[v5] overflow: Introduce overflows_type() and castable_to_type()

  From: Kees Cook <keescook@chromium.org>

Implement a robust overflows_type() macro to test if a variable or
constant value would overflow another variable or type. This can be
used as a constant expression for static_assert() (which requires a
constant expression[1][2]) when used on constant values. This must be
constructed manually, since __builtin_add_overflow() does not produce
a constant expression[3].

Additionally adds castable_to_type(), similar to __same_type(), but for
checking if a constant value would overflow if cast to a given type.

Add unit tests for overflows_type(), __same_type(), and castable_to_type()
to the existing KUnit "overflow" test.

[1] https://en.cppreference.com/w/c/language/_Static_assert
[2] C11 standard (ISO/IEC 9899:2011): 6.7.10 Static assertions
[3] https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html
    6.56 Built-in Functions to Perform Arithmetic with Overflow Checking
    Built-in Function: bool __builtin_add_overflow (type1 a, type2 b,

Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Tom Rix <trix@redhat.com>
Cc: Daniel Latypov <dlatypov@google.com>
Cc: Vitor Massaru Iha <vitor@massaru.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-hardening@vger.kernel.org
Cc: llvm@lists.linux.dev
Co-developed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
v5: drop the cc-disable-warning and just disable the warning directly (Nathan)
v4:
 - move version v2 changelog commit message to under the --- marker (Mauro)
 - remove the #pragma addition in the code and modify the Makefile to handle the
   same feature (Jani)
v3:
 - chagne to use uintptr_t type when checking for overflow of pointer type
   variable
v2:
 - fix comment typo
 - wrap clang pragma to avoid GCC warnings
 - style nit cleanups
 - rename __castable_to_type() to castable_to_type()
 - remove prior overflows_type() definition
v1: https://lore.kernel.org/lkml/20220926003743.409911-1-keescook@chromium.org
---
 drivers/gpu/drm/i915/i915_user_extensions.c |   2 +-
 drivers/gpu/drm/i915/i915_utils.h           |   4 -
 include/linux/compiler.h                    |   1 +
 include/linux/overflow.h                    |  48 +++
 lib/Makefile                                |   4 +
 lib/overflow_kunit.c                        | 383 +++++++++++++++++++-
 6 files changed, 436 insertions(+), 6 deletions(-)
  

Hi Kees,

I've updated to v5 with the last comment of Nathan.
Could you please kindly review what more is needed as we move forward 
with this patch?

Br,

G.G.

