From 5e88c48cb4bcbd0ea683373a106268933bb4edd2 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 18 Apr 2025 14:32:39 -0700 Subject: kbuild: Switch from -Wvla to -Wvla-larger-than=1 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=N option (though GCC may split -Wvla similarly[3] to how Clang is planning to). While GCC 8+ supports -Wvla-larger-than, only 9+ supports ...=0[4], so use -Wvla-larger-than=1. Adjust mm/kasan/Makefile to remove it from CFLAGS (GCC <9 appears unable to disable the warning correctly[5]). The VLA usage in lib/test_ubsan.c was removed in commit 9d7ca61b1366 ("lib/test_ubsan.c: VLA no longer used in kernel") so the lib/Makefile disabling of VLA checking can be entirely removed. 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] Link: https://lore.kernel.org/lkml/7780883c-0ac8-4aaa-b850-469e33b50672@linux.ibm.com/ [4] Link: https://lore.kernel.org/r/202505071331.4iOzqmuE-lkp@intel.com/ [5] Reviewed-by: Nathan Chancellor Reviewed-by: Christoph Hellwig Tested-by: Venkat Rao Bagalkote Link: https://lore.kernel.org/r/20250418213235.work.532-kees@kernel.org Signed-off-by: Kees Cook --- lib/Makefile | 1 - 1 file changed, 1 deletion(-) (limited to 'lib/Makefile') diff --git a/lib/Makefile b/lib/Makefile index f07b24ce1b3f..c38582f187dd 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -71,7 +71,6 @@ 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 += $(call cc-disable-warning, unused-but-set-variable) UBSAN_SANITIZE_test_ubsan.o := y obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o -- cgit v1.2.3