Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free()

[Song Liu]

On Fri, Apr 19, 2024 at 10:03 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
[...]
> > >
> > > [1] https://lore.kernel.org/all/20240411160526.2093408-1-rppt@xxxxxxxxxx
> >
> > For the ROX to work, we need different users (module text, kprobe, etc.) to have
> > the same execmem_range. From [1]:
> >
> > static void *execmem_cache_alloc(struct execmem_range *range, size_t size)
> > {
> > ...
> >        p = __execmem_cache_alloc(size);
> >        if (p)
> >                return p;
> >       err = execmem_cache_populate(range, size);
> > ...
> > }
> >
> > We are calling __execmem_cache_alloc() without range. For this to work,
> > we can only call execmem_cache_alloc() with one execmem_range.
>
> Actually, on x86 this will "just work" because everything shares the same
> address space :)
>
> The 2M pages in the cache will be in the modules space, so
> __execmem_cache_alloc() will always return memory from that address space.
>
> For other architectures this indeed needs to be fixed with passing the
> range to __execmem_cache_alloc() and limiting search in the cache for that
> range.

I think we at least need the "map to" concept (initially proposed by Thomas)
to get this work. For example, EXECMEM_BPF and EXECMEM_KPROBE
maps to EXECMEM_MODULE_TEXT, so that all these actually share
the same range.

Does this make sense?

Song