summaryrefslogtreecommitdiffstats
path: root/security/sandbox/chromium/base/numerics/safe_conversions_impl.h
diff options
context:
space:
mode:
Diffstat (limited to 'security/sandbox/chromium/base/numerics/safe_conversions_impl.h')
-rw-r--r--security/sandbox/chromium/base/numerics/safe_conversions_impl.h264
1 files changed, 264 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/numerics/safe_conversions_impl.h b/security/sandbox/chromium/base/numerics/safe_conversions_impl.h
new file mode 100644
index 000000000..02e68e25d
--- /dev/null
+++ b/security/sandbox/chromium/base/numerics/safe_conversions_impl.h
@@ -0,0 +1,264 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
+#define BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_
+
+#include <limits.h>
+#include <stdint.h>
+
+#include <limits>
+
+#include "base/template_util.h"
+
+namespace base {
+namespace internal {
+
+// The std library doesn't provide a binary max_exponent for integers, however
+// we can compute one by adding one to the number of non-sign bits. This allows
+// for accurate range comparisons between floating point and integer types.
+template <typename NumericType>
+struct MaxExponent {
+ static const int value = std::numeric_limits<NumericType>::is_iec559
+ ? std::numeric_limits<NumericType>::max_exponent
+ : (sizeof(NumericType) * 8 + 1 -
+ std::numeric_limits<NumericType>::is_signed);
+};
+
+enum IntegerRepresentation {
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_SIGNED
+};
+
+// A range for a given nunmeric Src type is contained for a given numeric Dst
+// type if both numeric_limits<Src>::max() <= numeric_limits<Dst>::max() and
+// numeric_limits<Src>::min() >= numeric_limits<Dst>::min() are true.
+// We implement this as template specializations rather than simple static
+// comparisons to ensure type correctness in our comparisons.
+enum NumericRangeRepresentation {
+ NUMERIC_RANGE_NOT_CONTAINED,
+ NUMERIC_RANGE_CONTAINED
+};
+
+// Helper templates to statically determine if our destination type can contain
+// maximum and minimum values represented by the source type.
+
+template <
+ typename Dst,
+ typename Src,
+ IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED,
+ IntegerRepresentation SrcSign =
+ std::numeric_limits<Src>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED >
+struct StaticDstRangeRelationToSrcRange;
+
+// Same sign: Dst is guaranteed to contain Src only if its range is equal or
+// larger.
+template <typename Dst, typename Src, IntegerRepresentation Sign>
+struct StaticDstRangeRelationToSrcRange<Dst, Src, Sign, Sign> {
+ static const NumericRangeRepresentation value =
+ MaxExponent<Dst>::value >= MaxExponent<Src>::value
+ ? NUMERIC_RANGE_CONTAINED
+ : NUMERIC_RANGE_NOT_CONTAINED;
+};
+
+// Unsigned to signed: Dst is guaranteed to contain source only if its range is
+// larger.
+template <typename Dst, typename Src>
+struct StaticDstRangeRelationToSrcRange<Dst,
+ Src,
+ INTEGER_REPRESENTATION_SIGNED,
+ INTEGER_REPRESENTATION_UNSIGNED> {
+ static const NumericRangeRepresentation value =
+ MaxExponent<Dst>::value > MaxExponent<Src>::value
+ ? NUMERIC_RANGE_CONTAINED
+ : NUMERIC_RANGE_NOT_CONTAINED;
+};
+
+// Signed to unsigned: Dst cannot be statically determined to contain Src.
+template <typename Dst, typename Src>
+struct StaticDstRangeRelationToSrcRange<Dst,
+ Src,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_SIGNED> {
+ static const NumericRangeRepresentation value = NUMERIC_RANGE_NOT_CONTAINED;
+};
+
+enum RangeConstraint {
+ RANGE_VALID = 0x0, // Value can be represented by the destination type.
+ RANGE_UNDERFLOW = 0x1, // Value would overflow.
+ RANGE_OVERFLOW = 0x2, // Value would underflow.
+ RANGE_INVALID = RANGE_UNDERFLOW | RANGE_OVERFLOW // Invalid (i.e. NaN).
+};
+
+// Helper function for coercing an int back to a RangeContraint.
+inline RangeConstraint GetRangeConstraint(int integer_range_constraint) {
+ DCHECK(integer_range_constraint >= RANGE_VALID &&
+ integer_range_constraint <= RANGE_INVALID);
+ return static_cast<RangeConstraint>(integer_range_constraint);
+}
+
+// This function creates a RangeConstraint from an upper and lower bound
+// check by taking advantage of the fact that only NaN can be out of range in
+// both directions at once.
+inline RangeConstraint GetRangeConstraint(bool is_in_upper_bound,
+ bool is_in_lower_bound) {
+ return GetRangeConstraint((is_in_upper_bound ? 0 : RANGE_OVERFLOW) |
+ (is_in_lower_bound ? 0 : RANGE_UNDERFLOW));
+}
+
+// The following helper template addresses a corner case in range checks for
+// conversion from a floating-point type to an integral type of smaller range
+// but larger precision (e.g. float -> unsigned). The problem is as follows:
+// 1. Integral maximum is always one less than a power of two, so it must be
+// truncated to fit the mantissa of the floating point. The direction of
+// rounding is implementation defined, but by default it's always IEEE
+// floats, which round to nearest and thus result in a value of larger
+// magnitude than the integral value.
+// Example: float f = UINT_MAX; // f is 4294967296f but UINT_MAX
+// // is 4294967295u.
+// 2. If the floating point value is equal to the promoted integral maximum
+// value, a range check will erroneously pass.
+// Example: (4294967296f <= 4294967295u) // This is true due to a precision
+// // loss in rounding up to float.
+// 3. When the floating point value is then converted to an integral, the
+// resulting value is out of range for the target integral type and
+// thus is implementation defined.
+// Example: unsigned u = (float)INT_MAX; // u will typically overflow to 0.
+// To fix this bug we manually truncate the maximum value when the destination
+// type is an integral of larger precision than the source floating-point type,
+// such that the resulting maximum is represented exactly as a floating point.
+template <typename Dst, typename Src>
+struct NarrowingRange {
+ typedef typename std::numeric_limits<Src> SrcLimits;
+ typedef typename std::numeric_limits<Dst> DstLimits;
+
+ static Dst max() {
+ // The following logic avoids warnings where the max function is
+ // instantiated with invalid values for a bit shift (even though
+ // such a function can never be called).
+ static const int shift =
+ (MaxExponent<Src>::value > MaxExponent<Dst>::value &&
+ SrcLimits::digits < DstLimits::digits && SrcLimits::is_iec559 &&
+ DstLimits::is_integer)
+ ? (DstLimits::digits - SrcLimits::digits)
+ : 0;
+
+ // We use UINTMAX_C below to avoid compiler warnings about shifting floating
+ // points. Since it's a compile time calculation, it shouldn't have any
+ // performance impact.
+ return DstLimits::max() - static_cast<Dst>((UINTMAX_C(1) << shift) - 1);
+ }
+
+ static Dst min() {
+ return std::numeric_limits<Dst>::is_iec559 ? -DstLimits::max()
+ : DstLimits::min();
+ }
+};
+
+template <
+ typename Dst,
+ typename Src,
+ IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED,
+ IntegerRepresentation SrcSign = std::numeric_limits<Src>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED,
+ NumericRangeRepresentation DstRange =
+ StaticDstRangeRelationToSrcRange<Dst, Src>::value >
+struct DstRangeRelationToSrcRangeImpl;
+
+// The following templates are for ranges that must be verified at runtime. We
+// split it into checks based on signedness to avoid confusing casts and
+// compiler warnings on signed an unsigned comparisons.
+
+// Dst range is statically determined to contain Src: Nothing to check.
+template <typename Dst,
+ typename Src,
+ IntegerRepresentation DstSign,
+ IntegerRepresentation SrcSign>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ DstSign,
+ SrcSign,
+ NUMERIC_RANGE_CONTAINED> {
+ static RangeConstraint Check(Src value) { return RANGE_VALID; }
+};
+
+// Signed to signed narrowing: Both the upper and lower boundaries may be
+// exceeded.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_SIGNED,
+ INTEGER_REPRESENTATION_SIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return GetRangeConstraint((value <= NarrowingRange<Dst, Src>::max()),
+ (value >= NarrowingRange<Dst, Src>::min()));
+ }
+};
+
+// Unsigned to unsigned narrowing: Only the upper boundary can be exceeded.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return GetRangeConstraint(value <= NarrowingRange<Dst, Src>::max(), true);
+ }
+};
+
+// Unsigned to signed: The upper boundary may be exceeded.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_SIGNED,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return sizeof(Dst) > sizeof(Src)
+ ? RANGE_VALID
+ : GetRangeConstraint(
+ value <= static_cast<Src>(NarrowingRange<Dst, Src>::max()),
+ true);
+ }
+};
+
+// Signed to unsigned: The upper boundary may be exceeded for a narrower Dst,
+// and any negative value exceeds the lower boundary.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_SIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return (MaxExponent<Dst>::value >= MaxExponent<Src>::value)
+ ? GetRangeConstraint(true, value >= static_cast<Src>(0))
+ : GetRangeConstraint(
+ value <= static_cast<Src>(NarrowingRange<Dst, Src>::max()),
+ value >= static_cast<Src>(0));
+ }
+};
+
+template <typename Dst, typename Src>
+inline RangeConstraint DstRangeRelationToSrcRange(Src value) {
+ static_assert(std::numeric_limits<Src>::is_specialized,
+ "Argument must be numeric.");
+ static_assert(std::numeric_limits<Dst>::is_specialized,
+ "Result must be numeric.");
+ return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
+}
+
+} // namespace internal
+} // namespace base
+
+#endif // BASE_NUMERICS_SAFE_CONVERSIONS_IMPL_H_