This patchset contains some abstractions needed by the Rust
implementation of the Binder driver for passing data between userspace,
kernelspace, and directly into other processes.
These abstractions do not exactly match what was included in the Rust
Binder RFC - I have made various improvements and simplifications since
then. Nonetheless, please see the Rust Binder RFC [1] to get an
understanding for how this will be used:
Users of "rust: add userspace pointers"
and "rust: add typed accessors for userspace pointers":
rust_binder: add binderfs support to Rust binder
rust_binder: add threading support
rust_binder: add nodes and context managers
rust_binder: add oneway transactions
rust_binder: add death notifications
rust_binder: send nodes in transactions
rust_binder: add BINDER_TYPE_PTR support
rust_binder: add BINDER_TYPE_FDA support
rust_binder: add process freezing
Users of "rust: add abstraction for `struct page`":
rust_binder: add oneway transactions
rust_binder: add vma shrinker
Links: https://lore.kernel.org/rust-for-linux/[email protected]/ [1]
Signed-off-by: Alice Ryhl <[email protected]>
---
Changes in v6:
- Base on top of Wedson's Allocation APIs patchset.
- Do not define my own gfp flags, instead use the ones that are now
available in `kernel::alloc`.
- Add gfp flags to `read_all` methods instead of always using
GFP_KERNEL.
- The __GFP_HIGHMEM flag is not provided by the Allocation APIs
patchset, and I do not add it here. I will send a separate patchset
for adding it.
- Use usize instead of void pointer for userspace address.
- Add _raw suffix to `fill_zero` and `copy_from_user_slice`.
- Do not allow interior mutability in AsBytes/FromBytes.
- Doc changes:
- Mention that validity of user slices is checked at read/write time,
not in the constructor of the user slice.
- Mention that methods can also return EFAULT if a bounds check fails.
- Mention that methods may have partially copied data even if they
return EFAULT.
- Add link from `read_raw` to `read_slice`.
- Move comment about initialized memory on `read_raw` to
`# Guarantees` section.
- Add examples for `Page::alloc_page`.
- A previous version renamed UserSlicePtr to UserSlice but forgot to
update that in the commit message. Commit message fixed in this
version.
- Add Reviewed-by tags submitted on v5.
- Link to v5: https://lore.kernel.org/rust-for-linux/[email protected]/
Changes in v5:
- Fix casts in declarations of PAGE_* constants.
- Fix formatting of PAGE_MASK.
- Reformat comments at 100 line length.
- Minor fixes to safety comments of `read_raw` and `write_slice`.
- Link to v4: https://lore.kernel.org/rust-for-linux/[email protected]/
Changes in v4:
- Rephrase when we fail with EFAULT.
- Remove `pub` from examples.
- Use slices for raw uaccess methods.
- Fix PAGE_MASK constant.
- Rephrase most safety comments in Page abstraction.
- Make with_pointer_into_page and with_page_mapped private.
- Explain how raw pointers into pages are used correctly.
- Other minor doc improvements.
- Link to v3: https://lore.kernel.org/rust-for-linux/[email protected]/
Changes in v3:
- Fix bug in read_all.
- Add missing `#include <linux/nospec.h>`.
- Mention that the second patch passes CONFIG_TEST_USER_COPY.
- Add gfp flags for Page.
- Minor documentation adjustments.
- Link to v2: https://lore.kernel.org/rust-for-linux/[email protected]/
Changes in v2:
- Rename user_ptr module to uaccess.
- Use srctree-relative links.
- Improve documentation.
- Rename UserSlicePtr to UserSlice.
- Make read_to_end append to the buffer.
- Use named fields for uaccess types.
- Add examples.
- Use _copy_from/to_user to skip check_object_size.
- Rename traits and move to kernel::types.
- Remove PAGE_MASK constant.
- Rename page methods to say _raw.
- Link to v1: https://lore.kernel.org/rust-for-linux/[email protected]/
---
Alice Ryhl (2):
rust: uaccess: add typed accessors for userspace pointers
rust: add abstraction for `struct page`
Arnd Bergmann (1):
uaccess: always export _copy_[from|to]_user with CONFIG_RUST
Wedson Almeida Filho (1):
rust: uaccess: add userspace pointers
include/linux/uaccess.h | 38 ++--
lib/usercopy.c | 30 +---
rust/bindings/bindings_helper.h | 1 +
rust/helpers.c | 34 ++++
rust/kernel/alloc.rs | 7 +
rust/kernel/lib.rs | 2 +
rust/kernel/page.rs | 250 ++++++++++++++++++++++++++
rust/kernel/types.rs | 64 +++++++
rust/kernel/uaccess.rs | 388 ++++++++++++++++++++++++++++++++++++++++
9 files changed, 774 insertions(+), 40 deletions(-)
---
base-commit: 2c1092853f163762ef0aabc551a630ef233e1be3
change-id: 20231128-alice-mm-bc533456cee8
Best regards,
--
Alice Ryhl <[email protected]>
From: Wedson Almeida Filho <[email protected]>
A pointer to an area in userspace memory, which can be either read-only
or read-write.
All methods on this struct are safe: attempting to read or write on bad
addresses (either out of the bound of the slice or unmapped addresses)
will 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.
These APIs are designed to make it difficult to accidentally write
TOCTOU bugs. Every time you read from a memory location, the pointer is
advanced by the length so that you cannot use that reader to read the
same memory location twice. Preventing double-fetches avoids TOCTOU
bugs. This is accomplished by taking `self` by value to prevent
obtaining multiple readers on a given `UserSlice`, and the readers only
permitting forward reads. If double-fetching a memory location is
necessary for some reason, then that is done by creating multiple
readers to the same memory location.
Constructing a `UserSlice` 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).
This code is based on something that was originally written by Wedson on
the old rust branch. It was modified by Alice by removing the
`IoBufferReader` and `IoBufferWriter` traits, and various other changes.
Signed-off-by: Wedson Almeida Filho <[email protected]>
Co-developed-by: Alice Ryhl <[email protected]>
Reviewed-by: Benno Lossin <[email protected]>
Reviewed-by: Trevor Gross <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
---
rust/helpers.c | 14 +++
rust/kernel/lib.rs | 1 +
rust/kernel/uaccess.rs | 313 +++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 328 insertions(+)
diff --git a/rust/helpers.c b/rust/helpers.c
index 70e59efd92bc..312b6fcb49d5 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -38,6 +38,20 @@ __noreturn void rust_helper_BUG(void)
}
EXPORT_SYMBOL_GPL(rust_helper_BUG);
+unsigned long rust_helper_copy_from_user(void *to, const void __user *from,
+ unsigned long n)
+{
+ return copy_from_user(to, from, n);
+}
+EXPORT_SYMBOL_GPL(rust_helper_copy_from_user);
+
+unsigned long rust_helper_copy_to_user(void __user *to, const void *from,
+ unsigned long n)
+{
+ return copy_to_user(to, from, n);
+}
+EXPORT_SYMBOL_GPL(rust_helper_copy_to_user);
+
void rust_helper_mutex_lock(struct mutex *lock)
{
mutex_lock(lock);
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 9a943d99c71a..7ee807ae4680 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -45,6 +45,7 @@
pub mod task;
pub mod time;
pub mod types;
+pub mod uaccess;
pub mod workqueue;
#[doc(hidden)]
diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
new file mode 100644
index 000000000000..ee5623d7b98f
--- /dev/null
+++ b/rust/kernel/uaccess.rs
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Slices to user space memory regions.
+//!
+//! C header: [`include/linux/uaccess.h`](srctree/include/linux/uaccess.h)
+
+use crate::{alloc::Flags, bindings, error::Result, prelude::*};
+use alloc::vec::Vec;
+use core::ffi::{c_ulong, c_void};
+use core::mem::MaybeUninit;
+
+/// The type used for userspace addresses.
+pub type UserPtr = usize;
+
+/// A pointer to an area in userspace memory, which can be either read-only or read-write.
+///
+/// All methods on this struct are safe: attempting to read or write on bad addresses (either out of
+/// the bound of the slice or unmapped addresses) will 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.
+///
+/// These APIs are designed to make it difficult to accidentally write TOCTOU (time-of-check to
+/// time-of-use) bugs. Every time a memory location is read, the reader's position is advanced by
+/// the read length and the next read will start from there. This helps prevent accidentally reading
+/// the same location twice and causing a TOCTOU bug.
