Re: [PATCH v7 24/41] mm: Don't allow write GUPs to shadow stack memory

[Andy Lutomirski]

On Mon, Mar 6, 2023 at 5:10 AM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Mon, Feb 27, 2023 at 02:29:40PM -0800, Rick Edgecombe wrote:
> > The x86 Control-flow Enforcement Technology (CET) feature includes a new
> > type of memory called shadow stack. This shadow stack memory has some
> > unusual properties, which requires some core mm changes to function
> > properly.
> >
> > Shadow stack memory is writable only in very specific, controlled ways.
> > However, since it is writable, the kernel treats it as such. As a result
>                                                                           ^
>                                                                           ,
>
> > there remain many ways for userspace to trigger the kernel to write to
> > shadow stack's via get_user_pages(, FOLL_WRITE) operations. To make this a

Is there an alternate mechanism, or do we still want to allow
FOLL_FORCE so that debuggers can write it?

--Andy