On Fri, Oct 20, 2023 at 09:23:14AM +0200, Ahmad Fatoum wrote: > Newer versions of the header add a size_add macro for doing saturating > addition, which will be used in a follow-up fix, so sync the header with > Linux to make it available. > > Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx> > --- > include/linux/overflow.h | 436 +++++++++++++++++++-------------------- > 1 file changed, 214 insertions(+), 222 deletions(-) Applied, thanks Sascha > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > index 50c93ca0c3d6..f9b60313eaea 100644 > --- a/include/linux/overflow.h > +++ b/include/linux/overflow.h > @@ -4,14 +4,12 @@ > > #include <linux/compiler.h> > #include <linux/limits.h> > +#include <linux/const.h> > > /* > - * In the fallback code below, we need to compute the minimum and > - * maximum values representable in a given type. These macros may also > - * be useful elsewhere, so we provide them outside the > - * COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block. > - * > - * It would seem more obvious to do something like > + * 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) > @@ -32,7 +30,6 @@ > * 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)) > @@ -44,191 +41,82 @@ > #define is_non_negative(a) ((a) > 0 || (a) == 0) > #define is_negative(a) (!(is_non_negative(a))) > > -#ifdef COMPILER_HAS_GENERIC_BUILTIN_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. > + * 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. > */ > -#define check_add_overflow(a, b, d) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - __builtin_add_overflow(__a, __b, __d); \ > -}) > +static inline bool __must_check __must_check_overflow(bool overflow) > +{ > + return unlikely(overflow); > +} > > -#define check_sub_overflow(a, b, d) ({ \ > - 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) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - __builtin_mul_overflow(__a, __b, __d); \ > -}) > - > -#else > - > - > -/* Checking for unsigned overflow is relatively easy without causing UB. */ > -#define __unsigned_add_overflow(a, b, d) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - *__d = __a + __b; \ > - *__d < __a; \ > -}) > -#define __unsigned_sub_overflow(a, b, d) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - *__d = __a - __b; \ > - __a < __b; \ > -}) > -/* > - * If one of a or b is a compile-time constant, this avoids a division. > - */ > -#define __unsigned_mul_overflow(a, b, d) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - *__d = __a * __b; \ > - __builtin_constant_p(__b) ? \ > - __b > 0 && __a > type_max(typeof(__a)) / __b : \ > - __a > 0 && __b > type_max(typeof(__b)) / __a; \ > -}) > - > -/* > - * For signed types, detecting overflow is much harder, especially if > - * we want to avoid UB. But the interface of these macros is such that > - * we must provide a result in *d, and in fact we must produce the > - * result promised by gcc's builtins, which is simply the possibly > - * wrapped-around value. Fortunately, we can just formally do the > - * operations in the widest relevant unsigned type (u64) and then > - * truncate the result - gcc is smart enough to generate the same code > - * with and without the (u64) casts. > - */ > - > -/* > - * Adding two signed integers can overflow only if they have the same > - * sign, and overflow has happened iff the result has the opposite > - * sign. > - */ > -#define __signed_add_overflow(a, b, d) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - *__d = (u64)__a + (u64)__b; \ > - (((~(__a ^ __b)) & (*__d ^ __a)) \ > - & type_min(typeof(__a))) != 0; \ > -}) > - > -/* > - * Subtraction is similar, except that overflow can now happen only > - * when the signs are opposite. In this case, overflow has happened if > - * the result has the opposite sign of a. > - */ > -#define __signed_sub_overflow(a, b, d) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - *__d = (u64)__a - (u64)__b; \ > - ((((__a ^ __b)) & (*__d ^ __a)) \ > - & type_min(typeof(__a))) != 0; \ > -}) > - > -/* > - * Signed multiplication is rather hard. gcc always follows C99, so > - * division is truncated towards 0. This means that we can write the > - * overflow check like this: > +/** > + * check_add_overflow() - Calculate addition with overflow checking > + * @a: first addend > + * @b: second addend > + * @d: pointer to store sum > * > - * (a > 0 && (b > MAX/a || b < MIN/a)) || > - * (a < -1 && (b > MIN/a || b < MAX/a) || > - * (a == -1 && b == MIN) > + * Returns 0 on success. > * > - * The redundant casts of -1 are to silence an annoying -Wtype-limits > - * (included in -Wextra) warning: When the type is u8 or u16, the > - * __b_c_e in check_mul_overflow obviously selects > - * __unsigned_mul_overflow, but unfortunately gcc still parses this > - * code and warns about the limited range of __b. > + * *@d holds the results of the attempted addition, but is not considered > + * "safe for use" on a non-zero return value, which indicates that the > + * sum has overflowed or been truncated. > */ > +#define check_add_overflow(a, b, d) \ > + __must_check_overflow(__builtin_add_overflow(a, b, d)) > > -#define __signed_mul_overflow(a, b, d) ({ \ > - typeof(a) __a = (a); \ > - typeof(b) __b = (b); \ > - typeof(d) __d = (d); \ > - typeof(a) __tmax = type_max(typeof(a)); \ > - typeof(a) __tmin = type_min(typeof(a)); \ > - (void) (&__a == &__b); \ > - (void) (&__a == __d); \ > - *__d = (u64)__a * (u64)__b; \ > - (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \ > - (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \ > - (__b == (typeof(__b))-1 && __a == __tmin); \ > -}) > - > - > -#define check_add_overflow(a, b, d) \ > - __builtin_choose_expr(is_signed_type(typeof(a)), \ > - __signed_add_overflow(a, b, d), \ > - __unsigned_add_overflow(a, b, d)) > - > -#define check_sub_overflow(a, b, d) \ > - __builtin_choose_expr(is_signed_type(typeof(a)), \ > - __signed_sub_overflow(a, b, d), \ > - __unsigned_sub_overflow(a, b, d)) > - > -#define check_mul_overflow(a, b, d) \ > - __builtin_choose_expr(is_signed_type(typeof(a)), \ > - __signed_mul_overflow(a, b, d), \ > - __unsigned_mul_overflow(a, b, d)) > - > - > -#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */ > - > -/** check_shl_overflow() - Calculate a left-shifted value and check overflow > +/** > + * 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 0 on success. > + * > + * *@d holds the results of the attempted subtraction, but is not considered > + * "safe for use" on a non-zero return value, which indicates that the > + * difference has underflowed or been truncated. > + */ > +#define check_sub_overflow(a, b, d) \ > + __must_check_overflow(__builtin_sub_overflow(a, b, d)) > + > +/** > + * check_mul_overflow() - Calculate multiplication with overflow checking > + * @a: first factor > + * @b: second factor > + * @d: pointer to store product > + * > + * Returns 0 on success. > + * > + * *@d holds the results of the attempted multiplication, but is not > + * considered "safe for use" on a non-zero return value, which indicates > + * that the product has overflowed or been truncated. > + */ > +#define check_mul_overflow(a, b, d) \ > + __must_check_overflow(__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 > + * 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 false is returned. > + * - '@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) ({ \ > +#define check_shl_overflow(a, s, d) __must_check_overflow(({ \ > typeof(a) _a = a; \ > typeof(s) _s = s; \ > typeof(d) _d = d; \ > @@ -238,11 +126,117 @@ > *_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(typeof(T)) : \ > + is_unsigned_type(typeof(T)) ? \ > + (x) < 0 || (x) > type_max(typeof(T)) : \ > + (x) < type_min(typeof(T)) || (x) > type_max(typeof(T))) > + > +#define __overflows_type(x, T) ({ \ > + typeof(T) v = 0; \ > + check_add_overflow((x), v, &v); \ > }) > > /** > - * array_size() - Calculate size of 2-dimensional array. > + * 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 > * > @@ -251,19 +245,10 @@ > * 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; > -} > +#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 > @@ -273,48 +258,55 @@ static inline __must_check size_t array_size(size_t a, size_t b) > * 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; > -} > +#define array3_size(a, b, c) size_mul(size_mul(a, b), c) > > /** > - * struct_size() - Calculate size of structure with trailing array. > + * flex_array_size() - Calculate size of a flexible array member > + * within an enclosing structure. > * @p: Pointer to the structure. > - * @member: Name of the array member. > - * @n: Number of elements in the array. > + * @member: Name of the flexible array member. > + * @count: Number of elements in the array. > * > - * Calculates size of memory needed for structure @p followed by an > - * array of @n @member elements. > + * 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 struct_size(p, member, n) \ > - __ab_c_size(n, \ > - sizeof(*(p)->member) + __must_be_array((p)->member),\ > - sizeof(*(p))) > +#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) > > #endif /* __LINUX_OVERFLOW_H */ > -- > 2.39.2 > > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
