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
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
use crate::sealing;
use rustix::fs::{MemfdFlags, SealFlags};
use std::fs;
use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};

/// A `Memfd` builder, providing advanced options and flags for specifying its behavior.
#[derive(Clone, Debug)]
pub struct MemfdOptions {
    allow_sealing: bool,
    cloexec: bool,
    hugetlb: Option<HugetlbSize>,
}

impl MemfdOptions {
    /// Default set of options for `Memfd` creation.
    ///
    /// The default options are:
    ///  * [`FileSeal::SealSeal`] (i.e. no further sealing);
    ///  * close-on-exec is enabled;
    ///  * hugetlb is disabled.
    ///
    /// [`FileSeal::SealSeal`]: sealing::FileSeal::SealSeal
    pub const fn new() -> Self {
        Self {
            allow_sealing: false,
            cloexec: true,
            hugetlb: None,
        }
    }

    /// Whether to allow adding seals to the created `Memfd`.
    pub const fn allow_sealing(mut self, value: bool) -> Self {
        self.allow_sealing = value;
        self
    }

    /// Whether to set the `FD_CLOEXEC` flag on the created `Memfd`.
    pub const fn close_on_exec(mut self, value: bool) -> Self {
        self.cloexec = value;
        self
    }

    /// Optional hugetlb support and page size for the created `Memfd`.
    pub const fn hugetlb(mut self, size: Option<HugetlbSize>) -> Self {
        self.hugetlb = size;
        self
    }

    /// Translate the current options into a bitflags value for `memfd_create`.
    fn bitflags(&self) -> MemfdFlags {
        let mut bits = MemfdFlags::empty();
        if self.allow_sealing {
            bits |= MemfdFlags::ALLOW_SEALING;
        }
        if self.cloexec {
            bits |= MemfdFlags::CLOEXEC;
        }
        if let Some(ref hugetlb) = self.hugetlb {
            bits |= hugetlb.bitflags();
            bits |= MemfdFlags::HUGETLB;
        }
        bits
    }

    /// Create a [`Memfd`] according to configuration.
    ///
    /// [`Memfd`]: Memfd
    pub fn create<T: AsRef<str>>(&self, name: T) -> Result<Memfd, crate::Error> {
        let flags = self.bitflags();
        let fd = rustix::fs::memfd_create(name.as_ref(), flags)
            .map_err(Into::into)
            .map_err(crate::Error::Create)?;
        Ok(Memfd { file: fd.into() })
    }
}

impl Default for MemfdOptions {
    fn default() -> Self {
        Self::new()
    }
}

/// Page size for a hugetlb anonymous file.
#[derive(Copy, Clone, Debug)]
pub enum HugetlbSize {
    /// 64KB hugetlb page.
    Huge64KB,
    /// 64KB hugetlb page.
    Huge512KB,
    /// 1MB hugetlb page.
    Huge1MB,
    /// 2MB hugetlb page.
    Huge2MB,
    /// 8MB hugetlb page.
    Huge8MB,
    /// 16MB hugetlb page.
    Huge16MB,
    /// 256MB hugetlb page.
    Huge256MB,
    /// 1GB hugetlb page.
    Huge1GB,
    /// 2GB hugetlb page.
    Huge2GB,
    /// 16GB hugetlb page.
    Huge16GB,
}

impl HugetlbSize {
    const fn bitflags(self) -> MemfdFlags {
        match self {
            Self::Huge64KB => MemfdFlags::HUGE_64KB,
            Self::Huge512KB => MemfdFlags::HUGE_512KB,
            Self::Huge1MB => MemfdFlags::HUGE_1MB,
            Self::Huge2MB => MemfdFlags::HUGE_2MB,
            Self::Huge8MB => MemfdFlags::HUGE_8MB,
            Self::Huge16MB => MemfdFlags::HUGE_16MB,
            Self::Huge256MB => MemfdFlags::HUGE_256MB,
            Self::Huge1GB => MemfdFlags::HUGE_1GB,
            Self::Huge2GB => MemfdFlags::HUGE_2GB,
            Self::Huge16GB => MemfdFlags::HUGE_16GB,
        }
    }
}

