In order to mitigate unexpected signed wrap-around[1], bring back the signed integer overflow sanitizer. It was removed in commit 6aaa31aeb9cf ("ubsan: remove overflow checks") because it was effectively a no-op when combined with -fno-strict-overflow (which correctly changes signed overflow from being "undefined" to being explicitly "wrap around").
Compilers are adjusting their sanitizers to trap wrap-around and to detecting common code patterns that should not be instrumented (e.g. "var + offset < var"). Prepare for this and explicitly rename the option from "OVERFLOW" to "WRAP". To annotate intentional wrap-around arithmetic, the add/sub/mul_wrap() helpers can be used for individual statements. At the function level, the __signed_wrap attribute can be used to mark an entire function as expecting its signed arithmetic to wrap around. For a single object file the Makefile can use "UBSAN_WRAP_SIGNED_target.o := n" to mark it as wrapping, and for an entire directory, "UBSAN_WRAP_SIGNED := n" can be used. Additionally keep these disabled under CONFIG_COMPILE_TEST for now. Link: https://github.com/KSPP/linux/issues/26 [1] Cc: Justin Stitt <justinst...@google.com> Cc: Marco Elver <el...@google.com> Cc: Miguel Ojeda <oj...@kernel.org> Cc: Nathan Chancellor <nat...@kernel.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Hao Luo <hao...@google.com> Signed-off-by: Kees Cook <keesc...@chromium.org> --- v3: - split out signed overflow sanitizer so we can do each separately v2: https://lore.kernel.org/all/20240202101311.it.893-k...@kernel.org/ v1: https://lore.kernel.org/all/20240129175033.work.813-k...@kernel.org/ --- include/linux/compiler_types.h | 9 ++++- lib/Kconfig.ubsan | 14 +++++++ lib/test_ubsan.c | 37 ++++++++++++++++++ lib/ubsan.c | 68 ++++++++++++++++++++++++++++++++++ lib/ubsan.h | 4 ++ scripts/Makefile.lib | 3 ++ scripts/Makefile.ubsan | 3 ++ 7 files changed, 137 insertions(+), 1 deletion(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 6f1ca49306d2..ee9d272008a5 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -282,11 +282,18 @@ struct ftrace_likely_data { #define __no_sanitize_or_inline __always_inline #endif +/* Do not trap wrapping arithmetic within an annotated function. */ +#ifdef CONFIG_UBSAN_SIGNED_WRAP +# define __signed_wrap __attribute__((no_sanitize("signed-integer-overflow"))) +#else +# define __signed_wrap +#endif + /* Section for code which can't be instrumented at all */ #define __noinstr_section(section) \ noinline notrace __attribute((__section__(section))) \ __no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage \ - __no_sanitize_memory + __no_sanitize_memory __signed_wrap #define noinstr __noinstr_section(".noinstr.text") diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan index 56d7653f4941..129e9bc21877 100644 --- a/lib/Kconfig.ubsan +++ b/lib/Kconfig.ubsan @@ -116,6 +116,20 @@ config UBSAN_UNREACHABLE This option enables -fsanitize=unreachable which checks for control flow reaching an expected-to-be-unreachable position. +config UBSAN_SIGNED_WRAP + bool "Perform checking for signed arithmetic wrap-around" + default UBSAN + depends on !COMPILE_TEST + depends on $(cc-option,-fsanitize=signed-integer-overflow) + help + This option enables -fsanitize=signed-integer-overflow which checks + for wrap-around of any arithmetic operations with signed integers. + This currently performs nearly no instrumentation due to the + kernel's use of -fno-strict-overflow which converts all would-be + arithmetic undefined behavior into wrap-around arithmetic. Future + sanitizer versions will allow for wrap-around checking (rather than + exclusively undefined behavior). + config UBSAN_BOOL bool "Perform checking for non-boolean values used as boolean" default UBSAN diff --git a/lib/test_ubsan.c b/lib/test_ubsan.c index f4ee2484d4b5..276c12140ee2 100644 --- a/lib/test_ubsan.c +++ b/lib/test_ubsan.c @@ -11,6 +11,39 @@ typedef void(*test_ubsan_fp)(void); #config, IS_ENABLED(config) ? "y" : "n"); \ } while (0) +static void test_ubsan_add_overflow(void) +{ + volatile int val = INT_MAX; + + UBSAN_TEST(CONFIG_UBSAN_SIGNED_WRAP); + val += 2; +} + +static void test_ubsan_sub_overflow(void) +{ + volatile int val = INT_MIN; + volatile int val2 = 2; + + UBSAN_TEST(CONFIG_UBSAN_SIGNED_WRAP); + val -= val2; +} + +static