On 10/24/22 11:11 PM, Gwan-gyeong Mun wrote:
> From: Kees Cook <keescook@chromium.org>
> 
> Implement a robust overflows_type() macro to test if a variable or
> constant value would overflow another variable or type. This can be
> used as a constant expression for static_assert() (which requires a
> constant expression[1][2]) when used on constant values. This must be
> constructed manually, since __builtin_add_overflow() does not produce
> a constant expression[3].
> 
> Additionally adds castable_to_type(), similar to __same_type(), but for
> checking if a constant value would overflow if cast to a given type.
> 
> Add unit tests for overflows_type(), __same_type(), and castable_to_type()
> to the existing KUnit "overflow" test.
> 
> [1] https://en.cppreference.com/w/c/language/_Static_assert
> [2] C11 standard (ISO/IEC 9899:2011): 6.7.10 Static assertions
> [3] https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html
>      6.56 Built-in Functions to Perform Arithmetic with Overflow Checking
>      Built-in Function: bool __builtin_add_overflow (type1 a, type2 b,
> 
> Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Tom Rix <trix@redhat.com>
> Cc: Daniel Latypov <dlatypov@google.com>
> Cc: Vitor Massaru Iha <vitor@massaru.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Cc: llvm@lists.linux.dev
> Co-developed-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v5: drop the cc-disable-warning and just disable the warning directly (Nathan)
> v4:
>   - move version v2 changelog commit message to under the --- marker (Mauro)
>   - remove the #pragma addition in the code and modify the Makefile to handle the
>     same feature (Jani)
> v3:
>   - chagne to use uintptr_t type when checking for overflow of pointer type
>     variable
> v2:
>   - fix comment typo
>   - wrap clang pragma to avoid GCC warnings
>   - style nit cleanups
>   - rename __castable_to_type() to castable_to_type()
>   - remove prior overflows_type() definition
> v1: https://lore.kernel.org/lkml/20220926003743.409911-1-keescook@chromium.org
> ---
>   drivers/gpu/drm/i915/i915_user_extensions.c |   2 +-
>   drivers/gpu/drm/i915/i915_utils.h           |   4 -
>   include/linux/compiler.h                    |   1 +
>   include/linux/overflow.h                    |  48 +++
>   lib/Makefile                                |   4 +
>   lib/overflow_kunit.c                        | 383 +++++++++++++++++++-
>   6 files changed, 436 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c b/drivers/gpu/drm/i915/i915_user_extensions.c
> index c822d0aafd2d..e3f808372c47 100644
> --- a/drivers/gpu/drm/i915/i915_user_extensions.c
> +++ b/drivers/gpu/drm/i915/i915_user_extensions.c
> @@ -51,7 +51,7 @@ int i915_user_extensions(struct i915_user_extension __user *ext,
>   			return err;
>   
>   		if (get_user(next, &ext->next_extension) ||
> -		    overflows_type(next, ext))
> +		    overflows_type(next, uintptr_t))
>   			return -EFAULT;
>   
>   		ext = u64_to_user_ptr(next);
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index 6c14d13364bf..67a66d4d5c70 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -111,10 +111,6 @@ bool i915_error_injected(void);
>   #define range_overflows_end_t(type, start, size, max) \
>   	range_overflows_end((type)(start), (type)(size), (type)(max))
>   
> -/* Note we don't consider signbits :| */
> -#define overflows_type(x, T) \
> -	(sizeof(x) > sizeof(T) && (x) >> BITS_PER_TYPE(T))
> -
>   #define ptr_mask_bits(ptr, n) ({					\
>   	unsigned long __v = (unsigned long)(ptr);			\
>   	(typeof(ptr))(__v & -BIT(n));					\
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 973a1bfd7ef5..947a60b801db 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -236,6 +236,7 @@ static inline void *offset_to_ptr(const int *off)
>    * bool and also pointer types.
>    */
>   #define is_signed_type(type) (((type)(-1)) < (__force type)1)
> +#define is_unsigned_type(type) (!is_signed_type(type))
>   
>   /*
>    * This is needed in functions which generate the stack canary, see
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 19dfdd74835e..58eb34aa2af9 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -127,6 +127,54 @@ static inline bool __must_check __must_check_overflow(bool overflow)
>   	(*_d >> _to_shift) != _a);					\
>   }))
>   
> +#define __overflows_type_constexpr(x, T) (			\
> +	is_unsigned_type(typeof(x)) ?				\
> +		(x) > type_max(typeof(T)) ? 1 : 0		\
> +	: is_unsigned_type(typeof(T)) ?				\
