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

Mike Rapoport
2024-04-19T20:00:57Z

On Fri, Apr 19, 2024 at 10:32:39AM -0700, Song Liu wrote:
> On Fri, Apr 19, 2024 at 10:03 AM Mike Rapoport <rppt@kernel.org> wrote:
> [...]
> > > >
> > > > [1] https://lore.kernel.org/all/20240411160526.2093408-1-rppt@kernel.org
> > >
> > > 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.

Why?

> Does this make sense?
>
> Song

--
Sincerely yours,
Mike.