include/linux/overflow.h - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0 OR MIT */
 #ifndef __LINUX_OVERFLOW_H
 #define __LINUX_OVERFLOW_H

 #include <linux/compiler.h>
 #include <linux/limits.h>

 /*
  * We need to compute the minimum and maximum values representable in a given
  * type. These macros may also be useful elsewhere. It would seem more obvious
  * to do something like:
  *
  * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
  * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
  *
  * Unfortunately, the middle expressions, strictly speaking, have
  * undefined behaviour, and at least some versions of gcc warn about
  * the type_max expression (but not if -fsanitize=undefined is in
  * effect; in that case, the warning is deferred to runtime...).
  *
  * The slightly excessive casting in type_min is to make sure the
  * macros also produce sensible values for the exotic type _Bool. [The
  * overflow checkers only almost work for _Bool, but that's
  * a-feature-not-a-bug, since people shouldn't be doing arithmetic on
  * _Bools. Besides, the gcc builtins don't allow _Bool* as third
  * argument.]
  *
  * Idea stolen from
  * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -
  * credit to Christian Biere.
  */
 #define is_signed_type(type)       (((type)(-1)) < (type)1)
 #define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
 #define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
 #define type_min(T) ((T)((T)-type_max(T)-(T)1))

 /*
  * Avoids triggering -Wtype-limits compilation warning,
  * while using unsigned data types to check a < 0.
  */
 #define is_non_negative(a) ((a) > 0 || (a) == 0)
 #define is_negative(a) (!(is_non_negative(a)))

 /*
  * Allows for effectively applying __must_check to a macro so we can have
  * both the type-agnostic benefits of the macros while also being able to
  * enforce that the return value is, in fact, checked.
  */
 static inline bool __must_check __must_check_overflow(bool overflow)
 {
 	return unlikely(overflow);
 }

 /*
  * For simplicity and code hygiene, the fallback code below insists on
  * a, b and *d having the same type (similar to the min() and max()
  * macros), whereas gcc's type-generic overflow checkers accept
  * different types. Hence we don't just make check_add_overflow an
  * alias for __builtin_add_overflow, but add type checks similar to
  * below.
  */
 #define check_add_overflow(a, b, d) __must_check_overflow(({	\
 	typeof(a) __a = (a);			\
 	typeof(b) __b = (b);			\
 	typeof(d) __d = (d);			\
 	(void) (&__a == &__b);			\
 	(void) (&__a == __d);			\
 	__builtin_add_overflow(__a, __b, __d);	\
 }))

 #define check_sub_overflow(a, b, d) __must_check_overflow(({	\
 	typeof(a) __a = (a);			\
 	typeof(b) __b = (b);			\
 	typeof(d) __d = (d);			\
 	(void) (&__a == &__b);			\
 	(void) (&__a == __d);			\
 	__builtin_sub_overflow(__a, __b, __d);	\
 }))

 #define check_mul_overflow(a, b, d) __must_check_overflow(({	\
 	typeof(a) __a = (a);			\
 	typeof(b) __b = (b);			\
 	typeof(d) __d = (d);			\
 	(void) (&__a == &__b);			\
 	(void) (&__a == __d);			\
 	__builtin_mul_overflow(__a, __b, __d);	\
 }))

 /** check_shl_overflow() - Calculate a left-shifted value and check overflow
  *
  * @a: Value to be shifted
  * @s: How many bits left to shift
  * @d: Pointer to where to store the result
  *
  * Computes *@d = (@a << @s)
  *
  * Returns true if '*d' cannot hold the result or when 'a << s' doesn't
  * make sense. Example conditions:
  * - 'a << s' causes bits to be lost when stored in *d.
  * - 's' is garbage (e.g. negative) or so large that the result of
  *   'a << s' is guaranteed to be 0.
  * - 'a' is negative.
  * - 'a << s' sets the sign bit, if any, in '*d'.
  *
  * '*d' will hold the results of the attempted shift, but is not
  * considered "safe for use" if true is returned.
  */
 #define check_shl_overflow(a, s, d) __must_check_overflow(({		\
 	typeof(a) _a = a;						\
 	typeof(s) _s = s;						\
 	typeof(d) _d = d;						\
 	u64 _a_full = _a;						\
 	unsigned int _to_shift =					\
 		is_non_negative(_s) && _s < 8 * sizeof(*d) ? _s : 0;	\
 	*_d = (_a_full << _to_shift);					\
 	(_to_shift != _s || is_negative(*_d) || is_negative(_a) ||	\
 	(*_d >> _to_shift) != _a);					\
 }))

