1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 // Functions to help with verifying various |Mojo...Options| structs from the
6 // (public, C) API. These are "extensible" structs, which all have |struct_size|
7 // as their first member. All fields (other than |struct_size|) are optional,
8 // but any |flags| specified must be known to the system (otherwise, an error of
9 // |MOJO_RESULT_UNIMPLEMENTED| should be returned).
10
11 #ifndef MOJO_SYSTEM_OPTIONS_VALIDATION_H_
12 #define MOJO_SYSTEM_OPTIONS_VALIDATION_H_
13
14 #include <stddef.h>
15 #include <stdint.h>
16
17 #include "base/macros.h"
18 #include "mojo/public/c/system/types.h"
19 #include "mojo/system/memory.h"
20 #include "mojo/system/system_impl_export.h"
21
22 namespace mojo {
23 namespace system {
24
25 // Checks that |buffer| appears to contain a valid Options struct, namely
26 // properly aligned and with a |struct_size| field (which must the first field
27 // of the struct and be a |uint32_t|) containing a plausible size.
28 template <class Options>
IsOptionsStructPointerAndSizeValid(const void * buffer)29 bool IsOptionsStructPointerAndSizeValid(const void* buffer) {
30 COMPILE_ASSERT(offsetof(Options, struct_size) == 0,
31 Options_struct_size_not_first_member);
32 // TODO(vtl): With C++11, use |sizeof(Options::struct_size)| instead.
33 COMPILE_ASSERT(sizeof(static_cast<const Options*>(buffer)->struct_size) ==
34 sizeof(uint32_t),
35 Options_struct_size_not_32_bits);
36
37 // Note: Use |MOJO_ALIGNOF()| here to match the exact macro used in the
38 // declaration of Options structs.
39 if (!internal::VerifyUserPointerHelper<sizeof(uint32_t),
40 MOJO_ALIGNOF(Options)>(buffer))
41 return false;
42
43 return static_cast<const Options*>(buffer)->struct_size >= sizeof(uint32_t);
44 }
45
46 // Checks that the Options struct in |buffer| has a member with the given offset
47 // and size. This may be called only if |IsOptionsStructPointerAndSizeValid()|
48 // returned true.
49 //
50 // You may want to use the macro |HAS_OPTIONS_STRUCT_MEMBER()| instead.
51 template <class Options, size_t offset, size_t size>
HasOptionsStructMember(const void * buffer)52 bool HasOptionsStructMember(const void* buffer) {
53 // We assume that |offset| and |size| are reasonable, since they should come
54 // from |offsetof(Options, some_member)| and |sizeof(Options::some_member)|,
55 // respectively.
56 return static_cast<const Options*>(buffer)->struct_size >=
57 offset + size;
58 }
59
60 // Macro to invoke |HasOptionsStructMember()| parametrized by member name
61 // instead of offset and size.
62 //
63 // (We can't just give |HasOptionsStructMember()| a member pointer template
64 // argument instead, since there's no good/strictly-correct way to get an offset
65 // from that.)
66 //
67 // TODO(vtl): With C++11, use |sizeof(Options::member)| instead.
68 #define HAS_OPTIONS_STRUCT_MEMBER(Options, member, buffer) \
69 (HasOptionsStructMember< \
70 Options, \
71 offsetof(Options, member), \
72 sizeof(static_cast<const Options*>(buffer)->member)>(buffer))
73
74 // Checks that the (standard) |flags| member consists of only known flags. This
75 // should only be called if |HAS_OPTIONS_STRUCT_MEMBER()| returned true for the
76 // |flags| field.
77 //
78 // The rationale for *not* ignoring these flags is that the caller should have a
79 // way of specifying that certain options not be ignored. E.g., one may have a
80 // |MOJO_..._OPTIONS_FLAG_DONT_IGNORE_FOO| flag and a |foo| member; if the flag
81 // is set, it will guarantee that the version of the system knows about the
82 // |foo| member (and won't ignore it).
83 template <class Options>
AreOptionsFlagsAllKnown(const void * buffer,uint32_t known_flags)84 bool AreOptionsFlagsAllKnown(const void* buffer, uint32_t known_flags) {
85 return (static_cast<const Options*>(buffer)->flags & ~known_flags) == 0;
86 }
87
88 // Does basic cursory checks on |in_options| (|struct_size| and |flags|; |flags|
89 // must immediately follow |struct_size|); |in_options| must be non-null. The
90 // following should be done before calling this:
91 // - Set |out_options| to the default options.
92 // - If |in_options| is null, don't continue (success).
93 // This function then:
94 // - Checks if (according to |IsOptionsStructPointerAndSizeValid()|),
95 // |struct_size| is valid; if not returns |MOJO_RESULT_INVALID_ARGUMENT|.
96 // - If |in_options| has a |flags| field, checks that it only has
97 // |known_flags| set; if so copies it to |out_options->flags|, and if not
98 // returns |MOJO_RESULT_UNIMPLEMENTED|.
99 // - At this point, returns |MOJO_RESULT_OK|.
100 template <class Options>
ValidateOptionsStructPointerSizeAndFlags(const Options * in_options,uint32_t known_flags,Options * out_options)101 MojoResult ValidateOptionsStructPointerSizeAndFlags(
102 const Options* in_options,
103 uint32_t known_flags,
104 Options* out_options) {
105 COMPILE_ASSERT(offsetof(Options, flags) == sizeof(uint32_t),
106 Options_flags_doesnt_immediately_follow_struct_size);
107
108 if (!IsOptionsStructPointerAndSizeValid<Options>(in_options))
109 return MOJO_RESULT_INVALID_ARGUMENT;
110
111 if (HAS_OPTIONS_STRUCT_MEMBER(Options, flags, in_options)) {
112 if (!AreOptionsFlagsAllKnown<Options>(in_options, known_flags))
113 return MOJO_RESULT_UNIMPLEMENTED;
114 out_options->flags = in_options->flags;
115 }
116
117 return MOJO_RESULT_OK;
118 }
119
120 } // namespace system
121 } // namespace mojo
122
123 #endif // MOJO_SYSTEM_OPTIONS_VALIDATION_H_
124