[PATCH] Compiler Attributes: Check GCC version for __alloc_size attribute

From: Kees Cook
Date: Fri Sep 10 2021 - 12:58:58 EST

Unfortunately, just version checking the use of -Wno-alloc-size-larger-than
is not sufficient to make the __alloc_size attribute behave correctly
under older GCC versions. The attribute itself must be disabled in those
situations too, as there appears to be no way to reliably silence the
SIZE_MAX constant expression cases for GCC versions less than 9.1:

In file included from ./include/linux/resource_ext.h:11,
from ./include/linux/pci.h:40,
from drivers/net/ethernet/intel/ixgbe/ixgbe.h:9,
from drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c:4:
In function 'kmalloc_node',
inlined from 'ixgbe_alloc_q_vector' at ./include/linux/slab.h:743:9:
./include/linux/slab.h:618:9: error: argument 1 value '18446744073709551615' exceeds maximum object size 9223372036854775807 [-Werror=alloc-size-larger-than=]
return __kmalloc_node(size, flags, node);
./include/linux/slab.h: In function 'ixgbe_alloc_q_vector':
./include/linux/slab.h:455:7: note: in a call to allocation function '__kmalloc_node' declared here
void *__kmalloc_node(size_t size, gfp_t flags, int node) __assume_slab_alignment __malloc;

-Wno-alloc-size-larger-than is not correctly handled by GCC < 9.1
https://godbolt.org/z/hqsfG7q84 (doesn't disable)
https://godbolt.org/z/P9jdrPTYh (doesn't admit to not knowing about option)
https://godbolt.org/z/465TPMWKb (only warns when other warnings appear)

-Walloc-size-larger-than=18446744073709551615 is not handled by GCC < 8
https://godbolt.org/z/73hh1EPxz (ignores numeric value)

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Miguel Ojeda <ojeda@xxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Arvind Sankar <nivedita@xxxxxxxxxxxx>
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: llvm@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
I've been digging through older GCC build logs and found this needed to
be fixed even harder than prior attempts from what Randy had been seeing.
include/linux/compiler-gcc.h | 9 +++++++++
include/linux/compiler_attributes.h | 6 ------
include/linux/compiler_types.h | 5 +++++
3 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 01985821944b..ffe0a7570d66 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -151,3 +151,12 @@
#define __diag_GCC_8(s)
+ * https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alloc_005fsize-function-attribute
+ * However, prior to 9.1, -Wno-alloc-size-larger-than does not work,
+ * making this attribute unusable.
+ */
+#if GCC_VERSION < 90100
+#define __alloc_size /**/
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 19f178e20e61..2487be0e7199 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -53,12 +53,6 @@
#define __aligned(x) __attribute__((__aligned__(x)))
#define __aligned_largest __attribute__((__aligned__))

- * 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
- */
-#define __alloc_size(x, ...) __attribute__((__alloc_size__(x, ## __VA_ARGS__)))
* Note: users of __always_inline currently do not write "inline" themselves,
* which seems to be required by gcc to apply the attribute according
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index c43308b0a9a9..91de9bead40d 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -254,6 +254,11 @@ struct ftrace_likely_data {
#define asm_volatile_goto(x...) asm goto(x)

+/* If not specifically disabled, allow the use of __alloc_size attribute. */
+#ifndef __alloc_size
+# define __alloc_size(x, ...) __attribute__((__alloc_size__(x, ## __VA_ARGS__)))
#define asm_inline asm __inline