Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64

[Marco Elver]

On Mon, 21 Sep 2020 at 16:31, Will Deacon <will@xxxxxxxxxx> wrote:
> On Mon, Sep 21, 2020 at 03:26:04PM +0200, Marco Elver wrote:
> > Add architecture specific implementation details for KFENCE and enable
> > KFENCE for the arm64 architecture. In particular, this implements the
> > required interface in <asm/kfence.h>. Currently, the arm64 version does
> > not yet use a statically allocated memory pool, at the cost of a pointer
> > load for each is_kfence_address().
[...]
> > For ARM64, we would like to solicit feedback on what the best option is
> > to obtain a constant address for __kfence_pool. One option is to declare
> > a memory range in the memory layout to be dedicated to KFENCE (like is
> > done for KASAN), however, it is unclear if this is the best available
> > option. We would like to avoid touching the memory layout.

> Given that the pool is relatively small (i.e. when compared with our virtual
> address space), dedicating an area of virtual space sounds like it makes
> the most sense here. How early do you need it to be available?

Note: we're going to send a v4 this or next week with a few other
minor fixes in it. But I think we just don't want to block the entire
series on figuring out what the static-pool arm64 version should do,
especially if we'll have a few iterations with only this patch here
changing.

So the plan will be:

1. Send v4, which could from our point-of-view be picked up for
merging. Unless of course there are more comments.

2. Work out the details for the static-pool arm64 version, since it
doesn't seem trivial to do the same thing as we do for x86. In
preparation for that, v4 will allow the __kfence_pool's attributes to
be defined entirely by <asm/kfence.h>, so that we can fiddle with
sections etc.

3. Send patch switching out the simpler arm64 version here for one
that places __kfence_pool at a static location.

Hopefully that plan is reasonable.

Thanks,
-- Marco