323 lines
9.9 KiB
Diff
323 lines
9.9 KiB
Diff
--- a/backport-include/linux/slab.h
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+++ b/backport-include/linux/slab.h
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@@ -1,6 +1,7 @@
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#ifndef __BACKPORT_SLAB_H
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#define __BACKPORT_SLAB_H
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#include_next <linux/slab.h>
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+#include <linux/overflow.h>
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#include <linux/version.h>
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#if LINUX_VERSION_IS_LESS(3,4,0)
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--- /dev/null
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+++ b/include/linux/overflow.h
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@@ -0,0 +1,309 @@
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+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
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+#ifndef __LINUX_OVERFLOW_H
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+#define __LINUX_OVERFLOW_H
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+
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+#include <linux/compiler.h>
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+
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+/*
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+ * In the fallback code below, we need to compute the minimum and
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+ * maximum values representable in a given type. These macros may also
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+ * be useful elsewhere, so we provide them outside the
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+ * COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
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+ *
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+ * It would seem more obvious to do something like
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+ *
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+ * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
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+ * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
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+ *
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+ * Unfortunately, the middle expressions, strictly speaking, have
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+ * undefined behaviour, and at least some versions of gcc warn about
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+ * the type_max expression (but not if -fsanitize=undefined is in
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+ * effect; in that case, the warning is deferred to runtime...).
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+ *
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+ * The slightly excessive casting in type_min is to make sure the
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+ * macros also produce sensible values for the exotic type _Bool. [The
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+ * overflow checkers only almost work for _Bool, but that's
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+ * a-feature-not-a-bug, since people shouldn't be doing arithmetic on
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+ * _Bools. Besides, the gcc builtins don't allow _Bool* as third
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+ * argument.]
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+ *
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+ * Idea stolen from
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+ * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -
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+ * credit to Christian Biere.
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+ */
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+#define is_signed_type(type) (((type)(-1)) < (type)1)
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+#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
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+#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
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+#define type_min(T) ((T)((T)-type_max(T)-(T)1))
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+
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+
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+#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
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+/*
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+ * For simplicity and code hygiene, the fallback code below insists on
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+ * a, b and *d having the same type (similar to the min() and max()
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+ * macros), whereas gcc's type-generic overflow checkers accept
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+ * different types. Hence we don't just make check_add_overflow an
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+ * alias for __builtin_add_overflow, but add type checks similar to
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+ * below.
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+ */
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+#define check_add_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ __builtin_add_overflow(__a, __b, __d); \
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+})
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+
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+#define check_sub_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ __builtin_sub_overflow(__a, __b, __d); \
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+})
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+
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+#define check_mul_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ __builtin_mul_overflow(__a, __b, __d); \
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+})
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+
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+#else
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+
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+
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+/* Checking for unsigned overflow is relatively easy without causing UB. */
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+#define __unsigned_add_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ *__d = __a + __b; \
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+ *__d < __a; \
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+})
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+#define __unsigned_sub_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ *__d = __a - __b; \
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+ __a < __b; \
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+})
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+/*
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+ * If one of a or b is a compile-time constant, this avoids a division.
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+ */
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+#define __unsigned_mul_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ *__d = __a * __b; \
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+ __builtin_constant_p(__b) ? \
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+ __b > 0 && __a > type_max(typeof(__a)) / __b : \
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+ __a > 0 && __b > type_max(typeof(__b)) / __a; \
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+})
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+
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+/*
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+ * For signed types, detecting overflow is much harder, especially if
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+ * we want to avoid UB. But the interface of these macros is such that
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+ * we must provide a result in *d, and in fact we must produce the
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+ * result promised by gcc's builtins, which is simply the possibly
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+ * wrapped-around value. Fortunately, we can just formally do the
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+ * operations in the widest relevant unsigned type (u64) and then
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+ * truncate the result - gcc is smart enough to generate the same code
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+ * with and without the (u64) casts.
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+ */
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+
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+/*
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+ * Adding two signed integers can overflow only if they have the same
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+ * sign, and overflow has happened iff the result has the opposite
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+ * sign.
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+ */
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+#define __signed_add_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ *__d = (u64)__a + (u64)__b; \
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+ (((~(__a ^ __b)) & (*__d ^ __a)) \
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+ & type_min(typeof(__a))) != 0; \
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+})
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+
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+/*
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+ * Subtraction is similar, except that overflow can now happen only
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+ * when the signs are opposite. In this case, overflow has happened if
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+ * the result has the opposite sign of a.
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+ */
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+#define __signed_sub_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ *__d = (u64)__a - (u64)__b; \
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+ ((((__a ^ __b)) & (*__d ^ __a)) \
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+ & type_min(typeof(__a))) != 0; \
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+})
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+
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+/*
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+ * Signed multiplication is rather hard. gcc always follows C99, so
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+ * division is truncated towards 0. This means that we can write the
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+ * overflow check like this:
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+ *
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+ * (a > 0 && (b > MAX/a || b < MIN/a)) ||
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+ * (a < -1 && (b > MIN/a || b < MAX/a) ||
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+ * (a == -1 && b == MIN)
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+ *
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+ * The redundant casts of -1 are to silence an annoying -Wtype-limits
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+ * (included in -Wextra) warning: When the type is u8 or u16, the
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+ * __b_c_e in check_mul_overflow obviously selects
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+ * __unsigned_mul_overflow, but unfortunately gcc still parses this
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+ * code and warns about the limited range of __b.
