kbuild: Switch from -Wvla to -Wvla-larger-than=0
Subsystems (5)
PATCH 1/1 kbuild: Switch from -Wvla to -Wvla-larger-than=0
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.
---
Cc: Christoph Hellwig <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Vincenzo Frascino <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nicolas Schier <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Bill Wendling <[email protected]>
Cc: Justin Stitt <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
--- lib/Makefile | 2 +- mm/kasan/Makefile | 2 +- scripts/Makefile.extrawarn | 9 +++++++-- 3 files changed, 9 insertions(+), 4 deletions(-)
lib/Makefile +1 -1
@@ -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
mm/kasan/Makefile +1 -1
@@ -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
scripts/Makefile.extrawarn +7 -2
@@ -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 += $(call cc-option,-Wvla-larger-than=0) # disable pointer signed / unsigned warnings in gcc 4.0 KBUILD_CFLAGS += -Wno-pointer-sign
Signature · 1 line
2.34.1
Looks good:
Note that sparse currently also can't cope with VLAs including the prototype syntax, which also needs addressing.
Quoted 12 lines · Kees Cook
Variable Length Arrays (VLAs) on the stack must not be used in the kernel. Function parameter VLAs[1] should be usable, but -Wvla will warn for those. For example, this will produce a warning but it is not using a stack VLA:
int
something(size_t n, int array[n]){ ...Clang has no way yet to distinguish between the VLA types[2], so depend on GCC for now to keep stack VLAs out of the tree by using GCC's -Wvla-larger-than=0 option (though GCC may split -Wvla[3] similarly to how Clang is planning to).
Quoted 7 lines
Switch to -Wvla-larger-than=0 and adjust the two VLA-checking selftests to disable the updated option name.
Quoted 54 lines
lib/Makefile | 2 +- mm/kasan/Makefile | 2 +- scripts/Makefile.extrawarn | 9 +++++++-- 3 files changed, 9 insertions(+), 4 deletions(-)lib/Makefile +1
-1@@ -71,7 +71,7 @@ CFLAGS_test_bitops.o += -Werror obj-$(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.omm/kasan/Makefile +1
-1@@ -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'tscripts/Makefile.extrawarn +7
-2@@ -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-signSignature · 1 line
2.34.1
Quoted 6 lines · Christoph Hellwig
Looks good:
Reviewed-by Christoph Hellwig <[email protected]>Note that sparse currently also can't cope with VLAs including the prototype syntax, which also needs addressing.
Hm, it looks like it's been over a year since a commit to the sparse git.
Luc, are function prototypes with VLAs likely to be supported by sparse soon?
Signature · 1 line
Kees Cook
Kees Cook
AppliedQuoted 8 lines · Kees Cook
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]){ ...[...]
Applied to for-next/hardening, thanks!
[1/1] kbuild: Switch from -Wvla to -Wvla-larger-than=0
https://git.kernel.org/kees/c/9c2cfa10444c
Take care,
Signature · 1 line
Kees Cook