[PATCH] x86: Remove ARCH_CET_LEGACY_BITMAP [BZ #25397]

[H.J. Lu]

On Sat, Mar 7, 2020 at 4:08 AM Florian Weimer <fw@deneb.enyo.de> wrote:
>
> * H. J. Lu:
>
> > +  funcp = mmap (NULL, 0x1000, PROT_EXEC | PROT_READ | PROT_WRITE,
> > +             MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>
> An alternative approach would automatically allocate a legacy bitmap
> for RWX mappings under the right circumstances (maybe even looking and

Also mprotect.

> the caller address in mmap).  Have you considered that?

It can become very complicated since mmap and mprotect can be called
indirectly.   It is hard to tell if the real user of such memory is legacy code
or not.

> I'm not question the removal of the legacy bitmap as such.  It looks
> like the right call.  I just want to collect some thoughts for
> posterity.

I think we should leave out legacy bitmap in the first phase.   We can
always put it back later.

BTW, now I can boot the updated Fedora 31 in GUI on CET processor with
CET enabled kernel.

-- 
H.J.