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![Kees Cook](/assets/img/avatar_default.png)
In order to do kernel builds with the bounds checker individually available, introduce CONFIG_UBSAN_BOUNDS, with the remaining options under CONFIG_UBSAN_MISC. For example, using this, we can start to expand the coverage syzkaller is providing. Right now, all of UBSan is disabled for syzbot builds because taken as a whole, it is too noisy. This will let us focus on one feature at a time. For the bounds checker specifically, this provides a mechanism to eliminate an entire class of array overflows with close to zero performance overhead (I cannot measure a difference). In my (mostly) defconfig, enabling bounds checking adds ~4200 checks to the kernel. Performance changes are in the noise, likely due to the branch predictors optimizing for the non-fail path. Some notes on the bounds checker: - it does not instrument {mem,str}*()-family functions, it only instruments direct indexed accesses (e.g. "foo[i]"). Dealing with the {mem,str}*()-family functions is a work-in-progress around CONFIG_FORTIFY_SOURCE[1]. - it ignores flexible array members, including the very old single byte (e.g. "int foo[1];") declarations. (Note that GCC's implementation appears to ignore _all_ trailing arrays, but Clang only ignores empty, 0, and 1 byte arrays[2].) [1] https://github.com/KSPP/linux/issues/6 [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92589 Suggested-by: Elena Petrova <lenaptr@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Acked-by: Dmitry Vyukov <dvyukov@google.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Konovalov <andreyknvl@google.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Dan Carpenter <dan.carpenter@oracle.com> Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com> Link: http://lkml.kernel.org/r/20200227193516.32566-3-keescook@chromium.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
29 lines
1 KiB
Makefile
29 lines
1 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
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ifdef CONFIG_UBSAN
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ifdef CONFIG_UBSAN_ALIGNMENT
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment)
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endif
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ifdef CONFIG_UBSAN_BOUNDS
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
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endif
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ifdef CONFIG_UBSAN_MISC
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=shift)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=integer-divide-by-zero)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=unreachable)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=signed-integer-overflow)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=object-size)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=bool)
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CFLAGS_UBSAN += $(call cc-option, -fsanitize=enum)
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endif
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ifdef CONFIG_UBSAN_TRAP
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CFLAGS_UBSAN += $(call cc-option, -fsanitize-undefined-trap-on-error)
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endif
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# -fsanitize=* options makes GCC less smart than usual and
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# increase number of 'maybe-uninitialized false-positives
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CFLAGS_UBSAN += $(call cc-option, -Wno-maybe-uninitialized)
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endif
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