/// An anonymous volatile file, with sealing capabilities.
#[derive(Debug)]
pub struct Memfd {
    file: fs::File,
}

impl Memfd {
    /// Try to convert an object that owns a file descriptor into a `Memfd`.
    ///
    /// This function consumes the ownership of the specified object. If the underlying
    /// file-descriptor is compatible with memfd/sealing, a `Memfd` object is returned.
    /// Otherwise the supplied object is returned as error.
    pub fn try_from_fd<F>(fd: F) -> Result<Self, F>
    where
        F: AsRawFd + IntoRawFd,
    {
        if is_memfd(&fd) {
            // SAFETY: from_raw_fd requires a valid, uniquely owned file descriptor.
            // The IntoRawFd trait guarantees both conditions.
            let file = unsafe { fs::File::from_raw_fd(fd.into_raw_fd()) };
            Ok(Self { file })
        } else {
            Err(fd)
        }
    }

    /// Try to convert a [`File`] object into a `Memfd`.
    ///
    /// This function consumes the ownership of the specified `File`.  If the underlying
    /// file-descriptor is compatible with memfd/sealing, a `Memfd` object is returned.
    /// Otherwise the supplied `File` is returned for further usage.
    ///
    /// [`File`]: fs::File
    pub fn try_from_file(file: fs::File) -> Result<Self, fs::File> {
        Self::try_from_fd(file)
    }

    /// Return a reference to the backing [`File`].
    ///
    /// [`File`]: fs::File
    pub const fn as_file(&self) -> &fs::File {
        &self.file
    }

    /// Convert `Memfd` to the backing [`File`].
    ///
    /// [`File`]: fs::File
    pub fn into_file(self) -> fs::File {
        self.file
    }

    /// Obtain the current set of seals for the `Memfd`.
    pub fn seals(&self) -> Result<sealing::SealsHashSet, crate::Error> {
        let flags = Self::file_get_seals(&self.file)?;
        Ok(sealing::bitflags_to_seals(flags))
    }

    /// Add a seal to the existing set of seals.
    pub fn add_seal(&self, seal: sealing::FileSeal) -> Result<(), crate::Error> {
        let flags = seal.bitflags();
        self.add_seal_flags(flags)
    }

    /// Add some seals to the existing set of seals.
    pub fn add_seals<'a>(
        &self,
        seals: impl IntoIterator<Item = &'a sealing::FileSeal>,
    ) -> Result<(), crate::Error> {
        let flags = sealing::seals_to_bitflags(seals);
        self.add_seal_flags(flags)
    }

    fn add_seal_flags(&self, flags: rustix::fs::SealFlags) -> Result<(), crate::Error> {
        rustix::fs::fcntl_add_seals(&self.file, flags)
            .map_err(Into::into)
            .map_err(crate::Error::AddSeals)?;
        Ok(())
    }

    /// Return the current sealing bitflags.
    fn file_get_seals(fp: &fs::File) -> Result<SealFlags, crate::Error> {
        let r = rustix::fs::fcntl_get_seals(fp)
            .map_err(Into::into)
            .map_err(crate::Error::GetSeals)?;
        Ok(r)
    }
}

impl FromRawFd for Memfd {
    /// Convert a raw file-descriptor to a [`Memfd`].
    ///
    /// This function consumes ownership of the specified file descriptor. `Memfd` will take
    /// responsibility for closing it when the object goes out of scope.
    ///
    /// # Safety
    ///
    /// `fd` must be a valid file descriptor representing a memfd file.
    ///
    /// [`Memfd`]: Memfd
    unsafe fn from_raw_fd(fd: RawFd) -> Self {
        let file = fs::File::from_raw_fd(fd);
        Self { file }
    }
}

impl AsRawFd for Memfd {
    fn as_raw_fd(&self) -> RawFd {
        self.file.as_raw_fd()
    }
}

impl IntoRawFd for Memfd {
    fn into_raw_fd(self) -> RawFd {
        self.into_file().into_raw_fd()
    }
}

/// Check if a file descriptor is a memfd.
///
/// Implemented by trying to retrieve the seals.
/// If that fails, the fd is not a memfd.
fn is_memfd<F: AsRawFd>(fd: &F) -> bool {
    // SAFETY: For now, we trust the file descriptor returned by `as_raw_fd()`
    // is valid. Once `AsFd` is stabilized in std, we can use that instead of
    // `AsRawFd`, and eliminate this `unsafe` block.
    let fd = unsafe { rustix::fd::BorrowedFd::borrow_raw(fd.as_raw_fd()) };
    rustix::fs::fcntl_get_seals(fd).is_ok()
}