zero_memory source code

1 /*
2 The MIT License (MIT)
3 
4 Copyright (c) 2019 DarkRiDDeR
5 
6 Permission is hereby granted, free of charge, to any person obtaining a copy
7 of this software and associated documentation files (the "Software"), to deal
8 in the Software without restriction, including without limitation the rights
9 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10 copies of the Software, and to permit persons to whom the Software is
11 furnished to do so, subject to the following conditions:
12 
13 The above copyright notice and this permission notice shall be included in all
14 copies or substantial portions of the Software.
15 
16 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22 SOFTWARE.
23 */
24 
25 module zero_memory;
26 
27 /**
28 * Fills a block of memory with zeros. It is designed to be a more secure version of ZeroMemory.
29 *
30 * !!! function secureZeroMemory processes data by byte.
31 *
32 * Use this function instead of ZeroMemory when you want to ensure that your data will be overwritten promptly,
33 * as some compilers can optimize a call to ZeroMemory by removing it entirely.
34 */
35 void secureZeroMemory (void *p, in size_t length)
36 pure nothrow @nogc
37 {
38     version (D_InlineAsm_X86_64)
39     {
40         asm
41         pure nothrow @nogc
42         {
43             mov RBX, [p];
44             mov RDX, p;
45             mov RCX, length;
46             iter:
47             xor RBX, RBX;
48             mov [RDX], RBX;
49             inc RDX;
50             loop iter;
51         }
52     }
53     else version (D_InlineAsm_X86)
54     {
55         asm
56         pure nothrow @nogc
57         {
58             mov EBX, [p];
59             mov EDX, p;
60             mov ECX, length;
61             iter:
62             xor EBX, EBX;
63             mov [EDX], EBX;
64             inc EDX;
65             loop iter;
66         }
67     }
68     else version (LDC)
69     {
70         import ldc.intrinsics : llvm_memset;
71         llvm_memset(p, 0, length, true); // The "true" means volatile.
72     }
73     else
74     {
75         static if (__VERSION__ >= 2089)
76             import core..volatile : volatileStore;
77         else
78             import core.bitop : volatileStore;
79         static void zero(void* p, size_t remaining) @nogc nothrow
80         {
81             for (; remaining != 0 && (cast(size_t) p) % size_t.alignof != 0; ++p, --remaining)
82                 volatileStore(cast(ubyte*) p, ubyte(0));
83             for (; remaining >= size_t.sizeof; p += size_t.sizeof, remaining -= size_t.sizeof)
84                 volatileStore(cast(size_t*) p, size_t(0));
85             for (; remaining != 0; ++p, --remaining)
86                 volatileStore(cast(ubyte*) p, ubyte(0));
87         }
88         // Workaround because volatileStore is not annotated "pure".
89         (cast(void function(void*, size_t) @nogc nothrow pure) &zero)(p, length);
90     }
91 }
92 
93 void secureZeroMemory (void[] ar)
94 pure nothrow @nogc
95 {
96     if (ar.length == 0)
97         return;
98 
99     secureZeroMemory(ar.ptr, ar.length);
100 }
101 
102 
103 unittest
104 {
105     auto ar = new ubyte[255];
106     auto ar2 = ar.dup;
107 
108     foreach (i, ref e; ar2)
109         e = cast(ubyte)i;
110     assert(ar != ar2);
111 
112     secureZeroMemory(ar2.ptr, ar2.length);
113     assert(ar == ar2);
114 
115 
116     uint[] i  = [0, 0, 0,  0, 0 ];
117     uint[] i2 = [8, 5, 99, 5, 99];
118     // !!! function secureZeroMemory processes data by byte. Therefore, it is wrong:
119     secureZeroMemory(i2.ptr, i2.length);
120     assert(i != i2);
121     // Need to calculate the length:
122     secureZeroMemory(i2.ptr, uint.sizeof * i2.length);
123     assert(i == i2);
124 
125     // or use a cast to type void[]
126     i2 = [8, 5, 99, 5, 99];
127     secureZeroMemory(cast(void[])i2);
128     assert(i == i2);
129 }