 11:30 +0100
                Re: [kernel-hardening] Re: [PATCH 4/4] refcount: Report failures  through CHECK_DATA_CORRUPTION Kees Cook <keescook@chromium.org> - 2017-02-11 00:40 +0100

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