[PATCH v2 2/3] Bring in linux/overflow.h
Simon Glass
sjg at chromium.org
Fri Apr 18 12:59:14 CEST 2025
From: Simon Glass <simon.glass at 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.glass at canonical.com>
Suggested-by: Tom Rini <trini at 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
More information about the U-Boot
mailing list