1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___CONFIGURATION_HARDENING_H
10#define _LIBCPP___CONFIGURATION_HARDENING_H
11
12#include <__config_site>
13#include <__configuration/experimental.h>
14#include <__configuration/language.h>
15
16#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
17# pragma GCC system_header
18#endif
19
20// TODO(LLVM 23): Remove this. We're making these an error to catch folks who might not have migrated.
21// Since hardening went through several changes (many of which impacted user-facing macros),
22// we're keeping these checks around for a bit longer than usual. Failure to properly configure
23// hardening results in checks being dropped silently, which is a pretty big deal.
24#if defined(_LIBCPP_ENABLE_ASSERTIONS)
25# error "_LIBCPP_ENABLE_ASSERTIONS has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
26#endif
27#if defined(_LIBCPP_ENABLE_HARDENED_MODE)
28# error "_LIBCPP_ENABLE_HARDENED_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
29#endif
30#if defined(_LIBCPP_ENABLE_SAFE_MODE)
31# error "_LIBCPP_ENABLE_SAFE_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
32#endif
33#if defined(_LIBCPP_ENABLE_DEBUG_MODE)
34# error "_LIBCPP_ENABLE_DEBUG_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
35#endif
36
37// The library provides the macro `_LIBCPP_HARDENING_MODE` which can be set to one of the following values:
38//
39// - `_LIBCPP_HARDENING_MODE_NONE`;
40// - `_LIBCPP_HARDENING_MODE_FAST`;
41// - `_LIBCPP_HARDENING_MODE_EXTENSIVE`;
42// - `_LIBCPP_HARDENING_MODE_DEBUG`.
43//
44// These values have the following effects:
45//
46// - `_LIBCPP_HARDENING_MODE_NONE` -- sets the hardening mode to "none" which disables all runtime hardening checks;
47//
48// - `_LIBCPP_HARDENING_MODE_FAST` -- sets that hardening mode to "fast". The fast mode enables security-critical checks
49// that can be done with relatively little runtime overhead in constant time;
50//
51// - `_LIBCPP_HARDENING_MODE_EXTENSIVE` -- sets the hardening mode to "extensive". The extensive mode is a superset of
52// the fast mode that additionally enables checks that are relatively cheap and prevent common types of logic errors
53// but are not necessarily security-critical;
54//
55// - `_LIBCPP_HARDENING_MODE_DEBUG` -- sets the hardening mode to "debug". The debug mode is a superset of the extensive
56// mode and enables all checks available in the library, including internal assertions. Checks that are part of the
57// debug mode can be very expensive and thus the debug mode is intended to be used for testing, not in production.
58
59// Inside the library, assertions are categorized so they can be cherry-picked based on the chosen hardening mode. These
60// macros are only for internal use -- users should only pick one of the high-level hardening modes described above.
61//
62// - `_LIBCPP_ASSERT_VALID_INPUT_RANGE` -- checks that ranges (whether expressed as an iterator pair, an iterator and
63// a sentinel, an iterator and a count, or a `std::range`) given as input to library functions are valid:
64// - the sentinel is reachable from the begin iterator;
65// - TODO(hardening): both iterators refer to the same container.
66//
67// - `_LIBCPP_ASSERT_VALID_ELEMENT_ACCESS` -- checks that any attempts to access a container element, whether through
68// the container object or through an iterator, are valid and do not attempt to go out of bounds or otherwise access
69// a non-existent element. For iterator checks to work, bounded iterators must be enabled in the ABI. Types like
70// `optional` and `function` are considered one-element containers for the purposes of this check.
71//
72// - `_LIBCPP_ASSERT_NON_NULL` -- checks that the pointer being dereferenced is not null. On most modern platforms zero
73// address does not refer to an actual location in memory, so a null pointer dereference would not compromize the
74// memory security of a program (however, it is still undefined behavior that can result in strange errors due to
75// compiler optimizations).
76//
77// - `_LIBCPP_ASSERT_NON_OVERLAPPING_RANGES` -- for functions that take several ranges as arguments, checks that the
78// given ranges do not overlap.