+///
+/// Creating a [`UserSliceReader`] and/or [`UserSliceWriter`] consumes the `UserSlice`, helping
+/// ensure that there aren't multiple readers or writers to the same location.
+///
+/// If double-fetching a memory location is necessary for some reason, then that is done by creating
+/// multiple readers to the same memory location, e.g. using [`clone_reader`].
+///
+/// # Examples
+///
+/// Takes a region of userspace memory from the current process, and modify it by adding one to
+/// every byte in the region.
+///
+/// ```no_run
+/// use alloc::vec::Vec;
+/// use core::ffi::c_void;
+/// use kernel::error::Result;
+/// use kernel::uaccess::{UserPtr, UserSlice};
+///
+/// fn bytes_add_one(uptr: UserPtr, len: usize) -> Result<()> {
+/// let (read, mut write) = UserSlice::new(uptr, len).reader_writer();
+///
+/// let mut buf = Vec::new();
+/// read.read_all(&mut buf, GFP_KERNEL)?;
+///
+/// for b in &mut buf {
+/// *b = b.wrapping_add(1);
+/// }
+///
+/// write.write_slice(&buf)?;
+/// Ok(())
+/// }
+/// ```
+///
+/// Example illustrating a TOCTOU (time-of-check to time-of-use) bug.
+///
+/// ```no_run
+/// use alloc::vec::Vec;
+/// use core::ffi::c_void;
+/// use kernel::error::{code::EINVAL, Result};
+/// use kernel::uaccess::{UserPtr, UserSlice};
+///
+/// /// Returns whether the data in this region is valid.
+/// fn is_valid(uptr: UserPtr, len: usize) -> Result<bool> {
+/// let read = UserSlice::new(uptr, len).reader();
+///
+/// let mut buf = Vec::new();
+/// read.read_all(&mut buf, GFP_KERNEL)?;
+///
+/// todo!()
+/// }
+///
+/// /// Returns the bytes behind this user pointer if they are valid.
+/// fn get_bytes_if_valid(uptr: UserPtr, len: usize) -> Result<Vec<u8>> {
+/// if !is_valid(uptr, len)? {
+/// return Err(EINVAL);
+/// }
+///
+/// let read = UserSlice::new(uptr, len).reader();
+///
+/// let mut buf = Vec::new();
+/// read.read_all(&mut buf, GFP_KERNEL)?;
+///
+/// // THIS IS A BUG! The bytes could have changed since we checked them.
+/// //
+/// // To avoid this kind of bug, don't call `UserSlice::new` multiple
+/// // times with the same address.
+/// Ok(buf)
+/// }
+/// ```
+///
+/// [`std::io`]: https://doc.rust-lang.org/std/io/index.html
+/// [`clone_reader`]: UserSliceReader::clone_reader
+pub struct UserSlice {
+ ptr: UserPtr,
+ length: usize,
+}
+
+impl UserSlice {
+ /// Constructs a user slice from a raw pointer and a length in bytes.
+ ///
+ /// Constructing a [`UserSlice`] 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). Validity of the pointer is checked when you
+ /// attempt to read or write, not in the call to `UserSlice::new`.
+ ///
+ /// Callers must be careful to avoid time-of-check-time-of-use (TOCTOU) issues. The simplest way
+ /// is to create a single instance of [`UserSlice`] per user memory block as it reads each byte
+ /// at most once.
+ pub fn new(ptr: UserPtr, length: usize) -> Self {
+ UserSlice { ptr, length }
+ }
+
+ /// Reads the entirety of the user slice, appending it to the end of the provided buffer.
+ ///
+ /// Fails with `EFAULT` if the read happens on a bad address.
+ pub fn read_all(self, buf: &mut Vec<u8>, flags: Flags) -> Result {
+ self.reader().read_all(buf, flags)
+ }
+
+ /// Constructs a [`UserSliceReader`].
+ pub fn reader(self) -> UserSliceReader {
+ UserSliceReader {
+ ptr: self.ptr,
+ length: self.length,
+ }
+ }
+
+ /// Constructs a [`UserSliceWriter`].
+ pub fn writer(self) -> UserSliceWriter {
+ UserSliceWriter {
+ ptr: self.ptr,
+ length: self.length,
+ }
+ }
+
+ /// Constructs both a [`UserSliceReader`] and a [`UserSliceWriter`].
+ ///
+ /// Usually when this is used, you will first read the data, and then overwrite it afterwards.
+ pub fn reader_writer(self) -> (UserSliceReader, UserSliceWriter) {
+ (
+ UserSliceReader {
+ ptr: self.ptr,
+ length: self.length,
+ },
+ UserSliceWriter {
+ ptr: self.ptr,
+ length: self.length,
+ },
+ )
+ }
+}
+
+/// A reader for [`UserSlice`].
+///
+/// Used to incrementally read from the user slice.
+pub struct UserSliceReader {
+ ptr: UserPtr,
+ length: usize,
+}
+
+impl UserSliceReader {
+ /// Skip the provided number of bytes.
+ ///
+ /// Returns an error if skipping more than the length of the buffer.
+ pub fn skip(&mut self, num_skip: usize) -> Result {
+ // Update `self.length` first since that's the fallible part of this operation.
+ self.length = self.length.checked_sub(num_skip).ok_or(EFAULT)?;
+ self.ptr = self.ptr.wrapping_add(num_skip);
+ Ok(())
+ }
+
+ /// Create a reader that can access the same range of data.
+ ///
+ /// Reading from the clone does not advance the current reader.
+ ///
+ /// The caller should take care to not introduce TOCTOU issues, as described in the
+ /// documentation for [`UserSlice`].
+ pub fn clone_reader(&self) -> UserSliceReader {
+ UserSliceReader {
+ ptr: self.ptr,
+ length: self.length,
+ }
+ }
+
+ /// Returns the number of bytes left to be read from this reader.
+ ///
+ /// Note that even reading less than this number of bytes may fail.
+ pub fn len(&self) -> usize {
+ self.length
+ }
+
+ /// Returns `true` if no data is available in the io buffer.
+ pub fn is_empty(&self) -> bool {
+ self.length == 0
+ }
+
+ /// Reads raw data from the user slice into a kernel buffer.
+ ///
+ /// For a version that uses `&mut [u8]`, please see [`UserSliceReader::read_slice`].
+ ///
+ /// Fails with `EFAULT` if the read happens on a bad address, or if the read goes out of bounds
+ /// of this [`UserSliceReader`]. This call may modify `out` even if it returns an error.
+ ///
+ /// # Guarantees
+ ///
+ /// After a successful call to this method, all bytes in `out` are initialized.
+ pub fn read_raw(&mut self, out: &mut [MaybeUninit<u8>]) -> Result {
+ let len = out.len();
+ let out_ptr = out.as_mut_ptr().cast::<c_void>();
+ if len > self.length {
+ return Err(EFAULT);
+ }
+ let Ok(len_ulong) = c_ulong::try_from(len) else {
+ return Err(EFAULT);
+ };
+ // SAFETY: `out_ptr` points into a mutable slice of length `len_ulong`, so we may write
+ // that many bytes to it.
+ let res =
+ unsafe { bindings::copy_from_user(out_ptr, self.ptr as *const c_void, len_ulong) };
+ if res != 0 {
+ return Err(EFAULT);
+ }
+ self.ptr = self.ptr.wrapping_add(len);
+ self.length -= len;
+ Ok(())
+ }
+
+ /// Reads raw data from the user slice into a kernel buffer.
+ ///
+ /// Fails with `EFAULT` if the read happens on a bad address, or if the read goes out of bounds
+ /// of this [`UserSliceReader`]. This call may modify `out` even if it returns an error.
+ pub fn read_slice(&mut self, out: &mut [u8]) -> Result {
+ // SAFETY: The types are compatible and `read_raw` doesn't write uninitialized bytes to
+ // `out`.
+ let out = unsafe { &mut *(out as *mut [u8] as *mut [MaybeUninit<u8>]) };
+ self.read_raw(out)
+ }
+
+ /// Reads the entirety of the user slice, appending it to the end of the provided buffer.
+ ///
+ /// Fails with `EFAULT` if the read happens on a bad address.
+ pub fn read_all(mut self, buf: &mut Vec<u8>, flags: Flags) -> Result {
+ let len = self.length;
+ buf.reserve(len, flags)?;
+
+ // The call to `try_reserve` was successful, so the spare capacity is at least `len` bytes
+ // long.
