| Message ID | 20191120010636.27368-3-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ubsan: Split out bounds checker | expand |
On 11/20/19 4:06 AM, Kees Cook wrote: > 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> Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index d69e8b21ebae..f5ed2dceef30 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -22,6 +22,25 @@ config UBSAN_TRAP can just issue a trap. This reduces the kernel size overhead but turns all warnings into full thread-killing exceptions. +config UBSAN_BOUNDS + bool "Perform array bounds checking" + depends on UBSAN + default UBSAN + help + This option enables detection of direct out of bounds array + accesses, where the array size is known at compile time. Note + that this does not protect character array overflows due to + bad calls to the {str,mem}*cpy() family of functions. + +config UBSAN_MISC + bool "Enable all other Undefined Behavior sanity checks" + depends on UBSAN + 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 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)
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> --- lib/Kconfig.ubsan | 19 +++++++++++++++++++ scripts/Makefile.ubsan | 7 ++++++- 2 files changed, 25 insertions(+), 1 deletion(-)