79//
80// - `_LIBCPP_ASSERT_VALID_DEALLOCATION` -- checks that an attempt to deallocate memory is valid (e.g. the given object
81// was allocated by the given allocator). Violating this category typically results in a memory leak.
82//
83// - `_LIBCPP_ASSERT_VALID_EXTERNAL_API_CALL` -- checks that a call to an external API doesn't fail in
84// an unexpected manner. This includes triggering documented cases of undefined behavior in an external library (like
85// attempting to unlock an unlocked mutex in pthreads). Any API external to the library falls under this category
86// (from system calls to compiler intrinsics). We generally don't expect these failures to compromize memory safety or
87// otherwise create an immediate security issue.
88//
89// - `_LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR` -- checks any operations that exchange nodes between containers to make sure
90// the containers have compatible allocators.
91//
92// - `_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN` -- checks that the given argument is within the domain of valid arguments
93// for the function. Violating this typically produces an incorrect result (e.g. the clamp algorithm returns the
94// original value without clamping it due to incorrect functors) or puts an object into an invalid state (e.g.
95// a string view where only a subset of elements is possible to access). This category is for assertions violating
96// which doesn't cause any immediate issues in the library -- whatever the consequences are, they will happen in the
97// user code.
98//
99// - `_LIBCPP_ASSERT_PEDANTIC` -- checks prerequisites which are imposed by the Standard, but violating which happens to
100// be benign in our implementation.
101//
102// - `_LIBCPP_ASSERT_SEMANTIC_REQUIREMENT` -- checks that the given argument satisfies the semantic requirements imposed
103// by the Standard. Typically, there is no simple way to completely prove that a semantic requirement is satisfied;
104// thus, this would often be a heuristic check and it might be quite expensive.
105//
106// - `_LIBCPP_ASSERT_INTERNAL` -- checks that internal invariants of the library hold. These assertions don't depend on
107// user input.
108//
109// - `_LIBCPP_ASSERT_UNCATEGORIZED` -- for assertions that haven't been properly classified yet.
110
111// clang-format off
112# define _LIBCPP_HARDENING_MODE_NONE (1 << 1)
113# define _LIBCPP_HARDENING_MODE_FAST (1 << 2)
114# define _LIBCPP_HARDENING_MODE_EXTENSIVE (1 << 4) // Deliberately not ordered.
115# define _LIBCPP_HARDENING_MODE_DEBUG (1 << 3)
116// clang-format on
117
118#ifndef _LIBCPP_HARDENING_MODE
119
120# ifndef _LIBCPP_HARDENING_MODE_DEFAULT
121# error _LIBCPP_HARDENING_MODE_DEFAULT is not defined. This definition should be set at configuration time in the \
122`__config_site` header, please make sure your installation of libc++ is not broken.
123# endif
124
125# define _LIBCPP_HARDENING_MODE _LIBCPP_HARDENING_MODE_DEFAULT
126#endif
127
128#if _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_NONE && _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_FAST && \
129 _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_EXTENSIVE && \
130 _LIBCPP_HARDENING_MODE != _LIBCPP_HARDENING_MODE_DEBUG
131# error _LIBCPP_HARDENING_MODE must be set to one of the following values: \
132_LIBCPP_HARDENING_MODE_NONE, \
133_LIBCPP_HARDENING_MODE_FAST, \
134_LIBCPP_HARDENING_MODE_EXTENSIVE, \
135_LIBCPP_HARDENING_MODE_DEBUG
136#endif
137
138// The library provides the macro `_LIBCPP_ASSERTION_SEMANTIC` for configuring the assertion semantic used by hardening;
139// it can be set to one of the following values:
140//
141// - `_LIBCPP_ASSERTION_SEMANTIC_IGNORE`;
142// - `_LIBCPP_ASSERTION_SEMANTIC_OBSERVE`;
143// - `_LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE`;
144// - `_LIBCPP_ASSERTION_SEMANTIC_ENFORCE`.
145//
146// libc++ assertion semantics generally mirror the evaluation semantics of C++26 Contracts:
147// - `ignore` evaluates the assertion but doesn't do anything if it fails (note that it differs from the Contracts
148// `ignore` semantic which wouldn't evaluate the assertion at all);
149// - `observe` logs an error (indicating, if possible, that the error is fatal) and continues execution;
150// - `quick-enforce` terminates the program as fast as possible (via trapping);
151// - `enforce` logs an error and then terminates the program.
