Re: [PATCH v2 01/16] slab: Remove __malloc attribute from realloc functions

[Vlastimil Babka]

On 9/28/22 19:13, Kees Cook wrote:
> On Wed, Sep 28, 2022 at 09:26:15AM +0200, Geert Uytterhoeven wrote:
> > Hi Kees,
> >
> > On Fri, Sep 23, 2022 at 10:35 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > > The __malloc attribute should not be applied to "realloc" functions, as
> > > the returned pointer may alias the storage of the prior pointer. Instead
> > > of splitting __malloc from __alloc_size, which would be a huge amount of
> > > churn, just create __realloc_size for the few cases where it is needed.
> > >
> > > Additionally removes the conditional test for __alloc_size__, which is
> > > always defined now.
> > >
> > > Cc: Christoph Lameter <cl@xxxxxxxxx>
> > > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> > > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > Cc: Vlastimil Babka <vbabka@xxxxxxx>
> > > Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> > > Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> > > Cc: Marco Elver <elver@xxxxxxxxxx>
> > > Cc: linux-mm@xxxxxxxxx
> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> >
> > Thanks for your patch, which is now commit 63caa04ec60583b1 ("slab:
> > Remove __malloc attribute from realloc functions") in next-20220927.
> >
> > Noreply@xxxxxxxxxxxxxx reported all gcc8-based builds to fail
> > (e.g. [1], more at [2]):
> >
> >      In file included from <command-line>:
> >      ./include/linux/percpu.h: In function ‘__alloc_reserved_percpu’:
> >      ././include/linux/compiler_types.h:279:30: error: expected
> > declaration specifiers before ‘__alloc_size__’
> >       #define __alloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__) __malloc
> >                                    ^~~~~~~~~~~~~~
> >      ./include/linux/percpu.h:120:74: note: in expansion of macro ‘__alloc_size’
> >      [...]
> >
> > It's building fine with e.g. gcc-9 (which is my usual m68k cross-compiler).
> > Reverting this commit on next-20220927 fixes the issue.
> >
> > [1] http://kisskb.ellerman.id.au/kisskb/buildresult/14803908/
> > [2] http://kisskb.ellerman.id.au/kisskb/head/1bd8b75fe6adeaa89d02968bdd811ffe708cf839/
>
> Eek! Thanks for letting me know. I'm confused about this --
> __alloc_size__ wasn't optional in compiler_attributes.h -- but obviously
> I broke something! I'll go figure this out.

Even in latest next I can see at the end of include/linux/compiler-gcc.h

/*
 * Prior to 9.1, -Wno-alloc-size-larger-than (and therefore the "alloc_size"
 * attribute) do not work, and must be disabled.
 */
#if GCC_VERSION < 90100
#undef __alloc_size__
#endif



> -Kees