Hi,
On Mon, Jan 29, 2024 at 10:00:39AM -0800, Kees Cook wrote:
> Effectively revert commit 6aaa31aeb9cf ("ubsan: remove overflow
> checks"), to allow the kernel to be built with the "overflow"
> sanitizers again. This gives developers a chance to experiment[1][2][3]
> with the instrumentation again, while compilers adjust their sanitizers
> to deal with the impact of -fno-strict-oveflow (i.e. moving from
> "overflow" checking to "wrap-around" checking).
>
> Notably, the naming of the options is adjusted to use the name "WRAP"
> instead of "OVERFLOW". In the strictest sense, arithmetic "overflow"
> happens when a result exceeds the storage of the type, and is considered
> by the C standard and compilers to be undefined behavior for signed
> and pointer types (without -fno-strict-overflow). Unsigned arithmetic
> overflow is defined as always wrapping around.
>
> Because the kernel is built with -fno-strict-overflow, signed and pointer
> arithmetic is defined to always wrap around instead of "overflowing"
> (which could either be elided due to being undefined behavior or would
> wrap around, which led to very weird bugs in the kernel).
>
> So, the config options are added back as CONFIG_UBSAN_SIGNED_WRAP and
> CONFIG_UBSAN_UNSIGNED_WRAP. Since the kernel has several places that
> explicitly depend on wrap-around behavior (e.g. counters, atomics, crypto,
> etc), also introduce the __signed_wrap and __unsigned_wrap function
> attributes for annotating functions where wrapping is expected and should
> not be instrumented. This will allow us to distinguish in the kernel
> between intentional and unintentional cases of arithmetic wrap-around.
>
> Additionally keep these disabled under CONFIG_COMPILE_TEST for now.
This is present in the patch but perhaps its worth noting here that x86
has trouble booting with the unsigned-integer-overflow sanitizer on.
>
> Link: https://github.com/KSPP/linux/issues/26 [1]
> Link: https://github.com/KSPP/linux/issues/27 [2]
> Link: https://github.com/KSPP/linux/issues/344 [3]
> Cc: Justin Stitt <[email protected]>
> Cc: Miguel Ojeda <[email protected]>
> Cc: Nathan Chancellor <[email protected]>
> Cc: Nick Desaulniers <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Marco Elver <[email protected]>
> Cc: Hao Luo <[email protected]>
> Cc: Przemek Kitszel <[email protected]>
> Signed-off-by: Kees Cook <[email protected]>
This patch adheres to the language semantics as I understand them.
Moreover, we would've had to send a patch similar to this once we land
some better sanitizer + -fno-strict-oveflow support in the compilers.
Currently, though, -fsanitize=signed-integer-overflow instruments very
little (if anything at all) due to compiler optimizations in conjunction
with -fno-strict-oveflow. I am working on a new
-fsanitize=signed-integer-wrap in Clang which will instrument more
arithmetic even under -fno-strict-oveflow.
Reviewed-by: Justin Stitt <[email protected]>
> ---
> include/linux/compiler_types.h | 14 ++++++-
> lib/Kconfig.ubsan | 19 ++++++++++
> lib/test_ubsan.c | 49 ++++++++++++++++++++++++
> lib/ubsan.c | 68 ++++++++++++++++++++++++++++++++++
> lib/ubsan.h | 4 ++
> scripts/Makefile.ubsan | 2 +
> 6 files changed, 155 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index 6f1ca49306d2..e585614f3152 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -282,11 +282,23 @@ struct ftrace_likely_data {
> #define __no_sanitize_or_inline __always_inline
> #endif
>
> +/* Allow 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
> +#ifdef CONFIG_UBSAN_UNSIGNED_WRAP
> +# define __unsigned_wrap
> __attribute__((no_sanitize("unsigned-integer-overflow")))
> +#else
> +# define __unsigned_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 __unsigned_wrap
>
> #define noinstr __noinstr_section(".noinstr.text")
>
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 59e21bfec188..a7003e5bd2a1 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -116,6 +116,25 @@ 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.
> +
> +config UBSAN_UNSIGNED_WRAP
> + bool "Perform checking for unsigned arithmetic wrap-around"
> + depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
> + depends on !X86_32 # avoid excessive stack usage on x86-32/clang
> + depends on !COMPILE_TEST
> + help
> + This option enables -fsanitize=unsigned-integer-overflow which checks
> + for wrap-around of any arithmetic operations with unsigned integers.
> This
> + currently causes x86 to fail to boot.
> +
> 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 2062be1f2e80..84d8092d6c32 100644
> --- a/lib/test_ubsan.c
> +++ b/lib/test_ubsan.c
> @@ -11,6 +11,51 @@ 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;
> + volatile unsigned int uval = UINT_MAX;
> +
> + UBSAN_TEST(CONFIG_UBSAN_SIGNED_WRAP);
> + val += 2;
> +
> + UBSAN_TEST(CONFIG_UBSAN_UNSIGNED_WRAP);
> + uval += 2;
> +}
> +
> +static void test_ubsan_sub_overflow(void)
> +{
> + volatile int val = INT_MIN;
> + volatile unsigned int uval = 0;
> + volatile int val2 = 2;
> +
> + UBSAN_TEST(CONFIG_UBSAN_SIGNED_WRAP);
> + val -= val2;
> +
> + UBSAN_TEST(CONFIG_UBSAN_UNSIGNED_WRAP);
> + uval -= val2;
> +}
> +
> +static void test_ubsan_mul_overflow(void)
> +{
> + volatile int val = INT_MAX / 2;
> + volatile unsigned int uval = UINT_MAX / 2;
> +
> + UBSAN_TEST(CONFIG_UBSAN_SIGNED_WRAP);
> + val *= 3;
> +
> + UBSAN_TEST(CONFIG_UBSAN_UNSIGNED_WRAP);
> + uval *= 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 +135,10 @@ 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.ubsan b/scripts/Makefile.ubsan
> index 7cf42231042b..7b2f3d554c59 100644
> --- a/scripts/Makefile.ubsan
> +++ b/scripts/Makefile.ubsan
> @@ -8,6 +8,8 @@ ubsan-cflags-$(CONFIG_UBSAN_LOCAL_BOUNDS) +=
> -fsanitize=local-bounds
> ubsan-cflags-$(CONFIG_UBSAN_SHIFT) += -fsanitize=shift
> ubsan-cflags-$(CONFIG_UBSAN_DIV_ZERO) +=
> -fsanitize=integer-divide-by-zero
> ubsan-cflags-$(CONFIG_UBSAN_UNREACHABLE) += -fsanitize=unreachable
> +ubsan-cflags-$(CONFIG_UBSAN_SIGNED_WRAP) +=
> -fsanitize=signed-integer-overflow
> +ubsan-cflags-$(CONFIG_UBSAN_UNSIGNED_WRAP) +=
> -fsanitize=unsigned-integer-overflow
> ubsan-cflags-$(CONFIG_UBSAN_BOOL) += -fsanitize=bool
> ubsan-cflags-$(CONFIG_UBSAN_ENUM) += -fsanitize=enum
> ubsan-cflags-$(CONFIG_UBSAN_TRAP) += $(call
> cc-option,-fsanitize-trap=undefined,-fsanitize-undefined-trap-on-error)
> --
> 2.34.1
>
Thanks
Justin