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+ */
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+
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+#define __signed_mul_overflow(a, b, d) ({ \
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+ typeof(a) __a = (a); \
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+ typeof(b) __b = (b); \
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+ typeof(d) __d = (d); \
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+ typeof(a) __tmax = type_max(typeof(a)); \
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+ typeof(a) __tmin = type_min(typeof(a)); \
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+ (void) (&__a == &__b); \
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+ (void) (&__a == __d); \
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+ *__d = (u64)__a * (u64)__b; \
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+ (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
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+ (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
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+ (__b == (typeof(__b))-1 && __a == __tmin); \
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+})
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+
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+
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+#define check_add_overflow(a, b, d) \
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+ __builtin_choose_expr(is_signed_type(typeof(a)), \
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+ __signed_add_overflow(a, b, d), \
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+ __unsigned_add_overflow(a, b, d))
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+
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+#define check_sub_overflow(a, b, d) \
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+ __builtin_choose_expr(is_signed_type(typeof(a)), \
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+ __signed_sub_overflow(a, b, d), \
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+ __unsigned_sub_overflow(a, b, d))
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+
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+#define check_mul_overflow(a, b, d) \
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+ __builtin_choose_expr(is_signed_type(typeof(a)), \
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+ __signed_mul_overflow(a, b, d), \
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+ __unsigned_mul_overflow(a, b, d))
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+
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+
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+#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
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+
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+/** check_shl_overflow() - Calculate a left-shifted value and check overflow
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+ *
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+ * @a: Value to be shifted
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+ * @s: How many bits left to shift
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+ * @d: Pointer to where to store the result
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+ *
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+ * Computes *@d = (@a << @s)
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+ *
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+ * Returns true if '*d' cannot hold the result or when 'a << s' doesn't
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+ * make sense. Example conditions:
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+ * - 'a << s' causes bits to be lost when stored in *d.
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+ * - 's' is garbage (e.g. negative) or so large that the result of
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+ * 'a << s' is guaranteed to be 0.
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+ * - 'a' is negative.
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+ * - 'a << s' sets the sign bit, if any, in '*d'.
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+ *
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+ * '*d' will hold the results of the attempted shift, but is not
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+ * considered "safe for use" if false is returned.
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+ */
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+#define check_shl_overflow(a, s, d) ({ \
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+ typeof(a) _a = a; \
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+ typeof(s) _s = s; \
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+ typeof(d) _d = d; \
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+ u64 _a_full = _a; \
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+ unsigned int _to_shift = \
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+ _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
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+ *_d = (_a_full << _to_shift); \
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+ (_to_shift != _s || *_d < 0 || _a < 0 || \
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+ (*_d >> _to_shift) != _a); \
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+})
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+
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+/**
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+ * array_size() - Calculate size of 2-dimensional array.
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+ *
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+ * @a: dimension one
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+ * @b: dimension two
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+ *
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+ * Calculates size of 2-dimensional array: @a * @b.
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+ *
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+ * Returns: number of bytes needed to represent the array or SIZE_MAX on
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+ * overflow.
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+ */
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+static inline __must_check size_t array_size(size_t a, size_t b)
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+{
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+ size_t bytes;
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+
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+ if (check_mul_overflow(a, b, &bytes))
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+ return SIZE_MAX;
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+
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+ return bytes;
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+}
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+
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+/**
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+ * array3_size() - Calculate size of 3-dimensional array.
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+ *
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+ * @a: dimension one
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+ * @b: dimension two
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+ * @c: dimension three
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+ *
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+ * Calculates size of 3-dimensional array: @a * @b * @c.
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+ *
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+ * Returns: number of bytes needed to represent the array or SIZE_MAX on
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+ * overflow.
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+ */
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+static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)
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+{
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+ size_t bytes;
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+
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+ if (check_mul_overflow(a, b, &bytes))
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+ return SIZE_MAX;
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+ if (check_mul_overflow(bytes, c, &bytes))
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+ return SIZE_MAX;
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+
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+ return bytes;
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+}
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+
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+static inline __must_check size_t __ab_c_size(size_t n, size_t size, size_t c)
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+{
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+ size_t bytes;
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+
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+ if (check_mul_overflow(n, size, &bytes))
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+ return SIZE_MAX;
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+ if (check_add_overflow(bytes, c, &bytes))
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+ return SIZE_MAX;
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+
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+ return bytes;
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+}
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+
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+/**
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+ * struct_size() - Calculate size of structure with trailing array.
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+ * @p: Pointer to the structure.
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+ * @member: Name of the array member.
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+ * @n: Number of elements in the array.
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+ *
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+ * Calculates size of memory needed for structure @p followed by an
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+ * array of @n @member elements.
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+ *
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+ * Return: number of bytes needed or SIZE_MAX on overflow.
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+ */
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+#define struct_size(p, member, n) \
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+ __ab_c_size(n, \
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+ sizeof(*(p)->member) + __must_be_array((p)->member),\
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+ sizeof(*(p)))
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+
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+#endif /* __LINUX_OVERFLOW_H */
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