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SubjectRe: [PATCH v8 0/8] arm64: untag user pointers passed to the kernel
Hi Andrey,

On Thu, Nov 08, 2018 at 03:48:10PM +0100, Andrey Konovalov wrote:
> On Thu, Nov 8, 2018 at 3:36 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> > Changes in v8:
> > - Rebased onto 65102238 (4.20-rc1).
> > - Added a note to the cover letter on why syscall wrappers/shims that untag
> > user pointers won't work.
> > - Added a note to the cover letter that this patchset has been merged into
> > the Pixel 2 kernel tree.
> > - Documentation fixes, in particular added a list of syscalls that don't
> > support tagged user pointers.
>
> I've changed the documentation to be more specific, please take a look.
>
> I haven't done anything about adding a way for the user to find out
> that the kernel supports this ABI extension. I don't know what would
> the the preferred way to do this, and we haven't received any comments
> on that from anybody else. Probing "on some innocuous syscall
> currently returning -EFAULT on tagged pointer arguments" works though,
> as you mentioned.

We've had some internal discussions and also talked to some people at
Plumbers. I think the best option is to introduce an AT_FLAGS bit to
describe the ABI relaxation on tagged pointers. Vincenzo is going to
propose a patch on top of this series.

> As mentioned in the cover letter, this patchset has been merged into
> the Pixel 2 kernel tree.

I just hope it's not enabled on production kernels, it would introduce
a user ABI that may differ from what ends up upstream.

--
Catalin

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