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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>
83 lines
2.9 KiB
Plaintext
83 lines
2.9 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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config ARCH_HAS_UBSAN_SANITIZE_ALL
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bool
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menuconfig UBSAN
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bool "Undefined behaviour sanity checker"
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help
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This option enables the Undefined Behaviour sanity checker.
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Compile-time instrumentation is used to detect various undefined
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behaviours at runtime. For more details, see:
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Documentation/dev-tools/ubsan.rst
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if UBSAN
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config UBSAN_TRAP
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bool "On Sanitizer warnings, abort the running kernel code"
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depends on $(cc-option, -fsanitize-undefined-trap-on-error)
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help
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Building kernels with Sanitizer features enabled tends to grow
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the kernel size by around 5%, due to adding all the debugging
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text on failure paths. To avoid this, Sanitizer instrumentation
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can just issue a trap. This reduces the kernel size overhead but
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turns all warnings (including potentially harmless conditions)
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into full exceptions that abort the running kernel code
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(regardless of context, locks held, etc), which may destabilize
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the system. For some system builders this is an acceptable
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trade-off.
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config UBSAN_BOUNDS
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bool "Perform array index bounds checking"
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default UBSAN
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help
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This option enables detection of directly indexed out of bounds
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array accesses, where the array size is known at compile time.
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Note that this does not protect array overflows via bad calls
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to the {str,mem}*cpy() family of functions (that is addressed
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by CONFIG_FORTIFY_SOURCE).
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config UBSAN_MISC
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bool "Enable all other Undefined Behavior sanity checks"
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default UBSAN
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help
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This option enables all sanity checks that don't have their
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own Kconfig options. Disable this if you only want to have
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individually selected checks.
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config UBSAN_SANITIZE_ALL
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bool "Enable instrumentation for the entire kernel"
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depends on ARCH_HAS_UBSAN_SANITIZE_ALL
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# We build with -Wno-maybe-uninitilzed, but we still want to
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# use -Wmaybe-uninitilized in allmodconfig builds.
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# So dependsy bellow used to disable this option in allmodconfig
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depends on !COMPILE_TEST
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default y
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help
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This option activates instrumentation for the entire kernel.
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If you don't enable this option, you have to explicitly specify
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UBSAN_SANITIZE := y for the files/directories you want to check for UB.
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Enabling this option will get kernel image size increased
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significantly.
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config UBSAN_NO_ALIGNMENT
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bool "Disable checking of pointers alignment"
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default y if HAVE_EFFICIENT_UNALIGNED_ACCESS
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help
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This option disables the check of unaligned memory accesses.
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This option should be used when building allmodconfig.
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Disabling this option on architectures that support unaligned
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accesses may produce a lot of false positives.
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config UBSAN_ALIGNMENT
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def_bool !UBSAN_NO_ALIGNMENT
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config TEST_UBSAN
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tristate "Module for testing for undefined behavior detection"
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depends on m
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help
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This is a test module for UBSAN.
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It triggers various undefined behavior, and detect it.
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endif # if UBSAN
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