Re: [PATCH v19 00/15] arm64: untag user pointers passed to the kernel

[Will Deacon]

Hi Andrey,

On Tue, Jul 23, 2019 at 08:03:29PM +0200, Andrey Konovalov wrote:
> On Tue, Jul 23, 2019 at 7:59 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> >
> > === Overview
> >
> > arm64 has a feature called Top Byte Ignore, which allows to embed pointer
> > tags into the top byte of each pointer. Userspace programs (such as
> > HWASan, a memory debugging tool [1]) might use this feature and pass
> > tagged user pointers to the kernel through syscalls or other interfaces.
> >
> > Right now the kernel is already able to handle user faults with tagged
> > pointers, due to these patches:
> >
> > 1. 81cddd65 ("arm64: traps: fix userspace cache maintenance emulation on a
> >              tagged pointer")
> > 2. 7dcd9dd8 ("arm64: hw_breakpoint: fix watchpoint matching for tagged
> >               pointers")
> > 3. 276e9327 ("arm64: entry: improve data abort handling of tagged
> >               pointers")
> >
> > This patchset extends tagged pointer support to syscall arguments.

[...]

> Do you think this is ready to be merged?
> 
> Should this go through the mm or the arm tree?

I would certainly prefer to take at least the arm64 bits via the arm64 tree
(i.e. patches 1, 2 and 15). We also need a Documentation patch describing
the new ABI.

Will