Re: [RFC PATCH 1/2] grep: fallback to interpreter if JIT fails with pcre1

[Carlo Arenas <carenas@gmail.com>]

On Sun, Dec 9, 2018 at 4:42 PM brian m. carlson
<sandals@crustytoothpaste.net> wrote:
>
> On Mon, Dec 10, 2018 at 12:51:01AM +0100, Ævar Arnfjörð Bjarmason wrote:
> > Obviously this & what you have in 2/2 needs to be fixed in some way.
> >
> > Is the issue on SELinux, OpenBSD, NetBSD etc. *how* PCRE is creating the
> > the JIT'd code? I.e. presumably Google Chrome's JIT engine, Java JIT and
> > the like work on those setup, or not? I.e. is this something upstream
> > can/is likely to fix eventually?
>
> From the cover letter (but without testing), it seems like it would
> probably be fine to first map the pages read-write to write the code and
> then, once that's done, to map them read-executable. I know JIT
> compilation does work on the BSDs, so presumably that's the technique to
> make it do so.

and that has been implemented (sljitProtExecAllocator.c) as part of the work
triggered by the bug I linked about [1], deep inside sljit (which is
what pcre uses for JIT)

the code AS-IS wouldn't compile for the BSD[2] but that is easy to fix
and sure works as expected but I am under the impression that is not
something that can be considered as a solution as explained by the open issues
described with crashes after a fork()

note that changing the map from read-write to executable will be
prevented by the
same policy so you have to create 2 maps (and therefore a backing file) and I
don't think there is a way to solve that in a foolproof way in a
library which is why
I mentioned more work might be needed to define the right interfaces
so it can be
solved by the application, and that is unlikely to happen with the old library.

Carlo

[1] https://bugs.exim.org/show_bug.cgi?id=1749
[2] https://bugs.exim.org/show_bug.cgi?id=2155