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

Vlastimil Babka <vbabka@xxxxxxx> · Wed, 28 Sep 2022 18:27:36 +0200

On 9/28/22 09:26, 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.

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/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@xxxxxxxxxxxxxx

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