> +		(x) < 0 || (x) > type_max(typeof(T)) ? 1 : 0	\
> +		: (x) < type_min(typeof(T)) ||			\
> +		  (x) > type_max(typeof(T)) ? 1 : 0)
> +
> +#define __overflows_type(x, T)		({	\
> +	typeof(T) v = 0;			\
> +	check_add_overflow((x), v, &v);		\
> +})
> +
> +/**
> + * overflows_type - helper for checking the overflows between value, variables,
> + *		    or data type
> + *
> + * @n: source constant value or variable to be checked
> + * @T: destination variable or data type proposed to store @x
> + *
> + * Compares the @x expression for whether or not it can safely fit in
> + * the storage of the type in @T. @x and @T can have different types.
> + * If @x is a constant expression, this will also resolve to a constant
> + * expression.
> + *
> + * Returns: true if overflow can occur, false otherwise.
> + */
> +#define overflows_type(n, T)					\
> +	__builtin_choose_expr(__is_constexpr(n),		\
> +			      __overflows_type_constexpr(n, T),	\
> +			      __overflows_type(n, T))
> +
> +/**
> + * castable_to_type - like __same_type(), but also allows for casted literals
> + *
> + * @n: variable or constant value
> + * @T: variable or data type
> + *
> + * Unlike the __same_type() macro, this allows a constant value as the
> + * first argument. If this value would not overflow into an assignment
> + * of the second argument's type, it returns true. Otherwise, this falls
> + * back to __same_type().
> + */
> +#define castable_to_type(n, T)						\
> +	__builtin_choose_expr(__is_constexpr(n),			\
> +			      !__overflows_type_constexpr(n, T),	\
> +			      __same_type(n, T))
> +
>   /**
>    * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX
>    *
> diff --git a/lib/Makefile b/lib/Makefile
> index 161d6a724ff7..583daefe4ac1 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -376,6 +376,10 @@ obj-$(CONFIG_CMDLINE_KUNIT_TEST) += cmdline_kunit.o
>   obj-$(CONFIG_SLUB_KUNIT_TEST) += slub_kunit.o
>   obj-$(CONFIG_MEMCPY_KUNIT_TEST) += memcpy_kunit.o
>   obj-$(CONFIG_IS_SIGNED_TYPE_KUNIT_TEST) += is_signed_type_kunit.o
> +# We're expecting to do a lot of "always true" or "always false" tests.
> +ifdef CONFIG_CC_IS_CLANG
> +CFLAGS_overflow_kunit.o += -Wno-tautological-constant-out-of-range-compare
> +endif
>   obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o
>   CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable)
>   obj-$(CONFIG_STACKINIT_KUNIT_TEST) += stackinit_kunit.o
> diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
> index 5369634701fa..edd3baf1fe6f 100644
> --- a/lib/overflow_kunit.c
> +++ b/lib/overflow_kunit.c
> @@ -246,7 +246,7 @@ DEFINE_TEST_ARRAY(s64) = {
>   
>   #define DEFINE_TEST_FUNC_TYPED(n, t, fmt)				\
>   static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \
> -{							   		\
> +{									\
>   	check_one_op(t, fmt, add, "+", p->a, p->b, p->sum, p->s_of);	\
>   	check_one_op(t, fmt, add, "+", p->b, p->a, p->sum, p->s_of);	\
>   	check_one_op(t, fmt, sub, "-", p->a, p->b, p->diff, p->d_of);	\
> @@ -708,6 +708,384 @@ static void overflow_size_helpers_test(struct kunit *test)
>   #undef check_one_size_helper
>   }
>   
> +static void overflows_type_test(struct kunit *test)
> +{
> +	int count = 0;
> +	unsigned int var;
> +
> +#define __TEST_OVERFLOWS_TYPE(func, arg1, arg2, of)	do {		\
> +	bool __of = func(arg1, arg2);					\
> +	KUNIT_EXPECT_EQ_MSG(test, __of, of,				\
> +		"expected " #func "(" #arg1 ", " #arg2 " to%s overflow\n",\
> +		of ? "" : " not");					\
> +	count++;							\
> +} while (0)
> +
> +/* Args are: first type, second type, value, overflow expected */
> +#define TEST_OVERFLOWS_TYPE(__t1, __t2, v, of) do {			\
> +	__t1 t1 = (v);							\
> +	__t2 t2;							\
> +	__TEST_OVERFLOWS_TYPE(__overflows_type, t1, t2, of);		\
> +	__TEST_OVERFLOWS_TYPE(__overflows_type, t1, __t2, of);		\
> +	__TEST_OVERFLOWS_TYPE(__overflows_type_constexpr, t1, t2, of);	\
> +	__TEST_OVERFLOWS_TYPE(__overflows_type_constexpr, t1, __t2, of);\
> +} while (0)
> +
> +	TEST_OVERFLOWS_TYPE(u8, u8, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u8, u16, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u8, s8, U8_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u8, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u8, s8, (u8)S8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u8, s16, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s8, u8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s8, u8, -1, true);