 /**
  * array_size() - Calculate size of 2-dimensional array.
  *
  * @a: dimension one
  * @b: dimension two
  *
  * Calculates size of 2-dimensional array: @a * @b.
  *
  * Returns: number of bytes needed to represent the array or SIZE_MAX on
  * overflow.
  */
 static inline __must_check size_t array_size(size_t a, size_t b)
 {
 	size_t bytes;

 	if (check_mul_overflow(a, b, &bytes))
 		return SIZE_MAX;

 	return bytes;
 }

 /**
  * array3_size() - Calculate size of 3-dimensional array.
  *
  * @a: dimension one
  * @b: dimension two
  * @c: dimension three
  *
  * Calculates size of 3-dimensional array: @a * @b * @c.
  *
  * Returns: number of bytes needed to represent the array or SIZE_MAX on
  * overflow.
  */
 static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)
 {
 	size_t bytes;

 	if (check_mul_overflow(a, b, &bytes))
 		return SIZE_MAX;
 	if (check_mul_overflow(bytes, c, &bytes))
 		return SIZE_MAX;

 	return bytes;
 }

 /*
  * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
  * struct_size() below.
  */
 static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
 {
 	size_t bytes;

 	if (check_mul_overflow(a, b, &bytes))
 		return SIZE_MAX;
 	if (check_add_overflow(bytes, c, &bytes))
 		return SIZE_MAX;

 	return bytes;
 }

 /**
  * struct_size() - Calculate size of structure with trailing array.
  * @p: Pointer to the structure.
  * @member: Name of the array member.
  * @count: Number of elements in the array.
  *
  * Calculates size of memory needed for structure @p followed by an
  * array of @count number of @member elements.
  *
  * Return: number of bytes needed or SIZE_MAX on overflow.
  */
 #define struct_size(p, member, count)					\
 	__ab_c_size(count,						\
 		    sizeof(*(p)->member) + __must_be_array((p)->member),\
 		    sizeof(*(p)))

 /**
  * flex_array_size() - Calculate size of a flexible array member
  *                     within an enclosing structure.
  *
  * @p: Pointer to the structure.
  * @member: Name of the flexible array member.
  * @count: Number of elements in the array.
  *
  * Calculates size of a flexible array of @count number of @member
  * elements, at the end of structure @p.
  *
  * Return: number of bytes needed or SIZE_MAX on overflow.
  */
 #define flex_array_size(p, member, count)				\
 	array_size(count,						\
 		    sizeof(*(p)->member) + __must_be_array((p)->member))

 #endif /* __LINUX_OVERFLOW_H */
	/* SPDX-License-Identifier: GPL-2.0 OR MIT */
	#ifndef __LINUX_OVERFLOW_H
	#define __LINUX_OVERFLOW_H

	#include <linux/compiler.h>
	#include <linux/limits.h>

	/*
	* We need to compute the minimum and maximum values representable in a given
	* type. These macros may also be useful elsewhere. It would seem more obvious
	* to do something like:
	*
	* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
	* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
	*
	* Unfortunately, the middle expressions, strictly speaking, have
	* undefined behaviour, and at least some versions of gcc warn about
	* the type_max expression (but not if -fsanitize=undefined is in
	* effect; in that case, the warning is deferred to runtime...).
	*
	* The slightly excessive casting in type_min is to make sure the
	* macros also produce sensible values for the exotic type _Bool. [The
	* overflow checkers only almost work for _Bool, but that's
	* a-feature-not-a-bug, since people shouldn't be doing arithmetic on
	* _Bools. Besides, the gcc builtins don't allow _Bool* as third
	* argument.]
	*
	* Idea stolen from
	* https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -
	* credit to Christian Biere.
	*/
	#define is_signed_type(type) (((type)(-1)) < (type)1)
	#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
	#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
	#define type_min(T) ((T)((T)-type_max(T)-(T)1))

	/*
	* Avoids triggering -Wtype-limits compilation warning,
	* while using unsigned data types to check a < 0.
	*/
	#define is_non_negative(a) ((a) > 0 \|\| (a) == 0)
	#define is_negative(a) (!(is_non_negative(a)))

	/*
	* Allows for effectively applying __must_check to a macro so we can have
	* both the type-agnostic benefits of the macros while also being able to
	* enforce that the return value is, in fact, checked.
	*/
	static inline bool __must_check __must_check_overflow(bool overflow)
	{
	return unlikely(overflow);
	}

	/*
	* For simplicity and code hygiene, the fallback code below insists on
	* a, b and *d having the same type (similar to the min() and max()
	* macros), whereas gcc's type-generic overflow checkers accept
	* different types. Hence we don't just make check_add_overflow an
	* alias for __builtin_add_overflow, but add type checks similar to
	* below.
	*/
	#define check_add_overflow(a, b, d) __must_check_overflow(({ \
	typeof(a) __a = (a); \
	typeof(b) __b = (b); \
	typeof(d) __d = (d); \
	(void) (&__a == &__b); \
	(void) (&__a == __d); \
	__builtin_add_overflow(__a, __b, __d); \
	}))