+ self.read_raw(&mut buf.spare_capacity_mut()[..len])?;
+
+ // SAFETY: Since the call to `read_raw` was successful, so the next `len` bytes of the
+ // vector have been initialized.
+ unsafe { buf.set_len(buf.len() + len) };
+ Ok(())
+ }
+}
+
+/// A writer for [`UserSlice`].
+///
+/// Used to incrementally write into the user slice.
+pub struct UserSliceWriter {
+ ptr: UserPtr,
+ length: usize,
+}
+
+impl UserSliceWriter {
+ /// Returns the amount of space remaining in this buffer.
+ ///
+ /// Note that even writing less than this number of bytes may fail.
+ pub fn len(&self) -> usize {
+ self.length
+ }
+
+ /// Returns `true` if no more data can be written to this buffer.
+ pub fn is_empty(&self) -> bool {
+ self.length == 0
+ }
+
+ /// Writes raw data to this user pointer from a kernel buffer.
+ ///
+ /// Fails with `EFAULT` if the write happens on a bad address, or if the write goes out of bounds
+ /// of this [`UserSliceWriter`]. This call may modify the associated userspace slice even if it
+ /// returns an error.
+ pub fn write_slice(&mut self, data: &[u8]) -> Result {
+ let len = data.len();
+ let data_ptr = data.as_ptr().cast::<c_void>();
+ if len > self.length {
+ return Err(EFAULT);
+ }
+ let Ok(len_ulong) = c_ulong::try_from(len) else {
+ return Err(EFAULT);
+ };
+ // SAFETY: `data_ptr` points into an immutable slice of length `len_ulong`, so we may read
+ // that many bytes from it.
+ let res = unsafe { bindings::copy_to_user(self.ptr as *mut c_void, data_ptr, len_ulong) };
+ if res != 0 {
+ return Err(EFAULT);
+ }
+ self.ptr = self.ptr.wrapping_add(len);
+ self.length -= len;
+ Ok(())
+ }
+}
--
2.44.0.683.g7961c838ac-goog
Add safe methods for reading and writing Rust values to and from
userspace pointers.
The C methods for copying to/from userspace use a function called
`check_object_size` to verify that the kernel pointer is not dangling.
However, this check is skipped when the length is a compile-time
constant, with the assumption that such cases trivially have a correct
kernel pointer.
In this patch, we apply the same optimization to the typed accessors.
For both methods, the size of the operation is known at compile time to
be size_of of the type being read or written. Since the C side doesn't
provide a variant that skips only this check, we create custom helpers
for this purpose.
The majority of reads and writes to userspace pointers in the Rust
Binder driver uses these accessor methods. Benchmarking has found that
skipping the `check_object_size` check makes a big difference for the
cases being skipped here. (And that the check doesn't make a difference
for the cases that use the raw read/write methods.)
This code is based on something that was originally written by Wedson on
the old rust branch. It was modified by Alice to skip the
`check_object_size` check, and to update various comments, including the
notes about kernel pointers in `WritableToBytes`.
Co-developed-by: Wedson Almeida Filho <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Benno Lossin <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Reviewed-by: Trevor Gross <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
---
rust/kernel/types.rs | 64 ++++++++++++++++++++++++++++++++++++++++
rust/kernel/uaccess.rs | 79 ++++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 141 insertions(+), 2 deletions(-)
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index 8fad61268465..9c57c6c75553 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -409,3 +409,67 @@ pub enum Either<L, R> {
/// Constructs an instance of [`Either`] containing a value of type `R`.
Right(R),
}
+
+/// Types for which any bit pattern is valid.
+///
+/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
+/// reading arbitrary bytes into something that contains a `bool` is not okay.
+///
+/// It's okay for the type to have padding, as initializing those bytes has no effect.
+///
+/// # Safety
+///
+/// All bit-patterns must be valid for this type. This type must not have interior mutability.
+pub unsafe trait FromBytes {}
+
+// SAFETY: All bit patterns are acceptable values of the types below.
+unsafe impl FromBytes for u8 {}
+unsafe impl FromBytes for u16 {}
+unsafe impl FromBytes for u32 {}
+unsafe impl FromBytes for u64 {}
+unsafe impl FromBytes for usize {}
+unsafe impl FromBytes for i8 {}
+unsafe impl FromBytes for i16 {}
+unsafe impl FromBytes for i32 {}
+unsafe impl FromBytes for i64 {}
+unsafe impl FromBytes for isize {}
+// SAFETY: If all bit patterns are acceptable for individual values in an array, then all bit
+// patterns are also acceptable for arrays of that type.
+unsafe impl<T: FromBytes> FromBytes for [T] {}
+unsafe impl<T: FromBytes, const N: usize> FromBytes for [T; N] {}
+
+/// Types that can be viewed as an immutable slice of initialized bytes.
+///
+/// If a struct implements this trait, then it is okay to copy it byte-for-byte to userspace. This
+/// means that it should not have any padding, as padding bytes are uninitialized. Reading
+/// uninitialized memory is not just undefined behavior, it may even lead to leaking sensitive
+/// information on the stack to userspace.
+///
+/// The struct should also not hold kernel pointers, as kernel pointer addresses are also considered
+/// sensitive. However, leaking kernel pointers is not considered undefined behavior by Rust, so
+/// this is a correctness requirement, but not a safety requirement.
+///
+/// # Safety
+///
+/// Values of this type may not contain any uninitialized bytes. This type must not have interior
+/// mutability.
+pub unsafe trait AsBytes {}
+
+// SAFETY: Instances of the following types have no uninitialized portions.
+unsafe impl AsBytes for u8 {}
+unsafe impl AsBytes for u16 {}
+unsafe impl AsBytes for u32 {}
+unsafe impl AsBytes for u64 {}
+unsafe impl AsBytes for usize {}
+unsafe impl AsBytes for i8 {}
+unsafe impl AsBytes for i16 {}
+unsafe impl AsBytes for i32 {}
+unsafe impl AsBytes for i64 {}
+unsafe impl AsBytes for isize {}
+unsafe impl AsBytes for bool {}
+unsafe impl AsBytes for char {}
+unsafe impl AsBytes for str {}
+// SAFETY: If individual values in an array have no uninitialized portions, then the array itself
+// does not have any uninitialized portions either.
+unsafe impl<T: AsBytes> AsBytes for [T] {}
+unsafe impl<T: AsBytes, const N: usize> AsBytes for [T; N] {}
diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
index ee5623d7b98f..39481e374c40 100644
--- a/rust/kernel/uaccess.rs
+++ b/rust/kernel/uaccess.rs
@@ -4,10 +4,16 @@
//!
//! C header: [`include/linux/uaccess.h`](srctree/include/linux/uaccess.h)
-use crate::{alloc::Flags, bindings, error::Result, prelude::*};
+use crate::{
+ alloc::Flags,
+ bindings,
+ error::Result,
+ prelude::*,
+ types::{AsBytes, FromBytes},
+};
use alloc::vec::Vec;
use core::ffi::{c_ulong, c_void};
-use core::mem::MaybeUninit;
+use core::mem::{size_of, MaybeUninit};
/// The type used for userspace addresses.
pub type UserPtr = usize;
@@ -247,6 +253,41 @@ pub fn read_slice(&mut self, out: &mut [u8]) -> Result {
self.read_raw(out)
}
+ /// Reads a value of the specified type.
+ ///
+ /// Fails with `EFAULT` if the read happens on a bad address, or if the read goes out of bounds
+ /// of this [`UserSliceReader`].
+ pub fn read<T: FromBytes>(&mut self) -> Result<T> {
+ let len = size_of::<T>();
+ if len > self.length {
+ return Err(EFAULT);
+ }
+ let Ok(len_ulong) = c_ulong::try_from(len) else {
+ return Err(EFAULT);
+ };
+ let mut out: MaybeUninit<T> = MaybeUninit::uninit();
+ // SAFETY: The local variable `out` is valid for writing `size_of::<T>()` bytes.
+ //
+ // By using the _copy_from_user variant, we skip the check_object_size check that verifies
+ // the kernel pointer. This mirrors the logic on the C side that skips the check when the
+ // length is a compile-time constant.
+ let res = unsafe {
+ bindings::_copy_from_user(
+ out.as_mut_ptr().cast::<c_void>(),
+ self.ptr as *const c_void,
+ len_ulong,
+ )
+ };
+ if res != 0 {
+ return Err(EFAULT);
+ }
+ self.ptr = self.ptr.wrapping_add(len);
+ self.length -= len;
+ // SAFETY: The read above has initialized all bytes in `out`, and since `T` implements
+ // `FromBytes`, any bit-pattern is a valid value for this type.