152//
153// Additionally, a special `hardening-dependent` value selects the assertion semantic based on the hardening mode in
154// effect: the production-capable modes (`fast` and `extensive`) map to `quick_enforce` and the `debug` mode maps to
155// `enforce`. The `hardening-dependent` semantic cannot be selected explicitly, it is only used when no assertion
156// semantic is provided by the user _and_ the library's default semantic is configured to be dependent on hardening.
157//
158// Notes:
159// - Continuing execution after a hardening check fails results in undefined behavior; the `observe` semantic is meant
160// to make adopting hardening easier but should not be used outside of this scenario;
161// - C++26 wording for Library Hardening precludes a conforming Hardened implementation from using the Contracts
162// `ignore` semantic when evaluating hardened preconditions in the Library. Libc++ allows using this semantic for
163// hardened preconditions, however, be aware that using `ignore` does not produce a conforming "Hardened"
164// implementation, unlike the other semantics above.
165// clang-format off
166# define _LIBCPP_ASSERTION_SEMANTIC_HARDENING_DEPENDENT (1 << 1)
167# define _LIBCPP_ASSERTION_SEMANTIC_IGNORE (1 << 2)
168# define _LIBCPP_ASSERTION_SEMANTIC_OBSERVE (1 << 3)
169# define _LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE (1 << 4)
170# define _LIBCPP_ASSERTION_SEMANTIC_ENFORCE (1 << 5)
171// clang-format on
172
173// If the user attempts to configure the assertion semantic, check that it is allowed in the current environment.
174#if defined(_LIBCPP_ASSERTION_SEMANTIC)
175# if !_LIBCPP_HAS_EXPERIMENTAL_LIBRARY
176# error "Assertion semantics are an experimental feature."
177# endif
178# if defined(_LIBCPP_CXX03_LANG)
179# error "Assertion semantics are not available in the C++03 mode."
180# endif
181#endif // defined(_LIBCPP_ASSERTION_SEMANTIC)
182
183// User-provided semantic takes top priority -- don't override if set.
184#ifndef _LIBCPP_ASSERTION_SEMANTIC
185
186# ifndef _LIBCPP_ASSERTION_SEMANTIC_DEFAULT
187# error _LIBCPP_ASSERTION_SEMANTIC_DEFAULT is not defined. This definition should be set at configuration time in \
188the `__config_site` header, please make sure your installation of libc++ is not broken.
189# endif
190
191# if _LIBCPP_ASSERTION_SEMANTIC_DEFAULT != _LIBCPP_ASSERTION_SEMANTIC_HARDENING_DEPENDENT
192# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_DEFAULT
193# else
194# if _LIBCPP_HARDENING_MODE == _LIBCPP_HARDENING_MODE_DEBUG
195# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_ENFORCE
196# else
197# define _LIBCPP_ASSERTION_SEMANTIC _LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE
198# endif
199# endif // _LIBCPP_ASSERTION_SEMANTIC_DEFAULT != _LIBCPP_ASSERTION_SEMANTIC_HARDENING_DEPENDENT
200
201#endif // #ifndef _LIBCPP_ASSERTION_SEMANTIC
202
203// Finally, validate the selected semantic (in case the user tries setting it to an incorrect value):
204#if _LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_IGNORE && \
205 _LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_OBSERVE && \
206 _LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE && \
207 _LIBCPP_ASSERTION_SEMANTIC != _LIBCPP_ASSERTION_SEMANTIC_ENFORCE
208# error _LIBCPP_ASSERTION_SEMANTIC must be set to one of the following values: \
209_LIBCPP_ASSERTION_SEMANTIC_IGNORE, \
210_LIBCPP_ASSERTION_SEMANTIC_OBSERVE, \
211_LIBCPP_ASSERTION_SEMANTIC_QUICK_ENFORCE, \
212_LIBCPP_ASSERTION_SEMANTIC_ENFORCE
213#endif
214
215#endif // _LIBCPP___CONFIGURATION_HARDENING_H
216