/* SPDX-License-Identifier: GPL-2.0 OR MIT */ #ifndef __LINUX_OVERFLOW_H #define __LINUX_OVERFLOW_H #include <linux/compiler.h> #include <linux/limits.h> #include <linux/const.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 __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_max(t) __type_max(typeof(t)) #define __type_min(T) ((T)((T)-type_max(T)-(T)1)) #define type_min(t) __type_min(typeof(t)) /* * 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 __always_inline bool __must_check __must_check_overflow(bool overflow) { return unlikely(overflow); } /** * check_add_overflow() - Calculate addition with overflow checking * @a: first addend * @b: second addend * @d: pointer to store sum * * Returns true on wrap-around, false otherwise. * * *@d holds the results of the attempted addition, regardless of whether * wrap-around occurred. */ #define check_add_overflow(a, b, d) \ __must_check_overflow(__builtin_add_overflow(a, b, d)) /** * wrapping_add() - Intentionally perform a wrapping addition * @type: type for result of calculation * @a: first addend * @b: second addend * * Return the potentially wrapped-around addition without * tripping any wrap-around sanitizers that may be enabled. */ #define wrapping_add(type, a, b) \ ({ \ type __val; \ __builtin_add_overflow(a, b, &__val); \ __val; \ }) /** * wrapping_assign_add() - Intentionally perform a wrapping increment assignment * @var: variable to be incremented * @offset: amount to add * * Increments @var by @offset with wrap-around. Returns the resulting * value of @var. Will not trip any wrap-around sanitizers. * * Returns the new value of @var. */ #define wrapping_assign_add(var, offset) \ ({ \ typeof(var) *__ptr = &(var); \ *__ptr = wrapping_add(typeof(var), *__ptr, offset); \ }) /** * check_sub_overflow() - Calculate subtraction with overflow checking * @a: minuend; value to subtract from * @b: subtrahend; value to subtract from @a * @d: pointer to store difference * * Returns true on wrap-around, false otherwise. * * *@d holds the results of the attempted subtraction, regardless of whether * wrap-around occurred. */ #define check_sub_overflow(a, b, d) \ __must_check_overflow(__builtin_sub_overflow(a, b, d)) /** * wrapping_sub() - Intentionally perform a wrapping subtraction * @type: type for result of calculation * @a: minuend; value to subtract from * @b: subtrahend; value to subtract from @a * * Return the potentially wrapped-around subtraction without * tripping any wrap-around sanitizers that may be enabled. */ #define wrapping_sub(type, a, b) \ ({ \ type __val; \ __builtin_sub_overflow(a, b, &__val); \ __val; \ }) /** * wrapping_assign_sub() - Intentionally perform a wrapping decrement assign * @var: variable to be decremented * @offset: amount to subtract * * Decrements @var by @offset with wrap-around. Returns the resulting * value of @var. Will not trip any wrap-around sanitizers. * * Returns the new value of @var. */ #define wrapping_assign_sub(var, offset) \ ({ \ typeof(var) *__ptr = &(var); \ *__ptr = wrapping_sub(typeof(var), *__ptr, offset); \ }) /** * check_mul_overflow() - Calculate multiplication with overflow checking * @a: first factor * @b: second factor * @d: pointer to store product * * Returns true on wrap-around, false otherwise. * * *@d holds the results of the attempted multiplication, regardless of whether * wrap-around occurred. */ #define check_mul_overflow(a, b, d) \ __must_check_overflow(__builtin_mul_overflow(a, b, d)) /** * wrapping_mul() - Intentionally perform a wrapping multiplication * @type: type for result of calculation * @a: first factor * @b: second factor * * Return the potentially wrapped-around multiplication without * tripping any wrap-around sanitizers that may be enabled. */ #define wrapping_mul(type, a, b) \ ({ \ type __val; \ __builtin_mul_overflow(a, b, &__val); \ __val; \ }) /** * 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; \ unsigned long long _a_full = _a; \ unsigned int _to_shift = \ _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \ *_d = (_a_full << _to_shift); \ (_to_shift != _s || *_d < 0 || _a < 0 || \ (*_d >> _to_shift) != _a); \ })) #define __overflows_type_constexpr(x, T) ( \ is_unsigned_type(typeof(x)) ? \ (x) > type_max(T) : \ is_unsigned_type(typeof(T)) ? \ (x) < 0 || (x) > type_max(T) : \ (x) < type_min(T) || (x) > type_max(T)) #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)) /** * range_overflows() - Check if a range is out of bounds * @start: Start of the range. * @size: Size of the range. * @max: Exclusive upper boundary. * * A strict check to determine if the range [@start, @start + @size) is * invalid with respect to the allowable range [0, @max). Any range * starting at or beyond @max is considered an overflow, even if @size is 0. * * Returns: true if the range is out of bounds. */ #define range_overflows(start, size, max) ({ \ typeof(start) start__ = (start); \ typeof(size) size__ = (size); \ typeof(max) max__ = (max); \ (void)(&start__ == &size__); \ (void)(&start__ == &max__); \ start__ >= max__ || size__ > max__ - start__; \ }) /** * range_overflows_t() - Check if a range is out of bounds * @type: Data type to use. * @start: Start of the range. * @size: Size of the range. * @max: Exclusive upper boundary. * * Same as range_overflows() but forcing the parameters to @type. * * Returns: true if the range is out of bounds. */ #define range_overflows_t(type, start, size, max) \ range_overflows((type)(start), (type)(size), (type)(max)) /** * range_end_overflows() - Check if a range's endpoint is out of bounds * @start: Start of the range. * @size: Size of the range. * @max: Exclusive upper boundary. * * Checks only if the endpoint of a range (@start + @size) exceeds @max. * Unlike range_overflows(), a zero-sized range at the boundary (@start == @max) * is not considered an overflow. Useful for iterator-style checks. * * Returns: true if the endpoint exceeds the boundary. */ #define range_end_overflows(start, size, max) ({ \ typeof(start) start__ = (start); \ typeof(size) size__ = (size); \ typeof(max) max__ = (max); \ (void)(&start__ == &size__); \ (void)(&start__ == &max__); \ start__ > max__ || size__ > max__ - start__; \ }) /** * range_end_overflows_t() - Check if a range's endpoint is out of bounds * @type: Data type to use. * @start: Start of the range. * @size: Size of the range. * @max: Exclusive upper boundary. * * Same as range_end_overflows() but forcing the parameters to @type. * * Returns: true if the endpoint exceeds the boundary. */ #define range_end_overflows_t(type, start, size, max) \ range_end_overflows((type)(start), (type)(size), (type)(max)) /** * 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 * @factor1: first factor * @factor2: second factor * * Returns: calculate @factor1 * @factor2, both promoted to size_t, * with any overflow causing the return value to be SIZE_MAX. The * lvalue must be size_t to avoid implicit type conversion. */ static __always_inline size_t __must_check size_mul(size_t factor1, size_t factor2) { size_t bytes; if (check_mul_overflow(factor1, factor2, &bytes)) return SIZE_MAX; return bytes; } /** * size_add() - Calculate size_t addition with saturation at SIZE_MAX * @addend1: first addend * @addend2: second addend * * Returns: calculate @addend1 + @addend2, both promoted to size_t, * with any overflow causing the return value to be SIZE_MAX. The * lvalue must be size_t to avoid implicit type conversion. */ static __always_inline size_t __must_check size_add(size_t addend1, size_t addend2) { size_t bytes; if (check_add_overflow(addend1, addend2, &bytes)) return SIZE_MAX; return bytes; } /** * size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX * @minuend: value to subtract from * @subtrahend: value to subtract from @minuend * * Returns: calculate @minuend - @subtrahend, both promoted to size_t, * with any overflow causing the return value to be SIZE_MAX. For * composition with the size_add() and size_mul() helpers, neither * argument may be SIZE_MAX (or the result with be forced to SIZE_MAX). * The lvalue must be size_t to avoid implicit type conversion. */ static __always_inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) { size_t bytes; if (minuend == SIZE_MAX || subtrahend == SIZE_MAX || check_sub_overflow(minuend, subtrahend, &bytes)) return SIZE_MAX; return bytes; } /** * 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. */ #define array_size(a, b) size_mul(a, b) /** * 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. */ #define array3_size(a, b, c) size_mul(size_mul(a, b), c) /** * 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) \ __builtin_choose_expr(__is_constexpr(count), \ (count) * sizeof(*(p)->member) + __must_be_array((p)->member), \ size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member))) /** * struct_size() - Calculate size of structure with trailing flexible 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 of @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) \ __builtin_choose_expr(__is_constexpr(count), \ sizeof(*(p)) + flex_array_size(p, member, count), \ size_add(sizeof(*(p)), flex_array_size(p, member, count))) /** * struct_size_t() - Calculate size of structure with trailing flexible array * @type: structure type name. * @member: Name of the array member. * @count: Number of elements in the array. * * Calculates size of memory needed for structure @type followed by an * array of @count number of @member elements. Prefer using struct_size() * when possible instead, to keep calculations associated with a specific * instance variable of type @type. * * Return: number of bytes needed or SIZE_MAX on overflow. */ #define struct_size_t(type, member, count) \ struct_size((type *)NULL, member, count) /** * struct_offset() - Calculate the offset of a member within a struct * @p: Pointer to the struct * @member: Name of the member to get the offset of * * Calculates the offset of a particular @member