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

On 9/28/22 09:26, Geert Uytterhoeven wrote:

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.

So IIUC it was wrong to remove the #ifdefs?

[1] http://kisskb.ellerman.id.au/kisskb/buildresult/14803908/ [2] http://kisskb.ellerman.id.au/kisskb/head/1bd8b75fe6adeaa89d02968bdd811ffe708...

...

---

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