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authorKees Cook <keescook@chromium.org>2023-05-17 16:18:11 -0700
committerKees Cook <keescook@chromium.org>2023-05-22 12:33:53 -0700
commitdf8fc4e934c12b906d08050d7779f292b9c5c6b5 (patch)
treeeff293b0a9ca59c1f4a7e017d8447be5efb639a6 /Makefile
parent08e4044243a668ea2801cebffcb7c07df568ed3f (diff)
kbuild: Enable -fstrict-flex-arrays=3
The -fstrict-flex-arrays=3 option is now available with the release of GCC 13[1] and Clang 16[2]. This feature instructs the compiler to treat only C99 flexible arrays as dynamically sized for the purposes of object size calculations. In other words, the ancient practice of using 1-element arrays, or the GNU extension of using 0-sized arrays, as a dynamically sized array is disabled. This allows CONFIG_UBSAN_BOUNDS, CONFIG_FORTIFY_SOURCE, and other object-size aware features to behave unambiguously in the face of trailing arrays: only C99 flexible arrays are considered to be dynamically sized. For yet more detail, see: https://people.kernel.org/kees/bounded-flexible-arrays-in-c Enabling this will help track down any outstanding cases of fake flexible arrays that need attention in kernel code. [1] https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html#index-fstrict-flex-arrays [2] https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fstrict-flex-arrays Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Nicolas Schier <nicolas@fjasle.eu> Cc: linux-kbuild@vger.kernel.org Co-developed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org> Signed-off-by: "Gustavo A. R. Silva" <gustavoars@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile6
1 files changed, 6 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index f836936fb4d8..07e5aec1daf5 100644
--- a/Makefile
+++ b/Makefile
@@ -1026,6 +1026,12 @@ KBUILD_CFLAGS += -Wno-pointer-sign
# globally built with -Wcast-function-type.
KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)
+# To gain proper coverage for CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE,
+# the kernel uses only C99 flexible arrays for dynamically sized trailing
+# arrays. Enforce this for everything that may examine structure sizes and
+# perform bounds checking.
+KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3)
+
# disable stringop warnings in gcc 8+
KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)