of the structure pointed * to by @p. * * Return: number of bytes to the location of @member. */ #define struct_offset(p, member) (offsetof(typeof(*(p)), member)) /** * __DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. * Enables caller macro to pass arbitrary trailing expressions * * @type: structure type name, including "struct" keyword. * @name: Name for a variable to define. * @member: Name of the array member. * @count: Number of elements in the array; must be compile-time const. * @trailer: Trailing expressions for attributes and/or initializers. */ #define __DEFINE_FLEX(type, name, member, count, trailer...) \ _Static_assert(__builtin_constant_p(count), \ "onstack flex array members require compile-time const count"); \ union { \ u8 bytes[struct_size_t(type, member, count)]; \ type obj; \ } name##_u trailer; \ type *name = (type *)&name##_u /** * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. * Enables caller macro to pass (different) initializer. * * @type: structure type name, including "struct" keyword. * @name: Name for a variable to define. * @member: Name of the array member. * @count: Number of elements in the array; must be compile-time const. * @initializer: Initializer expression (e.g., pass `= { }` at minimum). */ #define _DEFINE_FLEX(type, name, member, count, initializer...) \ __DEFINE_FLEX(type, name, member, count, = { .obj initializer }) /** * DEFINE_RAW_FLEX() - Define an on-stack instance of structure with a trailing * flexible array member, when it does not have a __counted_by annotation. * * @type: structure type name, including "struct" keyword. * @name: Name for a variable to define. * @member: Name of the array member. * @count: Number of elements in the array; must be compile-time const. * * Define a zeroed, on-stack, instance of @type structure with a trailing * flexible array member. * Use __struct_size(@name) to get compile-time size of it afterwards. * Use __member_size(@name->member) to get compile-time size of @name members. * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time number of * elements in array @member. */ #define DEFINE_RAW_FLEX(type, name, member, count) \ __DEFINE_FLEX(type, name, member, count, = { }) /** * DEFINE_FLEX() - Define an on-stack instance of structure with a trailing * flexible array member. * * @TYPE: structure type name, including "struct" keyword. * @NAME: Name for a variable to define. * @MEMBER: Name of the array member. * @COUNTER: Name of the __counted_by member. * @COUNT: Number of elements in the array; must be compile-time const. * * Define a zeroed, on-stack, instance of @TYPE structure with a trailing * flexible array member. * Use __struct_size(@NAME) to get compile-time size of it afterwards. * Use __member_size(@NAME->member) to get compile-time size of @NAME members. * Use STACK_FLEX_ARRAY_SIZE(@name, @member) to get compile-time number of * elements in array @member. */ #define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT) \ _DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .COUNTER = COUNT, }) /** * STACK_FLEX_ARRAY_SIZE() - helper macro for DEFINE_FLEX() family. * Returns the number of elements in @array. * * @name: Name for a variable defined in DEFINE_RAW_FLEX()/DEFINE_FLEX(). * @array: Name of the array member. */ #define STACK_FLEX_ARRAY_SIZE(name, array) \ (__member_size((name)->array) / sizeof(*(name)->array) + \ __must_be_array((name)->array)) /** * typeof_flex_counter() - Return the type of the counter variable of a given * flexible array member annotated by __counted_by(). * @FAM: Instance of flexible array member within a given struct. * * Returns: "size_t" if no annotation exists. */ #define typeof_flex_counter(FAM) \ typeof(_Generic(__flex_counter(FAM), \ void *: (size_t)0, \ default: *__flex_counter(FAM))) /** * overflows_flex_counter_type() - Check if the counter associated with the * given flexible array member can represent * a value. * @TYPE: Type of the struct that contains the @FAM. * @FAM: Member name of the FAM within @TYPE. * @COUNT: Value to check against the __counted_by annotated @FAM's counter. * * Returns: true if @COUNT can be represented in the @FAM's counter. When * @FAM is not annotated with __counted_by(), always returns true. */ #define overflows_flex_counter_type(TYPE, FAM, COUNT) \ (overflows_type(COUNT, typeof_flex_counter(((TYPE *)NULL)->FAM))) /** * __set_flex_counter() - Set the counter associated with the given flexible * array member that has been annoated by __counted_by(). * @FAM: Instance of flexible array member within a given struct. * @COUNT: Value to store to the __counted_by annotated @FAM_PTR's counter. * * This is a no-op if no annotation exists. Count needs to be checked with * overflows_flex_counter_type() before using this function. */ #define __set_flex_counter(FAM, COUNT) \ ({ \ *_Generic(__flex_counter(FAM), \ void *: &(size_t){ 0 }, \ default: __flex_counter(FAM)) = (COUNT); \ }) #endif /* __LINUX_OVERFLOW_H */
