LinuxKPI: Import vanilla linux/overflow.h

It is dual-licensed (GPLv2 & MIT) and self-contained header file.
No need to reimplement it.

Sponsored by:	Serenity CyberSecurity, LLC
Reviewed by:	emaste
MFC after:	1 week

7 files changed, 352 insertions, 76 deletions

diff --git a/sys/compat/linuxkpi/common/include/linux/compiler.h b/sys/compat/linuxkpi/common/include/linux/compiler.h
index 97687ccdc7e1..1ae41d9ba641 100644
--- a/sys/compat/linuxkpi/common/include/linux/compiler.h
+++ b/sys/compat/linuxkpi/common/include/linux/compiler.h
@@ -110,4 +110,7 @@
 
 #define	sizeof_field(_s, _m)	sizeof(((_s *)0)->_m)
 
+#define is_signed_type(t)	((t)-1 < (t)1)
+#define is_unsigned_type(t)	((t)-1 > (t)1)
+
 #endif	/* _LINUXKPI_LINUX_COMPILER_H_ */
diff --git a/sys/compat/linuxkpi/common/include/linux/device.h b/sys/compat/linuxkpi/common/include/linux/device.h
index b4cd97931672..77c7a253a2e8 100644
--- a/sys/compat/linuxkpi/common/include/linux/device.h
+++ b/sys/compat/linuxkpi/common/include/linux/device.h
@@ -45,6 +45,7 @@
 #include <linux/backlight.h>
 #include <linux/pm.h>
 #include <linux/idr.h>
+#include <linux/overflow.h>
 #include <linux/ratelimit.h>	/* via linux/dev_printk.h */
 #include <linux/fwnode.h>
 #include <asm/atomic.h>
diff --git a/sys/compat/linuxkpi/common/include/linux/kernel.h b/sys/compat/linuxkpi/common/include/linux/kernel.h
index 96259716d3a7..16499ef96a50 100644
--- a/sys/compat/linuxkpi/common/include/linux/kernel.h
+++ b/sys/compat/linuxkpi/common/include/linux/kernel.h
@@ -593,12 +593,6 @@ linux_ratelimited(linux_ratelimit_t *rl)
 	return (ppsratecheck(&rl->lasttime, &rl->counter, 1));
 }
 
-#define	struct_size(ptr, field, num) ({ \
-	const size_t __size = offsetof(__typeof(*(ptr)), field); \
-	const size_t __max = (SIZE_MAX - __size) / sizeof((ptr)->field[0]); \
-	((num) > __max) ? SIZE_MAX : (__size + sizeof((ptr)->field[0]) * (num)); \
-})
-
 #define	__is_constexpr(x) \
 	__builtin_constant_p(x)
 
@@ -608,29 +602,6 @@ linux_ratelimited(linux_ratelimit_t *rl)
  */
 #define	is_signed(datatype) (((datatype)-1 / (datatype)2) == (datatype)0)
 
-/*
- * The type_max() macro below returns the maxium positive value the
- * passed data type can hold.
- */
-#define	type_max(datatype) ( \
-  (sizeof(datatype) >= 8) ? (is_signed(datatype) ? INT64_MAX : UINT64_MAX) : \
-  (sizeof(datatype) >= 4) ? (is_signed(datatype) ? INT32_MAX : UINT32_MAX) : \
-  (sizeof(datatype) >= 2) ? (is_signed(datatype) ? INT16_MAX : UINT16_MAX) : \
-			    (is_signed(datatype) ? INT8_MAX : UINT8_MAX) \
-)
-
-/*
- * The type_min() macro below returns the minimum value the passed
- * data type can hold. For unsigned types the minimum value is always
- * zero. For signed types it may vary.
- */
-#define	type_min(datatype) ( \
-  (sizeof(datatype) >= 8) ? (is_signed(datatype) ? INT64_MIN : 0) : \
-  (sizeof(datatype) >= 4) ? (is_signed(datatype) ? INT32_MIN : 0) : \
-  (sizeof(datatype) >= 2) ? (is_signed(datatype) ? INT16_MIN : 0) : \
-			    (is_signed(datatype) ? INT8_MIN : 0) \
-)
-
 #define	TAINT_WARN	0
 #define	test_taint(x)	(0)
 #define	add_taint(x,y)	do {	\
diff --git a/sys/compat/linuxkpi/common/include/linux/mm.h b/sys/compat/linuxkpi/common/include/linux/mm.h
index 8c50a2bbb3bc..1356d64dde28 100644
--- a/sys/compat/linuxkpi/common/include/linux/mm.h
+++ b/sys/compat/linuxkpi/common/include/linux/mm.h
@@ -38,6 +38,7 @@
 #include <linux/pfn.h>
 #include <linux/list.h>
 #include <linux/mmap_lock.h>
+#include <linux/overflow.h>
 #include <linux/shrinker.h>
 #include <linux/page.h>
 
