Re: [PATCH 2/2] riscv: mm: Update mmap_rnd_bits_max

Sami Tolvanen
2023-09-29T22:53:02Z

On Fri, Sep 29, 2023 at 2:54 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Sep 29, 2023 at 09:11:58PM +0000, Sami Tolvanen wrote:
> > ARCH_MMAP_RND_BITS_MAX is based on Sv39, which leaves a few
> > potential bits of mmap randomness on the table if we end up enabling
> > 4/5-level paging. Update mmap_rnd_bits_max to take the final address
> > space size into account. This increases mmap_rnd_bits_max from 24 to
> > 33 with Sv48/57.
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
>
> I like this. Is RISCV the only arch where the paging level can be chosen
> at boot time?

I haven't seen this elsewhere, but I also haven't looked at all the
other architectures that closely. arm64 does something interesting
with ARM64_VA_BITS_52, but I think we can still handle that in
Kconfig.

Sami