Re: [RFC][PATCH 0/4] slab: Allow for type introspection during allocation

Kees Cook
2024-07-09T23:28:32Z

On Tue, Jul 09, 2024 at 11:02:55PM +0200, Marco Elver wrote:
> On Tue, 9 Jul 2024 at 22:28, Kees Cook <kees@kernel.org> wrote:
> >
> > On Tue, Jul 09, 2024 at 10:26:32AM -0700, Christoph Lameter (Ampere) wrote:
> > > On Mon, 8 Jul 2024, Kees Cook wrote:
> > >
> > > >
> > > > obj = kmalloc(obj, gfp);
> > >
> > > Could we avoid repeating "obj" in this pattern?
> > >
> > > F.e.
> > >
> > > KMALLOC(obj, gfp);
> >
> > This appears to be the common feedback, which is good! :) And we can
> > still have it return "obj" as well, so it could still be used in
> > "return" statements, etc. I will work up a new RFC...
>
> More macros like this only obfuscate the code further. The name would
> become something that makes it really clear there's an assignment.
>
> assign_kmalloc(obj, gfp)
>
> There may be better options. Also ALLCAPS could be avoided here, as we
> have done with other language-like features (vs. pure constants).

So, in looking a code patterns, it seems what we really want more than
returning the object that was allocated is actually returning the size
of the allocation size requested. i.e.:

info->size = struct_size(ptr, flex_member, count);
info->obj = kmalloc(info->size, gfp);

would become:

info->size = kmalloc(info->obj, flex_member, count, gfp);

-Kees

--
Kees Cook