diff --git a/sys/compat/linuxkpi/common/include/linux/overflow.h b/sys/compat/linuxkpi/common/include/linux/overflow.h
index bb9ac5bc5ffd..9ba9b9500f11 100644
--- a/sys/compat/linuxkpi/common/include/linux/overflow.h
+++ b/sys/compat/linuxkpi/common/include/linux/overflow.h
@@ -1,51 +1,349 @@
-/*-
- * Copyright (c) 2020 The FreeBSD Foundation
- *
- * This software was developed by Emmanuel Vadot under sponsorship
- * from the FreeBSD Foundation.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
-
-#ifndef __LINUXKPI_LINUX_OVERFLOW_H__
-#define	__LINUXKPI_LINUX_OVERFLOW_H__
-
-#include <sys/stdint.h>
-#include <sys/types.h>
-
-#define check_add_overflow(a, b, c)		\
-	__builtin_add_overflow(a, b, c)
-
-#define check_mul_overflow(a, b, c)	\
-	__builtin_mul_overflow(a, b, c)
-
-static inline size_t
-array_size(size_t x, size_t y)
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+#ifndef _LINUXKPI_LINUX_OVERFLOW_H
+#define _LINUXKPI_LINUX_OVERFLOW_H
+
+#include <linux/compiler.h>
+#include <linux/limits.h>
+#ifdef __linux__
+#include <linux/const.h>
+#endif
+
+/*
+ * 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_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)
 {
-	size_t retval;
+	return unlikely(overflow);
+}
+
+/**
+ * check_add_overflow() - Calculate addition with overflow checking
+ * @a: first addend
+ * @b: second addend
+ * @d: pointer to store sum
+ *
+ * Returns 0 on success.
+ *
+ * *@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))
+
+/**
+ * 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
+ * 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);					\
+}))
+
+#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);		\
+})
+
+/**
+ * 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))
 
-	if (__builtin_mul_overflow(x, y, &retval))
-		retval = SIZE_MAX;
-	return (retval);
+/**
+ * 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;
 }
 
-#endif	/* __LINUXKPI_LINUX_OVERFLOW_H__ */
+/**
+ * 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_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.
+ * @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, count)			\
+	_DEFINE_FLEX(type, name, member, count, = {})
+
+#endif /* _LINUXKPI_LINUX_OVERFLOW_H */
diff --git a/sys/compat/linuxkpi/common/include/linux/string.h b/sys/compat/linuxkpi/common/include/linux/string.h
index 13c8fee602dd..1365b7d7823a 100644
--- a/sys/compat/linuxkpi/common/include/linux/string.h
+++ b/sys/compat/linuxkpi/common/include/linux/string.h
@@ -37,6 +37,7 @@
 #include <linux/uaccess.h>
 #include <linux/err.h>
 #include <linux/bitops.h> /* for BITS_PER_LONG */
+#include <linux/overflow.h>
 #include <linux/stdarg.h>
 
 #include <sys/libkern.h>
diff --git a/sys/compat/linuxkpi/common/include/linux/vmalloc.h b/sys/compat/linuxkpi/common/include/linux/vmalloc.h
index 0a5cf0d409bf..00650a2df9b6 100644
--- a/sys/compat/linuxkpi/common/include/linux/vmalloc.h
+++ b/sys/compat/linuxkpi/common/include/linux/vmalloc.h
@@ -29,6 +29,7 @@
 #ifndef _LINUXKPI_LINUX_VMALLOC_H_
 #define	_LINUXKPI_LINUX_VMALLOC_H_
 
+#include <linux/overflow.h>
 #include <linux/page.h>
 
 #define	VM_MAP		0x0000