+ Ok(unsafe { out.assume_init() })
+ }
+
/// Reads the entirety of the user slice, appending it to the end of the provided buffer.
///
/// Fails with `EFAULT` if the read happens on a bad address.
@@ -310,4 +351,38 @@ pub fn write_slice(&mut self, data: &[u8]) -> Result {
self.length -= len;
Ok(())
}
+
+ /// Writes the provided Rust value to this userspace pointer.
+ ///
+ /// Fails with `EFAULT` if the write happens on a bad address, or if the write goes out of bounds
+ /// of this [`UserSliceWriter`]. This call may modify the associated userspace slice even if it
+ /// returns an error.
+ pub fn write<T: AsBytes>(&mut self, value: &T) -> Result {
+ let len = size_of::<T>();
+ if len > self.length {
+ return Err(EFAULT);
+ }
+ let Ok(len_ulong) = c_ulong::try_from(len) else {
+ return Err(EFAULT);
+ };
+ // SAFETY: The reference points to a value of type `T`, so it is valid for reading
+ // `size_of::<T>()` bytes.
+ //
+ // By using the _copy_to_user variant, we skip the check_object_size check that verifies the
+ // kernel pointer. This mirrors the logic on the C side that skips the check when the length
+ // is a compile-time constant.
+ let res = unsafe {
+ bindings::_copy_to_user(
+ self.ptr as *mut c_void,
+ (value as *const T).cast::<c_void>(),
+ len_ulong,
+ )
+ };
+ if res != 0 {
+ return Err(EFAULT);
+ }
+ self.ptr = self.ptr.wrapping_add(len);
+ self.length -= len;
+ Ok(())
+ }
}
--
2.44.0.683.g7961c838ac-goog
Adds a new struct called `Page` that wraps a pointer to `struct page`.
This struct is assumed to hold ownership over the page, so that Rust
code can allocate and manage pages directly.
The page type has various methods for reading and writing into the page.
These methods will temporarily map the page to allow the operation. All
of these methods use a helper that takes an offset and length, performs
bounds checks, and returns a pointer to the given offset in the page.
This patch only adds support for pages of order zero, as that is all
Rust Binder needs. However, it is written to make it easy to add support
for higher-order pages in the future. To do that, you would add a const
generic parameter to `Page` that specifies the order. Most of the
methods do not need to be adjusted, as the logic for dealing with
mapping multiple pages at once can be isolated to just the
`with_pointer_into_page` method.
Rust Binder needs to manage pages directly as that is how transactions
are delivered: Each process has an mmap'd region for incoming
transactions. When an incoming transaction arrives, the Binder driver
will choose a region in the mmap, allocate and map the relevant pages
manually, and copy the incoming transaction directly into the page. This
architecture allows the driver to copy transactions directly from the
address space of one process to another, without an intermediate copy
to a kernel buffer.
This code is based on Wedson's page abstractions from the old rust
branch, but it has been modified by Alice by removing the incomplete
support for higher-order pages, by introducing the `with_*` helpers
to consolidate the bounds checking logic into a single place, and
various other changes.
Co-developed-by: Wedson Almeida Filho <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Andreas Hindborg <[email protected]>
Reviewed-by: Trevor Gross <[email protected]>
Reviewed-by: Benno Lossin <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
---
rust/bindings/bindings_helper.h | 1 +
rust/helpers.c | 20 ++++
rust/kernel/alloc.rs | 7 ++
rust/kernel/lib.rs | 1 +
rust/kernel/page.rs | 250 ++++++++++++++++++++++++++++++++++++++++
5 files changed, 279 insertions(+)
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index ddb5644d4fd9..0862261cfbed 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -20,6 +20,7 @@
/* `bindgen` gets confused at certain things. */
const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;
+const size_t RUST_CONST_HELPER_PAGE_SIZE = PAGE_SIZE;
const gfp_t RUST_CONST_HELPER_GFP_ATOMIC = GFP_ATOMIC;
const gfp_t RUST_CONST_HELPER_GFP_KERNEL = GFP_KERNEL;
const gfp_t RUST_CONST_HELPER_GFP_KERNEL_ACCOUNT = GFP_KERNEL_ACCOUNT;
diff --git a/rust/helpers.c b/rust/helpers.c
index 312b6fcb49d5..72361003ba91 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -25,6 +25,8 @@
#include <linux/build_bug.h>
#include <linux/err.h>
#include <linux/errname.h>
+#include <linux/gfp.h>
+#include <linux/highmem.h>
#include <linux/mutex.h>
#include <linux/refcount.h>
#include <linux/sched/signal.h>
@@ -93,6 +95,24 @@ int rust_helper_signal_pending(struct task_struct *t)
}
EXPORT_SYMBOL_GPL(rust_helper_signal_pending);
+struct page *rust_helper_alloc_pages(gfp_t gfp_mask, unsigned int order)
+{
+ return alloc_pages(gfp_mask, order);
+}
+EXPORT_SYMBOL_GPL(rust_helper_alloc_pages);
+
+void *rust_helper_kmap_local_page(struct page *page)
+{
+ return kmap_local_page(page);
+}
+EXPORT_SYMBOL_GPL(rust_helper_kmap_local_page);
+
+void rust_helper_kunmap_local(const void *addr)
+{
+ kunmap_local(addr);
+}
+EXPORT_SYMBOL_GPL(rust_helper_kunmap_local);
+
refcount_t rust_helper_REFCOUNT_INIT(int n)
{
return (refcount_t)REFCOUNT_INIT(n);
diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs
index f1c2c4aa22d2..7ab2b33f19d4 100644
--- a/rust/kernel/alloc.rs
+++ b/rust/kernel/alloc.rs
@@ -20,6 +20,13 @@
#[derive(Clone, Copy)]
pub struct Flags(u32);
+impl Flags {
+ /// Get the raw representation of this flag.
+ pub(crate) fn as_raw(self) -> u32 {
+ self.0
+ }
+}
+
impl core::ops::BitOr for Flags {
type Output = Self;
fn bitor(self, rhs: Self) -> Self::Output {
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 7ee807ae4680..048e1662829a 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -35,6 +35,7 @@
pub mod kunit;
#[cfg(CONFIG_NET)]
pub mod net;
+pub mod page;
pub mod prelude;
pub mod print;
mod static_assert;
diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
new file mode 100644
index 000000000000..121d20066645
--- /dev/null
+++ b/rust/kernel/page.rs
@@ -0,0 +1,250 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Kernel page allocation and management.
+
+use crate::{
+ alloc::{AllocError, Flags},
+ bindings,
+ error::code::*,
+ error::Result,
+ uaccess::UserSliceReader,
+};
+use core::ptr::{self, NonNull};
+
+/// A bitwise shift for the page size.
+pub const PAGE_SHIFT: usize = bindings::PAGE_SHIFT as usize;
+
+/// The number of bytes in a page.
+pub const PAGE_SIZE: usize = bindings::PAGE_SIZE;
+
+/// A bitmask that gives the page containing a given address.
+pub const PAGE_MASK: usize = !(PAGE_SIZE - 1);
+
+/// A pointer to a page that owns the page allocation.
+///
+/// # Invariants
+///
+/// The pointer is valid, and has ownership over the page.
+pub struct Page {
+ page: NonNull<bindings::page>,
+}
+
+// SAFETY: Pages have no logic that relies on them staying on a given thread, so moving them across
+// threads is safe.
+unsafe impl Send for Page {}
+
+// SAFETY: Pages have no logic that relies on them not being accessed concurrently, so accessing
+// them concurrently is safe.
+unsafe impl Sync for Page {}
+
+impl Page {
+ /// Allocates a new page.
+ ///
+ /// # Examples
+ ///
+ /// Allocate memory for a page.
+ ///
+ /// ```
+ /// use kernel::page::Page;
+ ///
+ /// # fn dox() -> Result<(), kernel::alloc::AllocError> {
+ /// let page = Page::alloc_page(GFP_KERNEL)?;
+ /// # Ok(()) }
+ /// ```
+ ///
+ /// Allocate memory for a page and zero its contents.