> +	TEST_OVERFLOWS_TYPE(s8, u8, S8_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s8, u16, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s8, u16, -1, true);
> +	TEST_OVERFLOWS_TYPE(s8, u16, S8_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s8, u32, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s8, u32, -1, true);
> +	TEST_OVERFLOWS_TYPE(s8, u32, S8_MIN, true);
> +#if BITS_PER_LONG == 64
> +	TEST_OVERFLOWS_TYPE(s8, u64, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s8, u64, -1, true);
> +	TEST_OVERFLOWS_TYPE(s8, u64, S8_MIN, true);
> +#endif
> +	TEST_OVERFLOWS_TYPE(s8, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s8, s8, S8_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s8, s16, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s8, s16, S8_MIN, false);
> +	TEST_OVERFLOWS_TYPE(u16, u8, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u16, u8, (u16)U8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u16, u8, U16_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u16, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u16, s8, (u16)S8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u16, s8, U16_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u16, s16, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u16, s16, (u16)S16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u16, s16, U16_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u16, u32, U16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u16, s32, U16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, u8, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, u8, (s16)U8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s16, u8, -1, true);
> +	TEST_OVERFLOWS_TYPE(s16, u8, S16_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s16, u16, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, u16, -1, true);
> +	TEST_OVERFLOWS_TYPE(s16, u16, S16_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s16, u32, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, u32, -1, true);
> +	TEST_OVERFLOWS_TYPE(s16, u32, S16_MIN, true);
> +#if BITS_PER_LONG == 64
> +	TEST_OVERFLOWS_TYPE(s16, u64, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, u64, -1, true);
> +	TEST_OVERFLOWS_TYPE(s16, u64, S16_MIN, true);
> +#endif
> +	TEST_OVERFLOWS_TYPE(s16, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, s8, S8_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s16, s8, (s16)S8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s16, s8, (s16)S8_MIN - 1, true);
> +	TEST_OVERFLOWS_TYPE(s16, s8, S16_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s16, s8, S16_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s16, s16, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, s16, S16_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s16, s32, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s16, s32, S16_MIN, false);
> +	TEST_OVERFLOWS_TYPE(u32, u8, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u32, u8, (u32)U8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u32, u8, U32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u32, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u32, s8, (u32)S8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u32, s8, U32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u32, u16, U16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u32, u16, U16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u32, u16, U32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u32, s16, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u32, s16, (u32)S16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u32, s16, U32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u32, u32, U32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u32, s32, S32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u32, s32, U32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u32, s32, (u32)S32_MAX + 1, true);
> +#if BITS_PER_LONG == 64
> +	TEST_OVERFLOWS_TYPE(u32, u64, U32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u32, s64, U32_MAX, false);
> +#endif
> +	TEST_OVERFLOWS_TYPE(s32, u8, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, u8, (s32)U8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s32, u16, S32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s32, u8, -1, true);
> +	TEST_OVERFLOWS_TYPE(s32, u8, S32_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s32, u16, U16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, u16, (s32)U16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s32, u16, S32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s32, u16, -1, true);
> +	TEST_OVERFLOWS_TYPE(s32, u16, S32_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s32, u32, S32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, u32, -1, true);
> +	TEST_OVERFLOWS_TYPE(s32, u32, S32_MIN, true);
> +#if BITS_PER_LONG == 64
> +	TEST_OVERFLOWS_TYPE(s32, u64, S32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, u64, -1, true);
> +	TEST_OVERFLOWS_TYPE(s32, u64, S32_MIN, true);
> +#endif
> +	TEST_OVERFLOWS_TYPE(s32, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, s8, S8_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s32, s8, (s32)S8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s32, s8, (s32)S8_MIN - 1, true);
> +	TEST_OVERFLOWS_TYPE(s32, s8, S32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s32, s8, S32_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s32, s16, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, s16, S16_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s32, s16, (s32)S16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s32, s16, (s32)S16_MIN - 1, true);
> +	TEST_OVERFLOWS_TYPE(s32, s16, S32_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s32, s16, S32_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s32, s32, S32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, s32, S32_MIN, false);
> +#if BITS_PER_LONG == 64
> +	TEST_OVERFLOWS_TYPE(s32, s64, S32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s32, s64, S32_MIN, false);
> +	TEST_OVERFLOWS_TYPE(u64, u8, U64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u64, u8, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, u8, (u64)U8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u64, u16, U64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u64, u16, U16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, u16, (u64)U16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u64, u32, U64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u64, u32, U32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, u32, (u64)U32_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u64, u64, U64_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, s8, (u64)S8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u64, s8, U64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u64, s16, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, s16, (u64)S16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u64, s16, U64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u64, s32, S32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, s32, (u64)S32_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(u64, s32, U64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u64, s64, S64_MAX, false);
> +	TEST_OVERFLOWS_TYPE(u64, s64, U64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(u64, s64, (u64)S64_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, u8, S64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s64, u8, S64_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s64, u8, -1, true);
> +	TEST_OVERFLOWS_TYPE(s64, u8, U8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, u8, (s64)U8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, u16, S64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s64, u16, S64_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s64, u16, -1, true);
> +	TEST_OVERFLOWS_TYPE(s64, u16, U16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, u16, (s64)U16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, u32, S64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s64, u32, S64_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s64, u32, -1, true);
> +	TEST_OVERFLOWS_TYPE(s64, u32, U32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, u32, (s64)U32_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, u64, S64_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, u64, S64_MIN, true);
> +	TEST_OVERFLOWS_TYPE(s64, u64, -1, true);
> +	TEST_OVERFLOWS_TYPE(s64, s8, S8_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, s8, S8_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s64, s8, (s64)S8_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, s8, (s64)S8_MIN - 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, s8, S64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s64, s16, S16_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, s16, S16_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s64, s16, (s64)S16_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, s16, (s64)S16_MIN - 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, s16, S64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s64, s32, S32_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, s32, S32_MIN, false);
> +	TEST_OVERFLOWS_TYPE(s64, s32, (s64)S32_MAX + 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, s32, (s64)S32_MIN - 1, true);
> +	TEST_OVERFLOWS_TYPE(s64, s32, S64_MAX, true);
> +	TEST_OVERFLOWS_TYPE(s64, s64, S64_MAX, false);
> +	TEST_OVERFLOWS_TYPE(s64, s64, S64_MIN, false);
> +#endif
> +
> +	/* Check for macro side-effects. */
> +	var = INT_MAX - 1;
> +	__TEST_OVERFLOWS_TYPE(__overflows_type, var++, int, false);
> +	__TEST_OVERFLOWS_TYPE(__overflows_type, var++, int, false);
> +	__TEST_OVERFLOWS_TYPE(__overflows_type, var++, int, true);
> +	var = INT_MAX - 1;
> +	__TEST_OVERFLOWS_TYPE(overflows_type, var++, int, false);
> +	__TEST_OVERFLOWS_TYPE(overflows_type, var++, int, false);
> +	__TEST_OVERFLOWS_TYPE(overflows_type, var++, int, true);
> +
> +	kunit_info(test, "%d overflows_type() tests finished\n", count);
> +#undef TEST_OVERFLOWS_TYPE
> +#undef __TEST_OVERFLOWS_TYPE
> +}
> +
> +static void same_type_test(struct kunit *test)
> +{
> +	int count = 0;
> +	int var;
> +
> +#define TEST_SAME_TYPE(t1, t2, same)			do {	\
> +	typeof(t1) __t1h = type_max(t1);			\
> +	typeof(t1) __t1l = type_min(t1);			\
> +	typeof(t2) __t2h = type_max(t2);			\
> +	typeof(t2) __t2l = type_min(t2);			\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(t1, __t1h));	\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(t1, __t1l));	\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(__t1h, t1));	\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(__t1l, t1));	\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(t2, __t2h));	\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(t2, __t2l));	\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(__t2h, t2));	\
> +	KUNIT_EXPECT_EQ(test, true, __same_type(__t2l, t2));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(t1, t2));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(t2, __t1h));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(t2, __t1l));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(__t1h, t2));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(__t1l, t2));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(t1, __t2h));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(t1, __t2l));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(__t2h, t1));	\
> +	KUNIT_EXPECT_EQ(test, same, __same_type(__t2l, t1));	\
> +} while (0)
> +
> +#if BITS_PER_LONG == 64
> +# define TEST_SAME_TYPE64(base, t, m)	TEST_SAME_TYPE(base, t, m)
> +#else
> +# define TEST_SAME_TYPE64(base, t, m)	do { } while (0)
> +#endif
> +
> +#define TEST_TYPE_SETS(base, mu8, mu16, mu32, ms8, ms16, ms32, mu64, ms64) \
> +do {									\
> +	TEST_SAME_TYPE(base,  u8,  mu8);				\
> +	TEST_SAME_TYPE(base, u16, mu16);				\
> +	TEST_SAME_TYPE(base, u32, mu32);				\
> +	TEST_SAME_TYPE(base,  s8,  ms8);				\
> +	TEST_SAME_TYPE(base, s16, ms16);				\
> +	TEST_SAME_TYPE(base, s32, ms32);				\
> +	TEST_SAME_TYPE64(base, u64, mu64);				\
> +	TEST_SAME_TYPE64(base, s64, ms64);				\
> +} while (0)
> +
> +	TEST_TYPE_SETS(u8,   true, false, false, false, false, false, false, false);
> +	TEST_TYPE_SETS(u16, false,  true, false, false, false, false, false, false);
> +	TEST_TYPE_SETS(u32, false, false,  true, false, false, false, false, false);
> +	TEST_TYPE_SETS(s8,  false, false, false,  true, false, false, false, false);
> +	TEST_TYPE_SETS(s16, false, false, false, false,  true, false, false, false);
> +	TEST_TYPE_SETS(s32, false, false, false, false, false,  true, false, false);
> +#if BITS_PER_LONG == 64
> +	TEST_TYPE_SETS(u64, false, false, false, false, false, false,  true, false);
> +	TEST_TYPE_SETS(s64, false, false, false, false, false, false, false,  true);
> +#endif
> +
> +	/* Check for macro side-effects. */
> +	var = 4;
> +	KUNIT_EXPECT_EQ(test, var, 4);
> +	KUNIT_EXPECT_TRUE(test, __same_type(var++, int));
> +	KUNIT_EXPECT_EQ(test, var, 4);
> +	KUNIT_EXPECT_TRUE(test, __same_type(int, var++));
> +	KUNIT_EXPECT_EQ(test, var, 4);
> +	KUNIT_EXPECT_TRUE(test, __same_type(var++, var++));
> +	KUNIT_EXPECT_EQ(test, var, 4);
> +
> +	kunit_info(test, "%d __same_type() tests finished\n", count);
> +
> +#undef TEST_TYPE_SETS
> +#undef TEST_SAME_TYPE64
> +#undef TEST_SAME_TYPE
> +}
> +
> +static void castable_to_type_test(struct kunit *test)
> +{
> +	int count = 0;
> +
> +#define TEST_CASTABLE_TO_TYPE(arg1, arg2, pass)	do {	\
> +	bool __pass = castable_to_type(arg1, arg2);		\
> +	KUNIT_EXPECT_EQ_MSG(test, __pass, pass,			\
> +		"expected castable_to_type(" #arg1 ", " #arg2 ") to%s pass\n",\
> +		pass ? "" : " not");				\
> +	count++;						\
> +} while (0)
> +
> +	TEST_CASTABLE_TO_TYPE(16, u8, true);
> +	TEST_CASTABLE_TO_TYPE(16, u16, true);
> +	TEST_CASTABLE_TO_TYPE(16, u32, true);
> +	TEST_CASTABLE_TO_TYPE(16, s8, true);
> +	TEST_CASTABLE_TO_TYPE(16, s16, true);
> +	TEST_CASTABLE_TO_TYPE(16, s32, true);
> +	TEST_CASTABLE_TO_TYPE(-16, s8, true);
> +	TEST_CASTABLE_TO_TYPE(-16, s16, true);
> +	TEST_CASTABLE_TO_TYPE(-16, s32, true);
> +#if BITS_PER_LONG == 64
> +	TEST_CASTABLE_TO_TYPE(16, u64, true);
> +	TEST_CASTABLE_TO_TYPE(-16, s64, true);
> +#endif
> +
> +#define TEST_CASTABLE_TO_TYPE_VAR(width)	do {				\
> +	u ## width u ## width ## var = 0;					\
> +	s ## width s ## width ## var = 0;					\
> +										\
> +	/* Constant expressions that fit types. */				\
> +	TEST_CASTABLE_TO_TYPE(type_max(u ## width), u ## width, true);		\
> +	TEST_CASTABLE_TO_TYPE(type_min(u ## width), u ## width, true);		\
> +	TEST_CASTABLE_TO_TYPE(type_max(u ## width), u ## width ## var, true);	\
> +	TEST_CASTABLE_TO_TYPE(type_min(u ## width), u ## width ## var, true);	\
> +	TEST_CASTABLE_TO_TYPE(type_max(s ## width), s ## width, true);		\
> +	TEST_CASTABLE_TO_TYPE(type_min(s ## width), s ## width, true);		\
> +	TEST_CASTABLE_TO_TYPE(type_max(s ## width), s ## width ## var, true);	\
> +	TEST_CASTABLE_TO_TYPE(type_min(u ## width), s ## width ## var, true);	\
> +	/* Constant expressions that do not fit types. */			\
> +	TEST_CASTABLE_TO_TYPE(type_max(u ## width), s ## width, false);		\
> +	TEST_CASTABLE_TO_TYPE(type_max(u ## width), s ## width ## var, false);	\
> +	TEST_CASTABLE_TO_TYPE(type_min(s ## width), u ## width, false);		\
> +	TEST_CASTABLE_TO_TYPE(type_min(s ## width), u ## width ## var, false);	\
> +	/* Non-constant expression with mismatched type. */			\
> +	TEST_CASTABLE_TO_TYPE(s ## width ## var, u ## width, false);		\
> +	TEST_CASTABLE_TO_TYPE(u ## width ## var, s ## width, false);		\
> +} while (0)
> +
> +#define TEST_CASTABLE_TO_TYPE_RANGE(width)	do {				\
> +	unsigned long big = U ## width ## _MAX;					\
> +	signed long small = S ## width ## _MIN;					\
> +	u ## width u ## width ## var = 0;					\
> +	s ## width s ## width ## var = 0;					\
> +										\
> +	/* Constant expression in range. */					\
> +	TEST_CASTABLE_TO_TYPE(U ## width ## _MAX, u ## width, true);		\
> +	TEST_CASTABLE_TO_TYPE(U ## width ## _MAX, u ## width ## var, true);	\
> +	TEST_CASTABLE_TO_TYPE(S ## width ## _MIN, s ## width, true);		\
> +	TEST_CASTABLE_TO_TYPE(S ## width ## _MIN, s ## width ## var, true);	\
> +	/* Constant expression out of range. */					\
> +	TEST_CASTABLE_TO_TYPE((unsigned long)U ## width ## _MAX + 1, u ## width, false); \
> +	TEST_CASTABLE_TO_TYPE((unsigned long)U ## width ## _MAX + 1, u ## width ## var, false); \
> +	TEST_CASTABLE_TO_TYPE((signed long)S ## width ## _MIN - 1, s ## width, false); \
> +	TEST_CASTABLE_TO_TYPE((signed long)S ## width ## _MIN - 1, s ## width ## var, false); \
> +	/* Non-constant expression with mismatched type. */			\
> +	TEST_CASTABLE_TO_TYPE(big, u ## width, false);				\
> +	TEST_CASTABLE_TO_TYPE(big, u ## width ## var, false);			\
> +	TEST_CASTABLE_TO_TYPE(small, s ## width, false);			\
> +	TEST_CASTABLE_TO_TYPE(small, s ## width ## var, false);			\
> +} while (0)
> +
> +	TEST_CASTABLE_TO_TYPE_VAR(8);
> +	TEST_CASTABLE_TO_TYPE_VAR(16);
> +	TEST_CASTABLE_TO_TYPE_VAR(32);
> +#if BITS_PER_LONG == 64
> +	TEST_CASTABLE_TO_TYPE_VAR(64);
> +#endif
> +
> +	TEST_CASTABLE_TO_TYPE_RANGE(8);
> +	TEST_CASTABLE_TO_TYPE_RANGE(16);
> +#if BITS_PER_LONG == 64
> +	TEST_CASTABLE_TO_TYPE_RANGE(32);
> +#endif
> +	kunit_info(test, "%d castable_to_type() tests finished\n", count);
> +
> +#undef TEST_CASTABLE_TO_TYPE_RANGE
> +#undef TEST_CASTABLE_TO_TYPE_VAR
> +#undef TEST_CASTABLE_TO_TYPE
> +}
> +
>   static struct kunit_case overflow_test_cases[] = {
>   	KUNIT_CASE(u8_u8__u8_overflow_test),
>   	KUNIT_CASE(s8_s8__s8_overflow_test),
> @@ -730,6 +1108,9 @@ static struct kunit_case overflow_test_cases[] = {
>   	KUNIT_CASE(shift_nonsense_test),
>   	KUNIT_CASE(overflow_allocation_test),
>   	KUNIT_CASE(overflow_size_helpers_test),
> +	KUNIT_CASE(overflows_type_test),
> +	KUNIT_CASE(same_type_test),
> +	KUNIT_CASE(castable_to_type_test),
>   	{}
>   };
>
  

On Sat, Oct 29, 2022 at 08:55:43AM +0300, Gwan-gyeong Mun wrote:
> Hi Kees,

Hi! :)

> I've updated to v5 with the last comment of Nathan.
> Could you please kindly review what more is needed as we move forward with
> this patch?

It looks fine to me -- I assume it'll go via the drm tree? Would you
rather I carry the non-drm changes in my tree instead?

>
  

On 10/29/22 10:32 AM, Kees Cook wrote:
> On Sat, Oct 29, 2022 at 08:55:43AM +0300, Gwan-gyeong Mun wrote:
>> Hi Kees,
> 
> Hi! :)
> 
>> I've updated to v5 with the last comment of Nathan.
>> Could you please kindly review what more is needed as we move forward with
>> this patch?
> 
> It looks fine to me -- I assume it'll go via the drm tree? Would you
> rather I carry the non-drm changes in my tree instead?
> 
Hi!
Yes, I think it would be better to run this patch on your tree.
this patch moves the macro of i915 to overflows.h and modifies one part 
of drm's driver code, but I think this part can be easily applied when 
merging into the drm tree.

Many thanks,
G.G.
>>
  

On Sat, Oct 29, 2022 at 11:01:38AM +0300, Gwan-gyeong Mun wrote:
> 
> 
> On 10/29/22 10:32 AM, Kees Cook wrote:
> > On Sat, Oct 29, 2022 at 08:55:43AM +0300, Gwan-gyeong Mun wrote:
> > > Hi Kees,
> > 
> > Hi! :)
> > 
> > > I've updated to v5 with the last comment of Nathan.
> > > Could you please kindly review what more is needed as we move forward with
> > > this patch?
> > 
> > It looks fine to me -- I assume it'll go via the drm tree? Would you
> > rather I carry the non-drm changes in my tree instead?
> > 
> Hi!
> Yes, I think it would be better to run this patch on your tree.
> this patch moves the macro of i915 to overflows.h and modifies one part of
> drm's driver code, but I think this part can be easily applied when merging
> into the drm tree.

I've rebased it to the hardening tree, and it should appear in -next
shortly:

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=for-next/hardening&id=5904fcb776d0b518be96bca43f258db90f26ba9a
  

On 11/2/22 1:06 AM, Kees Cook wrote:
> On Sat, Oct 29, 2022 at 11:01:38AM +0300, Gwan-gyeong Mun wrote:
>>
>>
>> On 10/29/22 10:32 AM, Kees Cook wrote:
>>> On Sat, Oct 29, 2022 at 08:55:43AM +0300, Gwan-gyeong Mun wrote:
>>>> Hi Kees,
>>>
>>> Hi! :)
>>>
>>>> I've updated to v5 with the last comment of Nathan.
>>>> Could you please kindly review what more is needed as we move forward with
>>>> this patch?
>>>
>>> It looks fine to me -- I assume it'll go via the drm tree? Would you
>>> rather I carry the non-drm changes in my tree instead?
>>>
>> Hi!
>> Yes, I think it would be better to run this patch on your tree.
>> this patch moves the macro of i915 to overflows.h and modifies one part of
>> drm's driver code, but I think this part can be easily applied when merging
>> into the drm tree.
> 
> I've rebased it to the hardening tree, and it should appear in -next
> shortly:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=for-next/hardening&id=5904fcb776d0b518be96bca43f258db90f26ba9a
> 
Thanks for making this patch go forward.

G.G.
  

On 24/10/2022 22.11, Gwan-gyeong Mun wrote:
> From: Kees Cook <keescook@chromium.org>
> 
> Implement a robust overflows_type() macro to test if a variable or
> constant value would overflow another variable or type. This can be
> used as a constant expression for static_assert() (which requires a
> constant expression[1][2]) when used on constant values. This must be
> constructed manually, since __builtin_add_overflow() does not produce
> a constant expression[3].
> 
> Additionally adds castable_to_type(), similar to __same_type(), but for
> checking if a constant value would overflow if cast to a given type.
> 

> +#define __overflows_type_constexpr(x, T) (			\
> +	is_unsigned_type(typeof(x)) ?				\
> +		(x) > type_max(typeof(T)) ? 1 : 0		\
> +	: is_unsigned_type(typeof(T)) ?				\
> +		(x) < 0 || (x) > type_max(typeof(T)) ? 1 : 0	\
> +		: (x) < type_min(typeof(T)) ||			\
> +		  (x) > type_max(typeof(T)) ? 1 : 0)
> +

Can't all these instances of "foo ? 1 : 0" be simplified to "foo"? That
would improve the readability of this thing somewhat IMO.

Rasmus
  

On Wed, Nov 02, 2022 at 12:52:32PM +0100, Rasmus Villemoes wrote:
> On 24/10/2022 22.11, Gwan-gyeong Mun wrote:
> > From: Kees Cook <keescook@chromium.org>
> > 
> > Implement a robust overflows_type() macro to test if a variable or
> > constant value would overflow another variable or type. This can be
> > used as a constant expression for static_assert() (which requires a
> > constant expression[1][2]) when used on constant values. This must be
> > constructed manually, since __builtin_add_overflow() does not produce
> > a constant expression[3].
> > 
> > Additionally adds castable_to_type(), similar to __same_type(), but for
> > checking if a constant value would overflow if cast to a given type.
> > 
> 
> > +#define __overflows_type_constexpr(x, T) (			\
> > +	is_unsigned_type(typeof(x)) ?				\
> > +		(x) > type_max(typeof(T)) ? 1 : 0		\
> > +	: is_unsigned_type(typeof(T)) ?				\
> > +		(x) < 0 || (x) > type_max(typeof(T)) ? 1 : 0	\
> > +		: (x) < type_min(typeof(T)) ||			\
> > +		  (x) > type_max(typeof(T)) ? 1 : 0)
> > +
> 
> Can't all these instances of "foo ? 1 : 0" be simplified to "foo"? That
> would improve the readability of this thing somewhat IMO.

Oh, good point. :P I'll fix these.