linux-hardening - [PATCH] compiler_types.h: Test for __alloc_size_

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Date:   Thu, 29 Sep 2022 01:16:42 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Kees Cook <keescook@...omium.org>, Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yonghong Song <yhs@...com>, Hao Luo <haoluo@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] compiler_types.h: Test for __alloc_size__ again

While the "alloc_size" attribute is available on all GCC versions, I
forgot that it gets disabled explicitly by the kernel in GCC < 9.1 due
to misbehaviors. Add a note to the compiler_attributes.h entry for it,
and restore the #ifdef in compiler_types.h.

Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Miguel Ojeda <ojeda@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Yonghong Song <yhs@...com>
Cc: Hao Luo <haoluo@...gle.com>
Cc: Marco Elver <elver@...gle.com>
Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Link: https://lore.kernel.org/lkml/CAMuHMdXK+UN1YVZm9DenuXAM8hZRUZJwp=SXsueP7sWiVU3a9A@mail.gmail.com
Fixes: 63caa04ec60583b1 ("slab: Remove __malloc attribute from realloc functions")
Signed-off-by: Kees Cook <keescook@...omium.org>
---
I swear I sent this earlier today, but I don't see it on lore still. Resending,
so apologies if this is a duplicate.
---
 include/linux/compiler_attributes.h | 3 ++-
 include/linux/compiler_types.h      | 9 +++++++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 465be5f072ff..55fbb6091ecf 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -65,7 +65,8 @@
 
 /*
  * Note: do not use this directly. Instead, use __alloc_size() since it is conditionally
- * available and includes other attributes.
+ * available and includes other attributes. For GCC < 9.1, __alloc_size__ gets undefined
+ * in compiler-gcc.h, due to misbehaviors.
  *
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alloc_005fsize-function-attribute
  * clang: https://clang.llvm.org/docs/AttributeReference.html#alloc-size
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index f141a6f6b9f6..0717534f8364 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -275,8 +275,13 @@ struct ftrace_likely_data {
  * be performing a _reallocation_, as that may alias the existing pointer.
  * For these, use __realloc_size().
  */
-#define __alloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__) __malloc
-#define __realloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__)
+#ifdef __alloc_size__
+# define __alloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__) __malloc
+# define __realloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__)
+#else
+# define __alloc_size(x, ...)	__malloc
+# define __realloc_size(x, ...)
+#endif
 
 #ifndef asm_volatile_goto
 #define asm_volatile_goto(x...) asm goto(x)
-- 
2.34.1