+ ///
+ /// ```
+ /// use kernel::page::Page;
+ ///
+ /// # fn dox() -> Result<(), kernel::alloc::AllocError> {
+ /// let page = Page::alloc_page(GFP_KERNEL | __GFP_ZERO)?;
+ /// # Ok(()) }
+ /// ```
+ pub fn alloc_page(flags: Flags) -> Result<Self, AllocError> {
+ // SAFETY: Depending on the value of `gfp_flags`, this call may sleep. Other than that, it
+ // is always safe to call this method.
+ let page = unsafe { bindings::alloc_pages(flags.as_raw(), 0) };
+ let page = NonNull::new(page).ok_or(AllocError)?;
+ // INVARIANT: We just successfully allocated a page, so we now have ownership of the newly
+ // allocated page. We transfer that ownership to the new `Page` object.
+ Ok(Self { page })
+ }
+
+ /// Returns a raw pointer to the page.
+ pub fn as_ptr(&self) -> *mut bindings::page {
+ self.page.as_ptr()
+ }
+
+ /// Runs a piece of code with this page mapped to an address.
+ ///
+ /// The page is unmapped when this call returns.
+ ///
+ /// # Using the raw pointer
+ ///
+ /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
+ /// `PAGE_SIZE` bytes and for the duration in which the closure is called. The pointer might
+ /// only be mapped on the current thread, and when that is the case, dereferencing it on other
+ /// threads is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't
+ /// cause data races, the memory may be uninitialized, and so on.
+ ///
+ /// If multiple threads map the same page at the same time, then they may reference with
+ /// different addresses. However, even if the addresses are different, the underlying memory is
+ /// still the same for these purposes (e.g., it's still a data race if they both write to the
+ /// same underlying byte at the same time).
+ fn with_page_mapped<T>(&self, f: impl FnOnce(*mut u8) -> T) -> T {
+ // SAFETY: `page` is valid due to the type invariants on `Page`.
+ let mapped_addr = unsafe { bindings::kmap_local_page(self.as_ptr()) };
+
+ let res = f(mapped_addr.cast());
+
+ // This unmaps the page mapped above.
+ //
+ // SAFETY: Since this API takes the user code as a closure, it can only be used in a manner
+ // where the pages are unmapped in reverse order. This is as required by `kunmap_local`.
+ //
+ // In other words, if this call to `kunmap_local` happens when a different page should be
+ // unmapped first, then there must necessarily be a call to `kmap_local_page` other than the
+ // call just above in `with_page_mapped` that made that possible. In this case, it is the
+ // unsafe block that wraps that other call that is incorrect.
+ unsafe { bindings::kunmap_local(mapped_addr) };
+
+ res
+ }
+
+ /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
+ ///
+ /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
+ /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
+ /// this task, as this method uses a local mapping.
+ ///
+ /// If `off` and `len` refers to a region outside of this page, then this method returns
+ /// `EINVAL` and does not call `f`.
+ ///
+ /// # Using the raw pointer
+ ///
+ /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
+ /// `len` bytes and for the duration in which the closure is called. The pointer might only be
+ /// mapped on the current thread, and when that is the case, dereferencing it on other threads
+ /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
+ /// data races, the memory may be uninitialized, and so on.
+ ///
+ /// If multiple threads map the same page at the same time, then they may reference with
+ /// different addresses. However, even if the addresses are different, the underlying memory is
+ /// still the same for these purposes (e.g., it's still a data race if they both write to the
+ /// same underlying byte at the same time).
+ fn with_pointer_into_page<T>(
+ &self,
+ off: usize,
+ len: usize,
+ f: impl FnOnce(*mut u8) -> Result<T>,
+ ) -> Result<T> {
+ let bounds_ok = off <= PAGE_SIZE && len <= PAGE_SIZE && (off + len) <= PAGE_SIZE;
+
+ if bounds_ok {
+ self.with_page_mapped(move |page_addr| {
+ // SAFETY: The `off` integer is at most `PAGE_SIZE`, so this pointer offset will
+ // result in a pointer that is in bounds or one off the end of the page.
+ f(unsafe { page_addr.add(off) })
+ })
+ } else {
+ Err(EINVAL)
+ }
+ }
+
+ /// Maps the page and reads from it into the given buffer.
+ ///
+ /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes
+ /// outside ot the page, then this call returns `EINVAL`.
+ ///
+ /// # Safety
+ ///
+ /// * Callers must ensure that `dst` is valid for writing `len` bytes.
+ /// * Callers must ensure that this call does not race with a write to the same page that
+ /// overlaps with this read.
+ pub unsafe fn read_raw(&self, dst: *mut u8, offset: usize, len: usize) -> Result {
+ self.with_pointer_into_page(offset, len, move |src| {
+ // SAFETY: If `with_pointer_into_page` calls into this closure, then
+ // it has performed a bounds check and guarantees that `src` is
+ // valid for `len` bytes.
+ //
+ // There caller guarantees that there is no data race.
+ unsafe { ptr::copy_nonoverlapping(src, dst, len) };
+ Ok(())
+ })
+ }
+
+ /// Maps the page and writes into it from the given buffer.
+ ///
+ /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes
+ /// outside ot the page, then this call returns `EINVAL`.
+ ///
+ /// # Safety
+ ///
+ /// * Callers must ensure that `src` is valid for reading `len` bytes.
+ /// * Callers must ensure that this call does not race with a read or write to the same page
+ /// that overlaps with this write.
+ pub unsafe fn write_raw(&self, src: *const u8, offset: usize, len: usize) -> Result {
+ self.with_pointer_into_page(offset, len, move |dst| {
+ // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a
+ // bounds check and guarantees that `dst` is valid for `len` bytes.
+ //
+ // There caller guarantees that there is no data race.
+ unsafe { ptr::copy_nonoverlapping(src, dst, len) };
+ Ok(())
+ })
+ }
+
+ /// Maps the page and zeroes the given slice.
+ ///
+ /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes
+ /// outside ot the page, then this call returns `EINVAL`.
+ ///
+ /// # Safety
+ ///
+ /// Callers must ensure that this call does not race with a read or write to the same page that
+ /// overlaps with this write.
+ pub unsafe fn fill_zero_raw(&self, offset: usize, len: usize) -> Result {
+ self.with_pointer_into_page(offset, len, move |dst| {
+ // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a
+ // bounds check and guarantees that `dst` is valid for `len` bytes.
+ //
+ // There caller guarantees that there is no data race.
+ unsafe { ptr::write_bytes(dst, 0u8, len) };
+ Ok(())
+ })
+ }
+
+ /// Copies data from userspace into this page.
+ ///
+ /// This method will perform bounds checks on the page offset. If `offset .. offset+len` goes
+ /// outside ot the page, then this call returns `EINVAL`.
+ ///
+ /// Like the other `UserSliceReader` methods, data races are allowed on the userspace address.
+ /// However, they are not allowed on the page you are copying into.
+ ///
+ /// # Safety
+ ///
+ /// Callers must ensure that this call does not race with a read or write to the same page that
+ /// overlaps with this write.
+ pub unsafe fn copy_from_user_slice_raw(
+ &self,
+ reader: &mut UserSliceReader,
+ offset: usize,
+ len: usize,
+ ) -> Result {
+ self.with_pointer_into_page(offset, len, move |dst| {
+ // SAFETY: If `with_pointer_into_page` calls into this closure, then it has performed a
+ // bounds check and guarantees that `dst` is valid for `len` bytes. Furthermore, we have
+ // exclusive access to the slice since the caller guarantees that there are no races.
+ reader.read_raw(unsafe { core::slice::from_raw_parts_mut(dst.cast(), len) })
+ })
+ }
+}
+
+impl Drop for Page {
+ fn drop(&mut self) {
+ // SAFETY: By the type invariants, we have ownership of the page and can free it.
+ unsafe { bindings::__free_pages(self.page.as_ptr(), 0) };
+ }
+}
--
2.44.0.683.g7961c838ac-goog
From: Arnd Bergmann <[email protected]>
Rust code needs to be able to access _copy_from_user and _copy_to_user
so that it can skip the check_copy_size check in cases where the length
is known at compile-time, mirroring the logic for when C code will skip
check_copy_size. To do this, we ensure that exported versions of these
methods are available when CONFIG_RUST is enabled.
Alice has verified that this patch passes the CONFIG_TEST_USER_COPY test
on x86 using the Android cuttlefish emulator.
