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authorKees Cook <keescook@chromium.org>2020-04-06 20:12:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-07 10:43:44 -0700
commit277a10850f9f4cb3429faf59293e2c89b1a320be (patch)
tree7dc396263940e86c5055f50e4095b427dfd46cdf
parent0887a7ebc97770c7870abf3075a2e8cd502a7f52 (diff)
downloadlinux-277a10850f9f4cb3429faf59293e2c89b1a320be.tar.bz2
ubsan: split "bounds" checker from other options
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>
-rw-r--r--lib/Kconfig.ubsan29
-rw-r--r--scripts/Makefile.ubsan7
2 files changed, 30 insertions, 6 deletions
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
index 9deb655838b0..48469c95d78e 100644
--- a/lib/Kconfig.ubsan
+++ b/lib/Kconfig.ubsan
@@ -2,7 +2,7 @@
config ARCH_HAS_UBSAN_SANITIZE_ALL
bool
-config UBSAN
+menuconfig UBSAN
bool "Undefined behaviour sanity checker"
help
This option enables the Undefined Behaviour sanity checker.
@@ -10,9 +10,10 @@ config UBSAN
behaviours at runtime. For more details, see:
Documentation/dev-tools/ubsan.rst
+if UBSAN
+
config UBSAN_TRAP
bool "On Sanitizer warnings, abort the running kernel code"
- depends on UBSAN
depends on $(cc-option, -fsanitize-undefined-trap-on-error)
help
Building kernels with Sanitizer features enabled tends to grow
@@ -25,9 +26,26 @@ config UBSAN_TRAP
the system. For some system builders this is an acceptable
trade-off.
+config UBSAN_BOUNDS
+ bool "Perform array index bounds checking"
+ default UBSAN
+ help
+ This option enables detection of directly indexed out of bounds
+ array accesses, where the array size is known at compile time.
+ Note that this does not protect array overflows via bad calls
+ to the {str,mem}*cpy() family of functions (that is addressed
+ by CONFIG_FORTIFY_SOURCE).
+
+config UBSAN_MISC
+ bool "Enable all other Undefined Behavior sanity checks"
+ default UBSAN
+ help
+ This option enables all sanity checks that don't have their
+ own Kconfig options. Disable this if you only want to have
+ individually selected checks.
+
config UBSAN_SANITIZE_ALL
bool "Enable instrumentation for the entire kernel"
- depends on UBSAN
depends on ARCH_HAS_UBSAN_SANITIZE_ALL
# We build with -Wno-maybe-uninitilzed, but we still want to
@@ -44,7 +62,6 @@ config UBSAN_SANITIZE_ALL
config UBSAN_NO_ALIGNMENT
bool "Disable checking of pointers alignment"
- depends on UBSAN
default y if HAVE_EFFICIENT_UNALIGNED_ACCESS
help
This option disables the check of unaligned memory accesses.
@@ -57,7 +74,9 @@ config UBSAN_ALIGNMENT
config TEST_UBSAN
tristate "Module for testing for undefined behavior detection"
- depends on m && UBSAN
+ depends on m
help
This is a test module for UBSAN.
It triggers various undefined behavior, and detect it.
+
+endif # if UBSAN
diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
index 668a91510bfe..5b15bc425ec9 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -5,14 +5,19 @@ ifdef CONFIG_UBSAN_ALIGNMENT
CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment)
endif
+ifdef CONFIG_UBSAN_BOUNDS
+ CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
+endif
+
+ifdef CONFIG_UBSAN_MISC
CFLAGS_UBSAN += $(call cc-option, -fsanitize=shift)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=integer-divide-by-zero)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=unreachable)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=signed-integer-overflow)
- CFLAGS_UBSAN += $(call cc-option, -fsanitize=bounds)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=object-size)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=bool)
CFLAGS_UBSAN += $(call cc-option, -fsanitize=enum)
+endif
ifdef CONFIG_UBSAN_TRAP
CFLAGS_UBSAN += $(call cc-option, -fsanitize-undefined-trap-on-error)