From: Simon Glass <simon.gl...@canonical.com> Add this file from Linux v6.14 so we can use it to add overflow checks, rather than using compiler built-ins directly.
Signed-off-by: Simon Glass <simon.gl...@canonical.com> Suggested-by: Tom Rini <tr...@konsulko.com> --- Changes in v2: - Add new patch to bring in linux/overflow.h include/linux/overflow.h | 443 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 443 insertions(+) create mode 100644 include/linux/overflow.h diff --git a/include/linux/overflow.h b/include/linux/overflow.h new file mode 100644 index 00000000000..0c7e3dcfe86 --- /dev/null +++ b/include/linux/overflow.h @@ -0,0 +1,443 @@ +/* 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)) + +/* + * 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); +} + +/** + * 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 = \ + 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); \ +})) + +#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)) + +/** + * 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 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 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 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) + +/** + * _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 (could be empty for no init). + */ +#define _DEFINE_FLEX(type, name, member, count, initializer...) \ + _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 initializer; \ + type *name = (type *)&name##_u + +/** + * 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. + */ +#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. + */ +#define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT) \ + _DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, }) + +#endif /* __LINUX_OVERFLOW_H */ -- 2.43.0 base-commit: 5841e78ed6ebd31b26553003e880be378b232cd9 branch: sec2