Signed-off-by: Arnd Bergmann <[email protected]>
Tested-by: Alice Ryhl <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
---
include/linux/uaccess.h | 38 ++++++++++++++++++++++++--------------
lib/usercopy.c | 30 ++++--------------------------
2 files changed, 28 insertions(+), 40 deletions(-)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 3064314f4832..2ebfce98b5cc 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -5,6 +5,7 @@
#include <linux/fault-inject-usercopy.h>
#include <linux/instrumented.h>
#include <linux/minmax.h>
+#include <linux/nospec.h>
#include <linux/sched.h>
#include <linux/thread_info.h>
@@ -138,13 +139,18 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
return raw_copy_to_user(to, from, n);
}
-#ifdef INLINE_COPY_FROM_USER
static inline __must_check unsigned long
-_copy_from_user(void *to, const void __user *from, unsigned long n)
+_inline_copy_from_user(void *to, const void __user *from, unsigned long n)
{
unsigned long res = n;
might_fault();
if (!should_fail_usercopy() && likely(access_ok(from, n))) {
+ /*
+ * Ensure that bad access_ok() speculation will not
+ * lead to nasty side effects *after* the copy is
+ * finished:
+ */
+ barrier_nospec();
instrument_copy_from_user_before(to, from, n);
res = raw_copy_from_user(to, from, n);
instrument_copy_from_user_after(to, from, n, res);
@@ -153,14 +159,11 @@ _copy_from_user(void *to, const void __user *from, unsigned long n)
memset(to + (n - res), 0, res);
return res;
}
-#else
extern __must_check unsigned long
_copy_from_user(void *, const void __user *, unsigned long);
-#endif
-#ifdef INLINE_COPY_TO_USER
static inline __must_check unsigned long
-_copy_to_user(void __user *to, const void *from, unsigned long n)
+_inline_copy_to_user(void __user *to, const void *from, unsigned long n)
{
might_fault();
if (should_fail_usercopy())
@@ -171,25 +174,32 @@ _copy_to_user(void __user *to, const void *from, unsigned long n)
}
return n;
}
-#else
extern __must_check unsigned long
_copy_to_user(void __user *, const void *, unsigned long);
-#endif
static __always_inline unsigned long __must_check
copy_from_user(void *to, const void __user *from, unsigned long n)
{
- if (check_copy_size(to, n, false))
- n = _copy_from_user(to, from, n);
- return n;
+ if (!check_copy_size(to, n, false))
+ return n;
+#ifdef INLINE_COPY_FROM_USER
+ return _inline_copy_from_user(to, from, n);
+#else
+ return _copy_from_user(to, from, n);
+#endif
}
static __always_inline unsigned long __must_check
copy_to_user(void __user *to, const void *from, unsigned long n)
{
- if (check_copy_size(from, n, true))
- n = _copy_to_user(to, from, n);
- return n;
+ if (!check_copy_size(from, n, true))
+ return n;
+
+#ifdef INLINE_COPY_TO_USER
+ return _inline_copy_to_user(to, from, n);
+#else
+ return _copy_to_user(to, from, n);
+#endif
}
#ifndef copy_mc_to_kernel
diff --git a/lib/usercopy.c b/lib/usercopy.c
index d29fe29c6849..de7f30618293 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -7,40 +7,18 @@
/* out-of-line parts */
-#ifndef INLINE_COPY_FROM_USER
+#if !defined(INLINE_COPY_FROM_USER) || defined(CONFIG_RUST)
unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
{
- unsigned long res = n;
- might_fault();
- if (!should_fail_usercopy() && likely(access_ok(from, n))) {
- /*
- * Ensure that bad access_ok() speculation will not
- * lead to nasty side effects *after* the copy is
- * finished:
- */
- barrier_nospec();
- instrument_copy_from_user_before(to, from, n);
- res = raw_copy_from_user(to, from, n);
- instrument_copy_from_user_after(to, from, n, res);
- }
- if (unlikely(res))
- memset(to + (n - res), 0, res);
- return res;
+ return _inline_copy_from_user(to, from, n);
}
EXPORT_SYMBOL(_copy_from_user);
#endif
-#ifndef INLINE_COPY_TO_USER
+#if !defined(INLINE_COPY_TO_USER) || defined(CONFIG_RUST)
unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
{
- might_fault();
- if (should_fail_usercopy())
- return n;
- if (likely(access_ok(to, n))) {
- instrument_copy_to_user(to, from, n);
- n = raw_copy_to_user(to, from, n);
- }
- return n;
+ return _inline_copy_to_user(to, from, n);
}
EXPORT_SYMBOL(_copy_to_user);
#endif
--
2.44.0.683.g7961c838ac-goog
On 18.04.24 10:59, Alice Ryhl wrote:
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 8fad61268465..9c57c6c75553 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -409,3 +409,67 @@ pub enum Either<L, R> {
> /// Constructs an instance of [`Either`] containing a value of type `R`.
> Right(R),
> }
> +
> +/// Types for which any bit pattern is valid.
> +///
> +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
> +/// reading arbitrary bytes into something that contains a `bool` is not okay.
> +///
> +/// It's okay for the type to have padding, as initializing those bytes has no effect.
> +///
> +/// # Safety
> +///
> +/// All bit-patterns must be valid for this type. This type must not have interior mutability.
What is the reason for disallowing interior mutability here? I agree
that it is necessary for `AsBytes`, but I don't think we need it here.
For example it is fine to convert `u8` to `UnsafeCell<u8>`. Niches also
should not be a problem, since eg `Option<UnsafeCell<NonNull<u8>>>`
already fails the "All bit-patterns must be valid for this type".
--
Cheers,
Benno
> +pub unsafe trait FromBytes {}
> +
> +// SAFETY: All bit patterns are acceptable values of the types below.
> +unsafe impl FromBytes for u8 {}
> +unsafe impl FromBytes for u16 {}
> +unsafe impl FromBytes for u32 {}
> +unsafe impl FromBytes for u64 {}
> +unsafe impl FromBytes for usize {}
> +unsafe impl FromBytes for i8 {}
> +unsafe impl FromBytes for i16 {}
> +unsafe impl FromBytes for i32 {}
> +unsafe impl FromBytes for i64 {}
> +unsafe impl FromBytes for isize {}
On Thu, Apr 18, 2024 at 3:02 PM Benno Lossin <[email protected]> wrote:
>
> On 18.04.24 10:59, Alice Ryhl wrote:
> > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> > index 8fad61268465..9c57c6c75553 100644
> > --- a/rust/kernel/types.rs
> > +++ b/rust/kernel/types.rs
> > @@ -409,3 +409,67 @@ pub enum Either<L, R> {
> > /// Constructs an instance of [`Either`] containing a value of type `R`.
> > Right(R),
> > }
> > +
> > +/// Types for which any bit pattern is valid.
> > +///
> > +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
> > +/// reading arbitrary bytes into something that contains a `bool` is not okay.
> > +///
> > +/// It's okay for the type to have padding, as initializing those bytes has no effect.
> > +///
> > +/// # Safety
> > +///
> > +/// All bit-patterns must be valid for this type. This type must not have interior mutability.
>
> What is the reason for disallowing interior mutability here? I agree
> that it is necessary for `AsBytes`, but I don't think we need it here.
> For example it is fine to convert `u8` to `UnsafeCell<u8>`. Niches also
> should not be a problem, since eg `Option<UnsafeCell<NonNull<u8>>>`
> already fails the "All bit-patterns must be valid for this type".
If T: FromBytes allows transmuting &[u8; size_of::<T>] into &T, then
it would be a problem as you could then use it to modify the original
&[u8].
Alice
On Thu, Apr 18, 2024 at 04:23:06PM +0000, Benno Lossin wrote:
> On 18.04.24 15:17, Alice Ryhl wrote:
> > On Thu, Apr 18, 2024 at 3:02 PM Benno Lossin <[email protected]> wrote:
> >>
> >> On 18.04.24 10:59, Alice Ryhl wrote:
> >>> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> >>> index 8fad61268465..9c57c6c75553 100644
> >>> --- a/rust/kernel/types.rs
> >>> +++ b/rust/kernel/types.rs
> >>> @@ -409,3 +409,67 @@ pub enum Either<L, R> {
> >>> /// Constructs an instance of [`Either`] containing a value of type `R`.
> >>> Right(R),
> >>> }
> >>> +
> >>> +/// Types for which any bit pattern is valid.
> >>> +///
> >>> +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
> >>> +/// reading arbitrary bytes into something that contains a `bool` is not okay.
> >>> +///
> >>> +/// It's okay for the type to have padding, as initializing those bytes has no effect.
