api_impl/
mem.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
// Copyright 2024 The Fuchsia Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

pub fn malloc(size: usize, _hint: u32) -> *mut ::std::os::raw::c_void {
    // The 'hint' parameter allows requesting memory that is zeroed and that's
    // not shared with other TAs. We always zero allocations and don't share
    // memory with other TAs so we ignore the hint.
    unsafe { libc::malloc(size) }
}

/// # Safety
///
/// This wraps libc::realloc and is only safe to call with a pointer value that is NULL or allocated
/// through malloc / realloc.
pub unsafe fn realloc(
    buffer: *mut ::std::os::raw::c_void,
    new_size: usize,
) -> *mut ::std::os::raw::c_void {
    libc::realloc(buffer, new_size)
}

/// # Safety
///
/// This wraps libc::free and is only safe to call with a pointer value that is NULL or allocated
/// through malloc / realloc.
pub unsafe fn free(buffer: *mut ::std::os::raw::c_void) {
    libc::free(buffer)
}

pub fn mem_move(dest: *mut ::std::os::raw::c_void, src: *mut ::std::os::raw::c_void, size: usize) {
    // The spec does not define the behaviour of this function when the size is
    // zero (ditto for libc's memmove). However, there are xtest cases that
    // explicitly rely on being able to do this(!) (with null pointers even),
    // so better for this implementation to regard that as a no-op.
    if size == 0 {
        return;
    }

    // The spec also does not define the behavior of this function when either
    // pointer is null - but at the very least this is a condition of
    // std::ptr::copy, so check that here for a clearer panic.
    assert!(!src.is_null());
    assert!(!dest.is_null());

    // This is semantically equivalent to libc::memmove() with the order of operands reversed.
    // This uses the Rust library routine instead so that it can be optimized directly if the
    // toolchain decides, calling libc::memmove() would require an external library call here.
    unsafe { std::ptr::copy(src as *const u8, dest as *mut u8, size) }
}

pub fn mem_compare(
    buffer1: *mut ::std::os::raw::c_void,
    buffer2: *mut ::std::os::raw::c_void,
    size: usize,
) -> i32 {
    // The spec does not define the behavior of this function when either
    // pointer is null - but at the very least this is a condition of
    // std::slice::from_raw_parts, so check that here for a clearer panic.
    assert!(!buffer1.is_null());
    assert!(!buffer2.is_null());

    unsafe {
        let buffer1 = std::slice::from_raw_parts::<u8>(buffer1 as *const u8, size);
        let buffer2 = std::slice::from_raw_parts::<u8>(buffer2 as *const u8, size);
        match buffer1.cmp(buffer2) {
            std::cmp::Ordering::Less => -1,
            std::cmp::Ordering::Equal => 0,
            std::cmp::Ordering::Greater => 1,
        }
    }
}

pub fn mem_fill(buffer: *mut ::std::os::raw::c_void, x: u8, size: usize) {
    // The spec does not define the behavior of this function when the pointer
    // is null - but at the very least this is a condition of
    //std::ptr::write_bytes, so check that here for a clearer panic.
    assert!(!buffer.is_null());

    // This is semantically equivalent to libc::memset() as it's called with a byte sized type.
    // This uses the Rust library routine instead so that it can be optimized directly if the
    // toolchain decides, calling libc::memmove() would require an external library call here.
    unsafe { std::ptr::write_bytes(buffer as *mut u8, x, size) }
}

#[no_mangle]
pub extern "C" fn __scudo_default_options() -> *const std::ffi::c_char {
    b"zero_contents=true\0" as *const u8 as *const std::ffi::c_char
}

#[cfg(test)]
mod test {
    use super::*;
    use std::ffi::c_void;

    fn check_memory_contains(addr: *const c_void, fill: u8, len: usize) {
        for i in 0..len as isize {
            let val = unsafe { std::ptr::read_volatile(addr.byte_offset(i) as *const u8) };
            assert_eq!(val, fill, "offset {i}");
        }
    }

    fn fill_memory(addr: *mut c_void, fill: u8, len: usize) {
        for i in 0..len as isize {
            unsafe { std::ptr::write_volatile(addr.byte_offset(i) as *mut u8, fill) }
        }
    }

    #[fuchsia::test]
    fn malloc_free() {
        const ALLOC_SIZE: usize = 25;
        let buf = malloc(ALLOC_SIZE, 0);
        assert_ne!(buf, std::ptr::null_mut());

        unsafe { free(buf) };
    }

    #[fuchsia::test]
    fn small_malloc_zeroed() {
        const ALLOC_SIZE: usize = 25;
        let buf = malloc(ALLOC_SIZE, 0);
        assert_ne!(buf, std::ptr::null_mut());

        check_memory_contains(buf, 0, ALLOC_SIZE);

