Re: [PATCH 0/2] Fix and re-enable vsyscall=emulate

[Andy Lutomirski]

On Mon, Nov 7, 2011 at 4:33 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> The really nice fix (wiring up access_ok failures to be able to raise
> signals) won't be ready on time for 3.2, so let's try the simpler fix
> for now.

I spoke to hpa about this a couple days ago, and he pointed out a
problem with making access_ok send signals.  Userspace expects signals
that come with full context information to be restartable, and many
system calls are not restartable.  read() and write() are the obvious
examples: once they're processed the beginning of the buffer, unless
they adjust their parameters, they can't safely be restarted.  So
without massive changes, I think allowing access_ok to raise a signal
with full context is asking for trouble.

I can still do the patch with two modes: signals without context via
arch_prctl and signals with context via vsyscall emulation, but that's
probably overkill for fixing this bug.  I'd say just apply these
patches as is (for 3.3).

--Andy
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