> >>> +///
> >>> +/// # Safety
> >>> +///
> >>> +/// All bit-patterns must be valid for this type. This type must not have interior mutability.
> >>
> >> What is the reason for disallowing interior mutability here? I agree
> >> that it is necessary for `AsBytes`, but I don't think we need it here.
Hmm.. technically, if the interior mutability behaves in a way that each
byte is still initialized during the modification, then it should be
fine for `AsBytes`, for example and `AtomicI32` (implemented by asm
blocks)? Not making any change suggestion, just checking my understand.
Regards,
Boqun
> >> For example it is fine to convert `u8` to `UnsafeCell<u8>`. Niches also
> >> should not be a problem, since eg `Option<UnsafeCell<NonNull<u8>>>`
> >> already fails the "All bit-patterns must be valid for this type".
> >
> > If T: FromBytes allows transmuting &[u8; size_of::<T>] into &T, then
> > it would be a problem as you could then use it to modify the original
> > &[u8].
>
> Ahh that makes a lot of sense.
>
> --
> Cheers,
> Benno
>
>
On Thu, Apr 18, 2024 at 9:03 AM Benno Lossin <[email protected]> wrote:
>
> On 18.04.24 10:59, Alice Ryhl wrote:
> > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> > index 8fad61268465..9c57c6c75553 100644
> > --- a/rust/kernel/types.rs
> > +++ b/rust/kernel/types.rs
> > @@ -409,3 +409,67 @@ pub enum Either<L, R> {
> > /// Constructs an instance of [`Either`] containing a value of type `R`.
> > Right(R),
> > }
> > +
> > +/// Types for which any bit pattern is valid.
> > +///
> > +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
> > +/// reading arbitrary bytes into something that contains a `bool` is not okay.
> > +///
> > +/// It's okay for the type to have padding, as initializing those bytes has no effect.
> > +///
> > +/// # Safety
> > +///
> > +/// All bit-patterns must be valid for this type. This type must not have interior mutability.
>
> What is the reason for disallowing interior mutability here? I agree
> that it is necessary for `AsBytes`, but I don't think we need it here.
> For example it is fine to convert `u8` to `UnsafeCell<u8>`. Niches also
> should not be a problem, since eg `Option<UnsafeCell<NonNull<u8>>>`
> already fails the "All bit-patterns must be valid for this type".
>
> --
> Cheers,
> Benno
>
> > +pub unsafe trait FromBytes {}
See also the reasoning in zerocopy [1] and bytemuck [2]
[1]: https://docs.rs/zerocopy/latest/zerocopy/derive.FromBytes.html#analysis
[2]: https://docs.rs/bytemuck/latest/bytemuck/trait.AnyBitPattern.html#safety
On Thu, Apr 18, 2024 at 08:59:20AM +0000, Alice Ryhl wrote:
> Adds a new struct called `Page` that wraps a pointer to `struct page`.
> This struct is assumed to hold ownership over the page, so that Rust
> code can allocate and manage pages directly.
>
> The page type has various methods for reading and writing into the page.
> These methods will temporarily map the page to allow the operation. All
> of these methods use a helper that takes an offset and length, performs
> bounds checks, and returns a pointer to the given offset in the page.
>
> This patch only adds support for pages of order zero, as that is all
> Rust Binder needs. However, it is written to make it easy to add support
> for higher-order pages in the future. To do that, you would add a const
> generic parameter to `Page` that specifies the order. Most of the
> methods do not need to be adjusted, as the logic for dealing with
> mapping multiple pages at once can be isolated to just the
> `with_pointer_into_page` method.
>
Thank you for doing this, and breaking the chicken-and-egg problem chain
;-) For sure, the whole package of page API would need more time to
design, implement and review, but this patch looks good enough to me.
> Rust Binder needs to manage pages directly as that is how transactions
> are delivered: Each process has an mmap'd region for incoming
> transactions. When an incoming transaction arrives, the Binder driver
> will choose a region in the mmap, allocate and map the relevant pages
> manually, and copy the incoming transaction directly into the page. This
> architecture allows the driver to copy transactions directly from the
> address space of one process to another, without an intermediate copy
> to a kernel buffer.
>
> This code is based on Wedson's page abstractions from the old rust
> branch, but it has been modified by Alice by removing the incomplete
> support for higher-order pages, by introducing the `with_*` helpers
> to consolidate the bounds checking logic into a single place, and
> various other changes.
>
> Co-developed-by: Wedson Almeida Filho <[email protected]>
> Signed-off-by: Wedson Almeida Filho <[email protected]>
> Reviewed-by: Andreas Hindborg <[email protected]>
> Reviewed-by: Trevor Gross <[email protected]>
> Reviewed-by: Benno Lossin <[email protected]>
> Signed-off-by: Alice Ryhl <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Something I want to bring up for discussion below:
[...]
> + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
> + ///
> + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
> + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
> + /// this task, as this method uses a local mapping.
> + ///
> + /// If `off` and `len` refers to a region outside of this page, then this method returns
> + /// `EINVAL` and does not call `f`.
> + ///
> + /// # Using the raw pointer
> + ///
> + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
> + /// `len` bytes and for the duration in which the closure is called. The pointer might only be
> + /// mapped on the current thread, and when that is the case, dereferencing it on other threads
> + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
> + /// data races, the memory may be uninitialized, and so on.
> + ///
> + /// If multiple threads map the same page at the same time, then they may reference with
> + /// different addresses. However, even if the addresses are different, the underlying memory is
> + /// still the same for these purposes (e.g., it's still a data race if they both write to the
> + /// same underlying byte at the same time).
> + fn with_pointer_into_page<T>(
> + &self,
> + off: usize,
> + len: usize,
> + f: impl FnOnce(*mut u8) -> Result<T>,
I wonder whether the way to go here is making this function signature:
fn with_slice_in_page<T> (
&self,
off: usize,
len: usize,
f: iml FnOnce(&UnsafeCell<[u8]>) -> Result<T>
) -> Result<T>
, because in this way, it makes a bit more clear that what memory that
`f` can access, in other words, the users are less likely to use the
pointer in a wrong way.
But that depends on whether `&UnsafeCell<[u8]>` is the correct
abstraction and the ecosystem around it: for example, I feel like these
two functions:
fn len(slice: &UnsafeCell<[u8]>) -> usize
fn as_ptr(slice: &UnsafeCell<[u8]>) -> *mut u8
should be trivially safe, but I might be wrong. Again this is just for
future discussion.
Regards,
Boqun
> + ) -> Result<T> {
> + let bounds_ok = off <= PAGE_SIZE && len <= PAGE_SIZE && (off + len) <= PAGE_SIZE;
> +
> + if bounds_ok {
> + self.with_page_mapped(move |page_addr| {
> + // SAFETY: The `off` integer is at most `PAGE_SIZE`, so this pointer offset will
> + // result in a pointer that is in bounds or one off the end of the page.
> + f(unsafe { page_addr.add(off) })
> + })
> + } else {
> + Err(EINVAL)
> + }
> + }
> +
[...]
>
> --
> 2.44.0.683.g7961c838ac-goog
>
On Thu, Apr 18, 2024 at 7:27 PM Boqun Feng <[email protected]> wrote:
>
> On Thu, Apr 18, 2024 at 04:23:06PM +0000, Benno Lossin wrote:
> > On 18.04.24 15:17, Alice Ryhl wrote:
> > > On Thu, Apr 18, 2024 at 3:02 PM Benno Lossin <[email protected]> wrote:
> > >>
> > >> On 18.04.24 10:59, Alice Ryhl wrote:
> > >>> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> > >>> index 8fad61268465..9c57c6c75553 100644
> > >>> --- a/rust/kernel/types.rs
> > >>> +++ b/rust/kernel/types.rs
> > >>> @@ -409,3 +409,67 @@ pub enum Either<L, R> {
> > >>> /// Constructs an instance of [`Either`] containing a value of type `R`.
> > >>> Right(R),
> > >>> }
> > >>> +
> > >>> +/// Types for which any bit pattern is valid.
> > >>> +///
> > >>> +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
> > >>> +/// reading arbitrary bytes into something that contains a `bool` is not okay.
> > >>> +///
> > >>> +/// It's okay for the type to have padding, as initializing those bytes has no effect.
> > >>> +///
> > >>> +/// # Safety
> > >>> +///
> > >>> +/// All bit-patterns must be valid for this type. This type must not have interior mutability.