        // Fill memory and then free/malloc to check that if the memory is reused for the
        // new allocation that it's still zeroed out.
        fill_memory(buf, 7u8, ALLOC_SIZE);
        unsafe { free(buf) };
        let buf = malloc(ALLOC_SIZE, 0);
        assert_ne!(buf, std::ptr::null_mut());
        check_memory_contains(buf, 0, ALLOC_SIZE);
        unsafe { free(buf) };
    }

    #[fuchsia::test]
    fn large_malloc_zeroed() {
        const ALLOC_SIZE: usize = 1024 * 1024 + 1;
        let buf = malloc(ALLOC_SIZE, 0);
        assert_ne!(buf, std::ptr::null_mut());
        check_memory_contains(buf, 0, ALLOC_SIZE);
        fill_memory(buf, 7u8, ALLOC_SIZE);
        unsafe { free(buf) };
        let buf = malloc(ALLOC_SIZE, 0);
        check_memory_contains(buf, 0, ALLOC_SIZE);
        unsafe { free(buf) };
    }

    #[fuchsia::test]
    fn realloc_grow() {
        let buf = malloc(5, 0);
        assert_ne!(buf, std::ptr::null_mut());
        fill_memory(buf, 7u8, 5);
        let realloced_buf = unsafe { realloc(buf, 5 * 1024) };
        assert_ne!(realloced_buf as usize, 0);
        check_memory_contains(realloced_buf, 7u8, 5);
        check_memory_contains(unsafe { realloced_buf.byte_offset(5) }, 0, 5 * 1024 - 5);

        unsafe { free(realloced_buf) };
    }

    #[fuchsia::test]
    fn realloc_shrink() {
        let buf = malloc(5 * 1024, 0);
        assert_ne!(buf, std::ptr::null_mut());
        fill_memory(buf, 7u8, 5 * 1024);
        let realloced_buf = unsafe { realloc(buf, 5) };
        assert_ne!(realloced_buf, std::ptr::null_mut());
        check_memory_contains(realloced_buf, 7, 5);
        unsafe {
            free(realloced_buf);
        }
    }

    // See note at top of implementation.
    #[fuchsia::test]
    fn mem_move_size_zero() {
        mem_move(std::ptr::null_mut(), std::ptr::null_mut(), 0);

        let nonnull = malloc(10, 0);
        mem_move(nonnull, std::ptr::null_mut(), 0);
        mem_move(std::ptr::null_mut(), nonnull, 0);

        unsafe { free(nonnull) };
    }

    #[fuchsia::test]
    fn mem_move_overlap() {
        // Allocate a buffer 12 bytes long and initialize the first 8 elements, then move 8 bytes from
        // the start of the buffer to an offset of 4 from the start.
        let buf = malloc(12, 0);
        assert_ne!(buf, std::ptr::null_mut());
        fill_memory(buf, 1, 4);
        fill_memory(unsafe { buf.byte_offset(4) }, 2, 4);
        let dest = unsafe { buf.byte_offset(4) };
        mem_move(dest, buf, 8);
        check_memory_contains(buf, 1, 4);
        check_memory_contains(unsafe { buf.byte_offset(4) }, 1, 4);
        check_memory_contains(unsafe { buf.byte_offset(8) }, 2, 4);
        unsafe { free(buf) };
    }

    #[fuchsia::test]
    fn mem_fill_nonzero() {
        let buf = malloc(5, 0);
        assert_ne!(buf, std::ptr::null_mut());
        mem_fill(buf, 0x42, 5);
        check_memory_contains(buf, 0x42, 5);
        unsafe { free(buf) };
    }

    #[fuchsia::test]
    fn mem_compare_tests() {
        let a = &mut [1u8, 2, 3];
        let b = &mut [2u8, 2, 3];
        let c = &mut [2u8, 2, 4];
        let a_ptr = a.as_mut_ptr() as *mut c_void;
        let b_ptr = b.as_mut_ptr() as *mut c_void;
        let c_ptr = c.as_mut_ptr() as *mut c_void;

        assert_eq!(mem_compare(a_ptr, a_ptr, 1), 0);
        assert_eq!(mem_compare(a_ptr, a_ptr, 3), 0);
        assert_eq!(mem_compare(a_ptr, b_ptr, 1), -1);
        assert_eq!(mem_compare(b_ptr, a_ptr, 1), 1);
        assert_eq!(mem_compare(b_ptr, c_ptr, 2), 0);
        assert_eq!(mem_compare(b_ptr, c_ptr, 3), -1);
    }
}