@@ -71,7 +71,7 @@ CFLAGS_test_bitops.o += -Werror
obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
obj-$(CONFIG_TEST_IDA) += test_ida.o
obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o
-CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
+CFLAGS_test_ubsan.o += $(call cc-option, -Wno-vla-larger-than)
CFLAGS_test_ubsan.o += $(call cc-disable-warning, unused-but-set-variable)
UBSAN_SANITIZE_test_ubsan.o := y
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
@@ -35,7 +35,7 @@ CFLAGS_shadow.o := $(CC_FLAGS_KASAN_RUNTIME)
CFLAGS_hw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
CFLAGS_sw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
-CFLAGS_KASAN_TEST := $(CFLAGS_KASAN) $(call cc-disable-warning, vla)
+CFLAGS_KASAN_TEST := $(CFLAGS_KASAN) $(call cc-option, -Wno-vla-larger-than)
ifndef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
# If compiler instruments memintrinsics by prefixing them with __asan/__hwasan,
# we need to treat them normally (as builtins), otherwise the compiler won't
@@ -45,8 +45,13 @@ endif
# These result in bogus false positives
KBUILD_CFLAGS += $(call cc-disable-warning, dangling-pointer)
-# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
-KBUILD_CFLAGS += -Wvla
+# Stack Variable Length Arrays (VLAs) must not be used in the kernel.
+# Function array parameters should, however, be usable, but -Wvla will
+# warn for those. Clang has no way yet to distinguish between the VLA
+# types, so depend on GCC for now to keep stack VLAs out of the tree.
+# https://github.com/llvm/llvm-project/issues/57098
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98217
+KBUILD_CFLAGS += $(call cc-option,-Wvla-larger-than=0)
# disable pointer signed / unsigned warnings in gcc 4.0
KBUILD_CFLAGS += -Wno-pointer-sign
Variable Length Arrays (VLAs) on the stack must not be used in the kernel. Function parameter VLAs[1] should be usable, but -Wvla will warn for those. For example, this will produce a warning but it is not using a stack VLA: int something(size_t n, int array[n]) { ... Clang has no way yet to distinguish between the VLA types[2], so depend on GCC for now to keep stack VLAs out of the tree by using GCC's -Wvla-larger-than=0 option (though GCC may split -Wvla[3] similarly to how Clang is planning to). Switch to -Wvla-larger-than=0 and adjust the two VLA-checking selftests to disable the updated option name. Link: https://en.cppreference.com/w/c/language/array [1] Link: https://github.com/llvm/llvm-project/issues/57098 [2] Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98217 [3] Signed-off-by: Kees Cook <kees@kernel.org> --- Cc: Christoph Hellwig <hch@lst.de> Cc: Masahiro Yamada <masahiroy@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Konovalov <andreyknvl@gmail.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Nicolas Schier <nicolas.schier@linux.dev> Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com> Cc: Bill Wendling <morbo@google.com> Cc: Justin Stitt <justinstitt@google.com> Cc: <kasan-dev@googlegroups.com> Cc: <linux-mm@kvack.org> Cc: <linux-kbuild@vger.kernel.org> Cc: <llvm@lists.linux.dev> --- lib/Makefile | 2 +- mm/kasan/Makefile | 2 +- scripts/Makefile.extrawarn | 9 +++++++-- 3 files changed, 9 insertions(+), 4 deletions(-)