void test_ubsan_mul_overflow(void) +{ + volatile int val = INT_MAX / 2; + + UBSAN_TEST(CONFIG_UBSAN_SIGNED_WRAP); + val *= 3; +} + +static void test_ubsan_negate_overflow(void) +{ + volatile int val = INT_MIN; + + UBSAN_TEST(CONFIG_UBSAN_SIGNED_WRAP); + val = -val; +} + static void test_ubsan_divrem_overflow(void) { volatile int val = 16; @@ -90,6 +123,10 @@ static void test_ubsan_misaligned_access(void) } static const test_ubsan_fp test_ubsan_array[] = { + test_ubsan_add_overflow, + test_ubsan_sub_overflow, + test_ubsan_mul_overflow, + test_ubsan_negate_overflow, test_ubsan_shift_out_of_bounds, test_ubsan_out_of_bounds, test_ubsan_load_invalid_value, diff --git a/lib/ubsan.c b/lib/ubsan.c index df4f8d1354bb..5fc107f61934 100644 --- a/lib/ubsan.c +++ b/lib/ubsan.c @@ -222,6 +222,74 @@ static void ubsan_epilogue(void) check_panic_on_warn("UBSAN"); } +static void handle_overflow(struct overflow_data *data, void *lhs, + void *rhs, char op) +{ + + struct type_descriptor *type = data->type; + char lhs_val_str[VALUE_LENGTH]; + char rhs_val_str[VALUE_LENGTH]; + + if (suppress_report(&data->location)) + return; + + ubsan_prologue(&data->location, type_is_signed(type) ? + "signed-integer-overflow" : + "unsigned-integer-overflow"); + + val_to_string(lhs_val_str, sizeof(lhs_val_str), type, lhs); + val_to_string(rhs_val_str, sizeof(rhs_val_str), type, rhs); + pr_err("%s %c %s cannot be represented in type %s\n", + lhs_val_str, + op, + rhs_val_str, + type->type_name); + + ubsan_epilogue(); +} + +void __ubsan_handle_add_overflow(void *data, + void *lhs, void *rhs) +{ + + handle_overflow(data, lhs, rhs, '+'); +} +EXPORT_SYMBOL(__ubsan_handle_add_overflow); + +void __ubsan_handle_sub_overflow(void *data, + void *lhs, void *rhs) +{ + handle_overflow(data, lhs, rhs, '-'); +} +EXPORT_SYMBOL(__ubsan_handle_sub_overflow); + +void __ubsan_handle_mul_overflow(void *data, + void *lhs, void *rhs) +{ + handle_overflow(data, lhs, rhs, '*'); +} +EXPORT_SYMBOL(__ubsan_handle_mul_overflow); + +void __ubsan_handle_negate_overflow(void *_data, void *old_val) +{ + struct overflow_data *data = _data; + char old_val_str[VALUE_LENGTH]; + + if (suppress_report(&data->location)) + return; + + ubsan_prologue(&data->location, "negation-overflow"); + + val_to_string(old_val_str, sizeof(old_val_str), data->type, old_val); + + pr_err("negation of %s cannot be represented in type %s:\n", + old_val_str, data->type->type_name); + + ubsan_epilogue(); +} +EXPORT_SYMBOL(__ubsan_handle_negate_overflow); + + void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs) { struct overflow_data *data = _data; diff --git a/lib/ubsan.h b/lib/ubsan.h index 5d99ab81913b..0abbbac8700d 100644 --- a/lib/ubsan.h +++ b/lib/ubsan.h @@ -124,6 +124,10 @@ typedef s64 s_max; typedef u64 u_max; #endif +void __ubsan_handle_add_overflow(void *data, void *lhs, void *rhs); +void __ubsan_handle_sub_overflow(void *data, void *lhs, void *rhs); +void __ubsan_handle_mul_overflow(void *data, void *lhs, void *rhs); +void __ubsan_handle_negate_overflow(void *_data, void *old_val); void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs); void __ubsan_handle_type_mismatch(struct type_mismatch_data *data, void *ptr); void __ubsan_handle_type_mismatch_v1(void *_data, void *ptr); diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 52efc520ae4f..7ce8ecccc65a 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -177,6 +177,9 @@ ifeq ($(CONFIG_UBSAN),y) _c_flags += $(if $(patsubst n%,, \ $(UBSAN_SANITIZE_$(basetarget).o)$(UBSAN_SANITIZE)y), \ $(CFLAGS_UBSAN)) +_c_flags += $(if $(patsubst n%,, \ + $(UBSAN_WRAP_SIGNED_$(basetarget).o)$(UBSAN_SANITIZE_$(basetarget).o)$(UBSAN_WRAP_SIGNED)$(UBSAN_SANITIZE)y), \ + $(CFLAGS_UBSAN_WRAP_SIGNED)) endif ifeq ($(CONFIG_KCOV),y) diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan index 7cf42231042b..bc957add0b4d 100644 --- a/scripts/Makefile.ubsan +++ b/scripts/Makefile.ubsan @@ -13,3 +13,6 @@ ubsan-cflags-$(CONFIG_UBSAN_ENUM) += -fsanitize=enum ubsan-cflags-$(CONFIG_UBSAN_TRAP) += $(call cc-option,-fsanitize-trap=undefined,-fsanitize-undefined-trap-on-error) export CFLAGS_UBSAN := $(ubsan-cflags-y) + +ubsan-wrap-signed-cflags-$(CONFIG_UBSAN_SIGNED_WRAP) += -fsanitize=signed-integer-overflow +export CFLAGS_UBSAN_WRAP_SIGNED := $(ubsan-wrap-signed-cflags-y) -- 2.34.1