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
|
// SPDX-License-Identifier: GPL-2.0
//! User pointers.
//!
//! C header: [`include/linux/uaccess.h`](../../../../include/linux/uaccess.h)
use crate::{
bindings,
error::code::*,
io_buffer::{IoBufferReader, IoBufferWriter},
Result,
};
use alloc::vec::Vec;
/// A reference to an area in userspace memory, which can be either
/// read-only or read-write.
///
/// All methods on this struct are safe: invalid pointers return
/// `EFAULT`. Concurrent access, *including data races to/from userspace
/// memory*, is permitted, because fundamentally another userspace
/// thread/process could always be modifying memory at the same time
/// (in the same way that userspace Rust's [`std::io`] permits data races
/// with the contents of files on disk). In the presence of a race, the
/// exact byte values read/written are unspecified but the operation is
/// well-defined. Kernelspace code should validate its copy of data
/// after completing a read, and not expect that multiple reads of the
/// same address will return the same value.
///
/// All APIs enforce the invariant that a given byte of memory from userspace
/// may only be read once. By preventing double-fetches we avoid TOCTOU
/// vulnerabilities. This is accomplished by taking `self` by value to prevent
/// obtaining multiple readers on a given [`UserSlicePtr`], and the readers
/// only permitting forward reads.
///
/// Constructing a [`UserSlicePtr`] performs no checks on the provided
/// address and length, it can safely be constructed inside a kernel thread
/// with no current userspace process. Reads and writes wrap the kernel APIs
/// `copy_from_user` and `copy_to_user`, which check the memory map of the
/// current process and enforce that the address range is within the user
/// range (no additional calls to `access_ok` are needed).
///
/// [`std::io`]: https://doc.rust-lang.org/std/io/index.html
pub struct UserSlicePtr(*mut core::ffi::c_void, usize);
impl UserSlicePtr {
/// Constructs a user slice from a raw pointer and a length in bytes.
///
/// # Safety
///
/// Callers must be careful to avoid time-of-check-time-of-use
/// (TOCTOU) issues. The simplest way is to create a single instance of
/// [`UserSlicePtr`] per user memory block as it reads each byte at
/// most once.
pub unsafe fn new(ptr: *mut core::ffi::c_void, length: usize) -> Self {
UserSlicePtr(ptr, length)
}
/// Reads the entirety of the user slice.
///
/// Returns `EFAULT` if the address does not currently point to
/// mapped, readable memory.
pub fn read_all(self) -> Result<Vec<u8>> {
self.reader().read_all()
}
/// Constructs a [`UserSlicePtrReader`].
pub fn reader(self) -> UserSlicePtrReader {
UserSlicePtrReader(self.0, self.1)
}
/// Writes the provided slice into the user slice.
///
/// Returns `EFAULT` if the address does not currently point to
/// mapped, writable memory (in which case some data from before the
/// fault may be written), or `data` is larger than the user slice
/// (in which case no data is written).
pub fn write_all(self, data: &[u8]) -> Result {
self.writer().write_slice(data)
}
/// Constructs a [`UserSlicePtrWriter`].
pub fn writer(self) -> UserSlicePtrWriter {
UserSlicePtrWriter(self.0, self.1)
}
/// Constructs both a [`UserSlicePtrReader`] and a [`UserSlicePtrWriter`].
pub fn reader_writer(self) -> (UserSlicePtrReader, UserSlicePtrWriter) {
(
UserSlicePtrReader(self.0, self.1),
UserSlicePtrWriter(self.0, self.1),
)
}
}
/// A reader for [`UserSlicePtr`].
///
/// Used to incrementally read from the user slice.
pub struct UserSlicePtrReader(*mut core::ffi::c_void, usize);
impl IoBufferReader for UserSlicePtrReader {
/// Returns the number of bytes left to be read from this.
///
/// Note that even reading less than this number of bytes may fail.
fn len(&self) -> usize {
self.1
}
/// Reads raw data from the user slice into a raw kernel buffer.
///
/// # Safety
///
/// The output buffer must be valid.
unsafe fn read_raw(&mut self, out: *mut u8, len: usize) -> Result {
if len > self.1 || len > u32::MAX as usize {
return Err(EFAULT);
}
let res = unsafe { bindings::copy_from_user(out as _, self.0, len as _) };
if res != 0 {
return Err(EFAULT);
}
// Since this is not a pointer to a valid object in our program,
// we cannot use `add`, which has C-style rules for defined
// behavior.
self.0 = self.0.wrapping_add(len);
self.1 -= len;
Ok(())
}
}
/// A writer for [`UserSlicePtr`].
///
/// Used to incrementally write into the user slice.
pub struct UserSlicePtrWriter(*mut core::ffi::c_void, usize);
impl IoBufferWriter for UserSlicePtrWriter {
fn len(&self) -> usize {
self.1
}
fn clear(&mut self, mut len: usize) -> Result {
let mut ret = Ok(());
if len > self.1 {
ret = Err(EFAULT);
len = self.1;
}
// SAFETY: The buffer will be validated by `clear_user`. We ensure that `len` is within
// bounds in the check above.
let left = unsafe { bindings::clear_user(self.0, len as _) } as usize;
if left != 0 {
ret = Err(EFAULT);
len -= left;
}
self.0 = self.0.wrapping_add(len);
self.1 -= len;
ret
}
unsafe fn write_raw(&mut self, data: *const u8, len: usize) -> Result {
if len > self.1 || len > u32::MAX as usize {
return Err(EFAULT);
}
let res = unsafe { bindings::copy_to_user(self.0, data as _, len as _) };
if res != 0 {
return Err(EFAULT);
}
// Since this is not a pointer to a valid object in our program,
// we cannot use `add`, which has C-style rules for defined
// behavior.
self.0 = self.0.wrapping_add(len);
self.1 -= len;
Ok(())
}
}
|
