cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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overflow.h (4207B)

      1/* SPDX-License-Identifier: GPL-2.0 OR MIT */
      2#ifndef __LINUX_OVERFLOW_H
      3#define __LINUX_OVERFLOW_H
      4
      5#include <linux/compiler.h>
      6
      7/*
      8 * We need to compute the minimum and maximum values representable in a given
      9 * type. These macros may also be useful elsewhere. It would seem more obvious
     10 * to do something like:
     11 *
     12 * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
     13 * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
     14 *
     15 * Unfortunately, the middle expressions, strictly speaking, have
     16 * undefined behaviour, and at least some versions of gcc warn about
     17 * the type_max expression (but not if -fsanitize=undefined is in
     18 * effect; in that case, the warning is deferred to runtime...).
     19 *
     20 * The slightly excessive casting in type_min is to make sure the
     21 * macros also produce sensible values for the exotic type _Bool. [The
     22 * overflow checkers only almost work for _Bool, but that's
     23 * a-feature-not-a-bug, since people shouldn't be doing arithmetic on
     24 * _Bools. Besides, the gcc builtins don't allow _Bool* as third
     25 * argument.]
     26 *
     27 * Idea stolen from
     28 * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -
     29 * credit to Christian Biere.
     30 */
     31#define is_signed_type(type)       (((type)(-1)) < (type)1)
     32#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
     33#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
     34#define type_min(T) ((T)((T)-type_max(T)-(T)1))
     35
     36/*
     37 * For simplicity and code hygiene, the fallback code below insists on
     38 * a, b and *d having the same type (similar to the min() and max()
     39 * macros), whereas gcc's type-generic overflow checkers accept
     40 * different types. Hence we don't just make check_add_overflow an
     41 * alias for __builtin_add_overflow, but add type checks similar to
     42 * below.
     43 */
     44#define check_add_overflow(a, b, d) ({		\
     45	typeof(a) __a = (a);			\
     46	typeof(b) __b = (b);			\
     47	typeof(d) __d = (d);			\
     48	(void) (&__a == &__b);			\
     49	(void) (&__a == __d);			\
     50	__builtin_add_overflow(__a, __b, __d);	\
     51})
     52
     53#define check_sub_overflow(a, b, d) ({		\
     54	typeof(a) __a = (a);			\
     55	typeof(b) __b = (b);			\
     56	typeof(d) __d = (d);			\
     57	(void) (&__a == &__b);			\
     58	(void) (&__a == __d);			\
     59	__builtin_sub_overflow(__a, __b, __d);	\
     60})
     61
     62#define check_mul_overflow(a, b, d) ({		\
     63	typeof(a) __a = (a);			\
     64	typeof(b) __b = (b);			\
     65	typeof(d) __d = (d);			\
     66	(void) (&__a == &__b);			\
     67	(void) (&__a == __d);			\
     68	__builtin_mul_overflow(__a, __b, __d);	\
     69})
     70
     71/**
     72 * array_size() - Calculate size of 2-dimensional array.
     73 *
     74 * @a: dimension one
     75 * @b: dimension two
     76 *
     77 * Calculates size of 2-dimensional array: @a * @b.
     78 *
     79 * Returns: number of bytes needed to represent the array or SIZE_MAX on
     80 * overflow.
     81 */
     82static inline __must_check size_t array_size(size_t a, size_t b)
     83{
     84	size_t bytes;
     85
     86	if (check_mul_overflow(a, b, &bytes))
     87		return SIZE_MAX;
     88
     89	return bytes;
     90}
     91
     92/**
     93 * array3_size() - Calculate size of 3-dimensional array.
     94 *
     95 * @a: dimension one
     96 * @b: dimension two
     97 * @c: dimension three
     98 *
     99 * Calculates size of 3-dimensional array: @a * @b * @c.
    100 *
    101 * Returns: number of bytes needed to represent the array or SIZE_MAX on
    102 * overflow.
    103 */
    104static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)
    105{
    106	size_t bytes;
    107
    108	if (check_mul_overflow(a, b, &bytes))
    109		return SIZE_MAX;
    110	if (check_mul_overflow(bytes, c, &bytes))
    111		return SIZE_MAX;
    112
    113	return bytes;
    114}
    115
    116static inline __must_check size_t __ab_c_size(size_t n, size_t size, size_t c)
    117{
    118	size_t bytes;
    119
    120	if (check_mul_overflow(n, size, &bytes))
    121		return SIZE_MAX;
    122	if (check_add_overflow(bytes, c, &bytes))
    123		return SIZE_MAX;
    124
    125	return bytes;
    126}
    127
    128/**
    129 * struct_size() - Calculate size of structure with trailing array.
    130 * @p: Pointer to the structure.
    131 * @member: Name of the array member.
    132 * @n: Number of elements in the array.
    133 *
    134 * Calculates size of memory needed for structure @p followed by an
    135 * array of @n @member elements.
    136 *
    137 * Return: number of bytes needed or SIZE_MAX on overflow.
    138 */
    139#define struct_size(p, member, n)					\
    140	__ab_c_size(n,							\
    141		    sizeof(*(p)->member) + __must_be_array((p)->member),\
    142		    sizeof(*(p)))
    143
    144#endif /* __LINUX_OVERFLOW_H */