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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 28 Sep 2022 09:26:15 +0200
Message-ID: <CAMuHMdXK+UN1YVZm9DenuXAM8hZRUZJwp=SXsueP7sWiVU3a9A@mail.gmail.com>
Subject: Re: [PATCH v2 01/16] slab: Remove __malloc attribute from realloc functions
To:     Kees Cook <keescook@chromium.org>
Cc:     Vlastimil Babka <vbabka@suse.cz>, Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        Marco Elver <elver@google.com>, linux-mm@kvack.org,
        "Ruhl, Michael J" <michael.j.ruhl@intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Alex Elder <elder@kernel.org>,
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Hi Kees,

On Fri, Sep 23, 2022 at 10:35 PM Kees Cook <keescook@chromium.org> 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@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Roman Gushchin <roman.gushchin@linux.dev>
> Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> Cc: Marco Elver <elver@google.com>
> Cc: linux-mm@kvack.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks for your patch, which is now commit 63caa04ec60583b1 ("slab:
Remove __malloc attribute from realloc functions") in next-20220927.

Noreply@ellerman.id.au 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/


> ---
>  include/linux/compiler_types.h | 13 +++++--------
>  include/linux/slab.h           | 12 ++++++------
>  mm/slab_common.c               |  4 ++--
>  3 files changed, 13 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 4f2a819fd60a..f141a6f6b9f6 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -271,15 +271,12 @@ struct ftrace_likely_data {
>
>  /*
>   * Any place that could be marked with the "alloc_size" attribute is also
> - * a place to be marked with the "malloc" attribute. Do this as part of the
> - * __alloc_size macro to avoid redundant attributes and to avoid missing a
> - * __malloc marking.
> + * a place to be marked with the "malloc" attribute, except those that may
> + * be performing a _reallocation_, as that may alias the existing pointer.
> + * For these, use __realloc_size().
>   */
> -#ifdef __alloc_size__
> -# define __alloc_size(x, ...)  __alloc_size__(x, ## __VA_ARGS__) __malloc
> -#else
> -# define __alloc_size(x, ...)  __malloc
> -#endif
> +#define __alloc_size(x, ...)   __alloc_size__(x, ## __VA_ARGS__) __malloc
> +#define __realloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__)
>
>  #ifndef asm_volatile_goto
>  #define asm_volatile_goto(x...) asm goto(x)
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 0fefdf528e0d..41bd036e7551 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -184,7 +184,7 @@ int kmem_cache_shrink(struct kmem_cache *s);
>  /*
>   * Common kmalloc functions provided by all allocators
>   */
> -void * __must_check krealloc(const void *objp, size_t new_size, gfp_t flags) __alloc_size(2);
> +void * __must_check krealloc(const void *objp, size_t new_size, gfp_t flags) __realloc_size(2);
>  void kfree(const void *objp);
>  void kfree_sensitive(const void *objp);
>  size_t __ksize(const void *objp);
> @@ -647,10 +647,10 @@ static inline __alloc_size(1, 2) void *kmalloc_array(size_t n, size_t size, gfp_
>   * @new_size: new size of a single member of the array
>   * @flags: the type of memory to allocate (see kmalloc)
>   */
> -static inline __alloc_size(2, 3) void * __must_check krealloc_array(void *p,
> -                                                                   size_t new_n,
> -                                                                   size_t new_size,
> -                                                                   gfp_t flags)
> +static inline __realloc_size(2, 3) void * __must_check krealloc_array(void *p,
> +                                                                     size_t new_n,
> +                                                                     size_t new_size,
> +                                                                     gfp_t flags)
>  {
>         size_t bytes;
>
> @@ -774,7 +774,7 @@ static inline __alloc_size(1, 2) void *kvcalloc(size_t n, size_t size, gfp_t fla
>  }
>
>  extern void *kvrealloc(const void *p, size_t oldsize, size_t newsize, gfp_t flags)
> -                     __alloc_size(3);
> +                     __realloc_size(3);
>  extern void kvfree(const void *addr);
>  extern void kvfree_sensitive(const void *addr, size_t len);
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 17996649cfe3..457671ace7eb 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1134,8 +1134,8 @@ module_init(slab_proc_init);
>
>  #endif /* CONFIG_SLAB || CONFIG_SLUB_DEBUG */
>
> -static __always_inline void *__do_krealloc(const void *p, size_t new_size,
> -                                          gfp_t flags)
> +static __always_inline __realloc_size(2) void *
> +__do_krealloc(const void *p, size_t new_size, gfp_t flags)
>  {
>         void *ret;
>         size_t ks;
> --
> 2.34.1
>


--
Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds