@@ -3,6 +3,8 @@
#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
@@ -28,117 +30,318 @@
* 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))
/*
- * 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.
- */
-#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); \
-})
+ * 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)))
-#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); \
-})
+/*
+ * 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 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 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); \
+#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
*
- * @a: dimension one
- * @b: dimension two
+ * @n: source constant value or variable to be checked
+ * @T: destination variable or data type proposed to store @x
*
- * Calculates size of 2-dimensional array: @a * @b.
+ * 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: number of bytes needed to represent the array or SIZE_MAX on
- * overflow.
+ * 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().
*/
-static inline __must_check size_t array_size(size_t a, size_t b)
+#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(a, b, &bytes))
+ if (check_mul_overflow(factor1, factor2, &bytes))
return SIZE_MAX;
return bytes;
}
/**
- * array3_size() - Calculate size of 3-dimensional array.
+ * size_add() - Calculate size_t addition with saturation at SIZE_MAX
+ * @addend1: first addend
+ * @addend2: second addend
*
- * @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.
+ * 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 __must_check size_t array3_size(size_t a, size_t b, size_t c)
+static inline size_t __must_check size_add(size_t addend1, size_t addend2)
{
size_t bytes;
- if (check_mul_overflow(a, b, &bytes))
- return SIZE_MAX;
- if (check_mul_overflow(bytes, c, &bytes))
+ if (check_add_overflow(addend1, addend2, &bytes))
return SIZE_MAX;
return bytes;
}
-static inline __must_check size_t __ab_c_size(size_t n, size_t size, size_t c)
+/**
+ * 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 (check_mul_overflow(n, size, &bytes))
- return SIZE_MAX;
- if (check_add_overflow(bytes, c, &bytes))
+ if (minuend == SIZE_MAX || subtrahend == SIZE_MAX ||
+ check_sub_overflow(minuend, subtrahend, &bytes))
return SIZE_MAX;
return bytes;
}
/**
- * struct_size() - Calculate size of structure with trailing array.
+ * 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.
- * @n: Number of elements in the array.
+ * @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 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(p, member, n) \
- __ab_c_size(n, \
- sizeof(*(p)->member) + __must_be_array((p)->member),\
- sizeof(*(p)))
+#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 /* __LINUX_OVERFLOW_H */
@@ -35,6 +35,7 @@ FILES=(
"include/vdso/const.h"
"include/linux/hash.h"
"include/linux/list-sort.h"
+ "include/linux/overflow.h"
"include/uapi/linux/hw_breakpoint.h"
"arch/x86/include/asm/disabled-features.h"
"arch/x86/include/asm/required-features.h"
Bring in the changes: 26dd68d293fd overflow: add DEFINE_FLEX() for on-stack allocs d67790ddf021 overflow: Add struct_size_t() helper 4b21d25bf519 overflow: Introduce overflows_type() and castable_to_type() 31970608a6d3 overflow: Fix kern-doc markup for functions d219d2a9a92e overflow: Allow mixed type arguments 92d23c6e9415 overflow, tracing: Define the is_signed_type() macro once 230f6fa2c1db overflow: Provide constant expression struct_size e1be43d9b5d0 overflow: Implement size_t saturating arithmetic helpers Add file to check-headers.sh, so there is a warning if the tools version of the file drifts from the kernel's version. Signed-off-by: Ian Rogers <irogers@google.com> --- tools/include/linux/overflow.h | 331 ++++++++++++++++++++++++++------- tools/perf/check-headers.sh | 1 + 2 files changed, 268 insertions(+), 64 deletions(-)