btrfs-progs: kernel-lib: sync include/overflow.h
Sync current version with improved checks. Signed-off-by: David Sterba <dsterba@suse.com>
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David Sterba
parent
e49441a953
commit
5ad2aacd24
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@ -2,8 +2,12 @@
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#ifndef __LINUX_OVERFLOW_H
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#define __LINUX_OVERFLOW_H
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#include <stdbool.h>
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/*
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* It would seem more obvious to do something like
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* We need to compute the minimum and maximum values representable in a given
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* type. These macros may also be useful elsewhere. It would seem more obvious
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* 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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@ -36,128 +40,57 @@
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#define is_non_negative(a) ((a) > 0 || (a) == 0)
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#define is_negative(a) (!(is_non_negative(a)))
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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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/* Copied from linux.git/include/compiler_attributes.h */
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/*
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* gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-warn_005funused_005fresult-function-attribute
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* clang: https://clang.llvm.org/docs/AttributeReference.html#nodiscard-warn-unused-result
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*/
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#define __must_check __attribute__((__warn_unused_result__))
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/*
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* Allows for effectively applying __must_check to a macro so we can have
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* both the type-agnostic benefits of the macros while also being able to
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* enforce that the return value is, in fact, checked.
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*/
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static inline bool __must_check __must_check_overflow(bool overflow)
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{
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return overflow;
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}
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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) __must_check_overflow(({ \
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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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__builtin_add_overflow(__a, __b, __d); \
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}))
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#define check_sub_overflow(a, b, d) __must_check_overflow(({ \
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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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__builtin_sub_overflow(__a, __b, __d); \
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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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* 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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#define check_mul_overflow(a, b, d) __must_check_overflow(({ \
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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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* 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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* 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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#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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#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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#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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#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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__builtin_mul_overflow(__a, __b, __d); \
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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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@ -176,9 +109,9 @@
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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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* considered "safe for use" if true is returned.
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*/
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#define check_shl_overflow(a, s, d) ({ \
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#define check_shl_overflow(a, s, d) __must_check_overflow(({ \
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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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@ -188,7 +121,70 @@
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*_d = (_a_full << _to_shift); \
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(_to_shift != _s || is_negative(*_d) || is_negative(_a) || \
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(*_d >> _to_shift) != _a); \
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})
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}))
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/**
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* size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX
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*
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* @factor1: first factor
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* @factor2: second factor
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*
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* Returns: calculate @factor1 * @factor2, both promoted to size_t,
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* with any overflow causing the return value to be SIZE_MAX. The
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* lvalue must be size_t to avoid implicit type conversion.
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*/
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static inline size_t __must_check size_mul(size_t factor1, size_t factor2)
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{
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size_t bytes;
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if (check_mul_overflow(factor1, factor2, &bytes))
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return SIZE_MAX;
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return bytes;
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}
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/**
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* size_add() - Calculate size_t addition with saturation at SIZE_MAX
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*
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* @addend1: first addend
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* @addend2: second addend
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*
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* Returns: calculate @addend1 + @addend2, both promoted to size_t,
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* with any overflow causing the return value to be SIZE_MAX. The
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* lvalue must be size_t to avoid implicit type conversion.
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*/
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static inline size_t __must_check size_add(size_t addend1, size_t addend2)
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{
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size_t bytes;
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if (check_add_overflow(addend1, addend2, &bytes))
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return SIZE_MAX;
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return bytes;
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}
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/**
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* size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX
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*
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* @minuend: value to subtract from
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* @subtrahend: value to subtract from @minuend
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*
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* Returns: calculate @minuend - @subtrahend, both promoted to size_t,
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* with any overflow causing the return value to be SIZE_MAX. For
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* composition with the size_add() and size_mul() helpers, neither
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* argument may be SIZE_MAX (or the result with be forced to SIZE_MAX).
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* The lvalue must be size_t to avoid implicit type conversion.
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*/
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static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
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{
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size_t bytes;
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if (minuend == SIZE_MAX || subtrahend == SIZE_MAX ||
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check_sub_overflow(minuend, subtrahend, &bytes))
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return SIZE_MAX;
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return bytes;
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}
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/**
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* array_size() - Calculate size of 2-dimensional array.
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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 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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if (check_mul_overflow(a, b, &bytes))
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return SIZE_MAX;
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return bytes;
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}
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#define array_size(a, b) size_mul(a, b)
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/**
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* array3_size() - Calculate size of 3-dimensional array.
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@ -223,48 +211,41 @@ static inline size_t array_size(size_t a, size_t b)
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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 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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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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return bytes;
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}
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/*
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* Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
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* struct_size() below.
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*/
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static inline size_t __ab_c_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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if (check_mul_overflow(a, b, &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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return bytes;
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}
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#define array3_size(a, b, c) size_mul(size_mul(a, b), c)
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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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* flex_array_size() - Calculate size of a flexible array member
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* within an enclosing structure.
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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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* @p: Pointer to the structure.
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* @member: Name of the flexible array member.
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* @count: Number of elements in the array.
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*
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* Calculates size of a flexible array of @count number of @member
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* elements, at the end of structure @p.
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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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#define flex_array_size(p, member, count) \
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__builtin_choose_expr(__is_constexpr(count), \
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(count) * sizeof(*(p)->member) + __must_be_array((p)->member), \
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size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member)))
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/**
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* struct_size() - Calculate size of structure with trailing flexible array.
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*
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* @p: Pointer to the structure.
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* @member: Name of the array member.
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* @count: 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 @count number of @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, count) \
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__builtin_choose_expr(__is_constexpr(count), \
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sizeof(*(p)) + flex_array_size(p, member, count), \
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size_add(sizeof(*(p)), flex_array_size(p, member, count)))
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#endif /* __LINUX_OVERFLOW_H */
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