	#define check_sub_overflow(a, b, d) __must_check_overflow(({ \
	typeof(a) __a = (a); \
	typeof(b) __b = (b); \
	typeof(d) __d = (d); \
	(void) (&__a == &__b); \
	(void) (&__a == __d); \
	__builtin_sub_overflow(__a, __b, __d); \
	}))

	#define check_mul_overflow(a, b, d) __must_check_overflow(({ \
	typeof(a) __a = (a); \
	typeof(b) __b = (b); \
	typeof(d) __d = (d); \
	(void) (&__a == &__b); \
	(void) (&__a == __d); \
	__builtin_mul_overflow(__a, __b, __d); \
	}))

	/** check_shl_overflow() - Calculate a left-shifted value and check overflow
	*
	* @a: Value to be shifted
	* @s: How many bits left to shift
	* @d: Pointer to where to store the result
	*
	* Computes *@d = (@a << @s)
	*
	* Returns true if '*d' cannot hold the result or when 'a << s' doesn't
	* make sense. Example conditions:
	* - 'a << s' causes bits to be lost when stored in *d.
	* - 's' is garbage (e.g. negative) or so large that the result of
	* 'a << s' is guaranteed to be 0.
	* - 'a' is negative.
	* - 'a << s' sets the sign bit, if any, in '*d'.
	*
	* '*d' will hold the results of the attempted shift, but is not
	* considered "safe for use" if true is returned.
	*/
	#define check_shl_overflow(a, s, d) __must_check_overflow(({ \
	typeof(a) _a = a; \
	typeof(s) _s = s; \
	typeof(d) _d = d; \
	u64 _a_full = _a; \
	unsigned int _to_shift = \
	is_non_negative(_s) && _s < 8 * sizeof(*d) ? _s : 0; \
	*_d = (_a_full << _to_shift); \
	(_to_shift != _s \|\| is_negative(*_d) \|\| is_negative(_a) \|\| \
	(*_d >> _to_shift) != _a); \
	}))

	/**
	* array_size() - Calculate size of 2-dimensional array.
	*
	* @a: dimension one
	* @b: dimension two
	*
	* Calculates size of 2-dimensional array: @a * @b.
	*
	* Returns: number of bytes needed to represent the array or SIZE_MAX on
	* overflow.
	*/
	static inline __must_check size_t array_size(size_t a, size_t b)
	{
	size_t bytes;

	if (check_mul_overflow(a, b, &bytes))
	return SIZE_MAX;

	return bytes;
	}

	/**
	* array3_size() - Calculate size of 3-dimensional array.
	*
	* @a: dimension one
	* @b: dimension two
	* @c: dimension three
	*
	* Calculates size of 3-dimensional array: @a * @b * @c.
	*
	* Returns: number of bytes needed to represent the array or SIZE_MAX on
	* overflow.
	*/
	static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)
	{
	size_t bytes;

	if (check_mul_overflow(a, b, &bytes))
	return SIZE_MAX;
	if (check_mul_overflow(bytes, c, &bytes))
	return SIZE_MAX;

	return bytes;
	}

	/*
	* Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
	* struct_size() below.
	*/
	static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
	{
	size_t bytes;

	if (check_mul_overflow(a, b, &bytes))
	return SIZE_MAX;
	if (check_add_overflow(bytes, c, &bytes))
	return SIZE_MAX;

	return bytes;
	}

	/**
	* struct_size() - Calculate size of structure with trailing array.
	* @p: Pointer to the structure.
	* @member: Name of the array member.
	* @count: Number of elements in the array.
	*
	* Calculates size of memory needed for structure @p followed by an
	* array of @count number of @member elements.
	*
	* Return: number of bytes needed or SIZE_MAX on overflow.
	*/
	#define struct_size(p, member, count) \
	__ab_c_size(count, \
	sizeof(*(p)->member) + __must_be_array((p)->member),\
	sizeof(*(p)))

	/**
	* flex_array_size() - Calculate size of a flexible array member
	* within an enclosing structure.
	*
	* @p: Pointer to the structure.
	* @member: Name of the flexible array member.
	* @count: Number of elements in the array.
	*
	* Calculates size of a flexible array of @count number of @member
	* elements, at the end of structure @p.
	*
	* Return: number of bytes needed or SIZE_MAX on overflow.
	*/
	#define flex_array_size(p, member, count) \
	array_size(count, \
	sizeof(*(p)->member) + __must_be_array((p)->member))

	#endif /* __LINUX_OVERFLOW_H */