> > >>
> > >> What is the reason for disallowing interior mutability here? I agree
> > >> that it is necessary for `AsBytes`, but I don't think we need it here.
>
> Hmm.. technically, if the interior mutability behaves in a way that each
> byte is still initialized during the modification, then it should be
> fine for `AsBytes`, for example and `AtomicI32` (implemented by asm
> blocks)? Not making any change suggestion, just checking my understand.
No, that's UB. When the type is not interior mutable, then any two
loads from the same immutable reference may be assumed to return the
same value. Changing it with an atomic would violate that since the
value changes.
Alice
On Thu, Apr 18, 2024 at 09:35:53PM +0200, Alice Ryhl wrote:
> On Thu, Apr 18, 2024 at 7:27 PM Boqun Feng <[email protected]> wrote:
> >
> > On Thu, Apr 18, 2024 at 04:23:06PM +0000, Benno Lossin wrote:
> > > On 18.04.24 15:17, Alice Ryhl wrote:
> > > > On Thu, Apr 18, 2024 at 3:02 PM Benno Lossin <[email protected]> wrote:
> > > >>
> > > >> On 18.04.24 10:59, Alice Ryhl wrote:
> > > >>> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> > > >>> index 8fad61268465..9c57c6c75553 100644
> > > >>> --- a/rust/kernel/types.rs
> > > >>> +++ b/rust/kernel/types.rs
> > > >>> @@ -409,3 +409,67 @@ pub enum Either<L, R> {
> > > >>> /// Constructs an instance of [`Either`] containing a value of type `R`.
> > > >>> Right(R),
> > > >>> }
> > > >>> +
> > > >>> +/// Types for which any bit pattern is valid.
> > > >>> +///
> > > >>> +/// Not all types are valid for all values. For example, a `bool` must be either zero or one, so
> > > >>> +/// reading arbitrary bytes into something that contains a `bool` is not okay.
> > > >>> +///
> > > >>> +/// It's okay for the type to have padding, as initializing those bytes has no effect.
> > > >>> +///
> > > >>> +/// # Safety
> > > >>> +///
> > > >>> +/// All bit-patterns must be valid for this type. This type must not have interior mutability.
> > > >>
> > > >> What is the reason for disallowing interior mutability here? I agree
> > > >> that it is necessary for `AsBytes`, but I don't think we need it here.
> >
> > Hmm.. technically, if the interior mutability behaves in a way that each
> > byte is still initialized during the modification, then it should be
> > fine for `AsBytes`, for example and `AtomicI32` (implemented by asm
> > blocks)? Not making any change suggestion, just checking my understand.
>
> No, that's UB. When the type is not interior mutable, then any two
> loads from the same immutable reference may be assumed to return the
> same value. Changing it with an atomic would violate that since the
> value changes.
>
Oh, that makes sense! Thanks!
Regards,
Boqun
> Alice
On Thu, Apr 18, 2024 at 10:08:40PM +0000, Benno Lossin wrote:
> On 18.04.24 20:52, Boqun Feng wrote:
> > On Thu, Apr 18, 2024 at 08:59:20AM +0000, Alice Ryhl wrote:
> >> + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
> >> + ///
> >> + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
> >> + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
> >> + /// this task, as this method uses a local mapping.
> >> + ///
> >> + /// If `off` and `len` refers to a region outside of this page, then this method returns
> >> + /// `EINVAL` and does not call `f`.
> >> + ///
> >> + /// # Using the raw pointer
> >> + ///
> >> + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
> >> + /// `len` bytes and for the duration in which the closure is called. The pointer might only be
> >> + /// mapped on the current thread, and when that is the case, dereferencing it on other threads
> >> + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
> >> + /// data races, the memory may be uninitialized, and so on.
> >> + ///
> >> + /// If multiple threads map the same page at the same time, then they may reference with
> >> + /// different addresses. However, even if the addresses are different, the underlying memory is
> >> + /// still the same for these purposes (e.g., it's still a data race if they both write to the
> >> + /// same underlying byte at the same time).
> >> + fn with_pointer_into_page<T>(
> >> + &self,
> >> + off: usize,
> >> + len: usize,
> >> + f: impl FnOnce(*mut u8) -> Result<T>,
> >
> > I wonder whether the way to go here is making this function signature:
> >
> > fn with_slice_in_page<T> (
> > &self,
> > off: usize,
> > len: usize,
> > f: iml FnOnce(&UnsafeCell<[u8]>) -> Result<T>
> > ) -> Result<T>
> >
> > , because in this way, it makes a bit more clear that what memory that
> > `f` can access, in other words, the users are less likely to use the
> > pointer in a wrong way.
> >
> > But that depends on whether `&UnsafeCell<[u8]>` is the correct
> > abstraction and the ecosystem around it: for example, I feel like these
> > two functions:
> >
> > fn len(slice: &UnsafeCell<[u8]>) -> usize
> > fn as_ptr(slice: &UnsafeCell<[u8]>) -> *mut u8
> >
> > should be trivially safe, but I might be wrong. Again this is just for
> > future discussion.
>
> I think the "better" type would be `&[UnsafeCell<u8>]`. Since there you
> can always access the length.
>
Hmm.. here is the thing, having `&UnsafeCell<[u8]>` means having a `*mut
[u8]>`, and it should always be safe to get a "length" of `*mut [u8]`,
right? I haven't found any method doing that, but the length should be
just a part of fat pointer, so I think getting that is a defined
behavior. But maybe I'm missing something.
> Another question would be if page allows for uninitialized bits, in that
> case, we would need `&[Opaque<u8>]`.
>
Yes, or `&Opaque<[u8>]`.
Regards,
Boqun
> But I don't remember how to get a valid raw pointer from
> `&[UnsafeCell<u8>]`.
>
> --
> Cheers,
> Benno
>
On Thu, Apr 18, 2024 at 03:56:11PM -0700, Boqun Feng wrote:
> On Thu, Apr 18, 2024 at 10:08:40PM +0000, Benno Lossin wrote:
> > On 18.04.24 20:52, Boqun Feng wrote:
> > > On Thu, Apr 18, 2024 at 08:59:20AM +0000, Alice Ryhl wrote:
> > >> + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
> > >> + ///
> > >> + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
> > >> + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
> > >> + /// this task, as this method uses a local mapping.
> > >> + ///
> > >> + /// If `off` and `len` refers to a region outside of this page, then this method returns
> > >> + /// `EINVAL` and does not call `f`.
> > >> + ///
> > >> + /// # Using the raw pointer
> > >> + ///
> > >> + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
> > >> + /// `len` bytes and for the duration in which the closure is called. The pointer might only be
> > >> + /// mapped on the current thread, and when that is the case, dereferencing it on other threads
> > >> + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
> > >> + /// data races, the memory may be uninitialized, and so on.
> > >> + ///
> > >> + /// If multiple threads map the same page at the same time, then they may reference with
> > >> + /// different addresses. However, even if the addresses are different, the underlying memory is
> > >> + /// still the same for these purposes (e.g., it's still a data race if they both write to the
> > >> + /// same underlying byte at the same time).
> > >> + fn with_pointer_into_page<T>(
> > >> + &self,
> > >> + off: usize,
> > >> + len: usize,
> > >> + f: impl FnOnce(*mut u8) -> Result<T>,
> > >
> > > I wonder whether the way to go here is making this function signature:
> > >
> > > fn with_slice_in_page<T> (
> > > &self,
> > > off: usize,
> > > len: usize,
> > > f: iml FnOnce(&UnsafeCell<[u8]>) -> Result<T>
> > > ) -> Result<T>
> > >
> > > , because in this way, it makes a bit more clear that what memory that
> > > `f` can access, in other words, the users are less likely to use the
> > > pointer in a wrong way.
> > >
> > > But that depends on whether `&UnsafeCell<[u8]>` is the correct
> > > abstraction and the ecosystem around it: for example, I feel like these
> > > two functions:
> > >
> > > fn len(slice: &UnsafeCell<[u8]>) -> usize
> > > fn as_ptr(slice: &UnsafeCell<[u8]>) -> *mut u8
> > >
> > > should be trivially safe, but I might be wrong. Again this is just for
> > > future discussion.
> >
> > I think the "better" type would be `&[UnsafeCell<u8>]`. Since there you
> > can always access the length.
> >
>
> Hmm.. here is the thing, having `&UnsafeCell<[u8]>` means having a `*mut
> [u8]>`, and it should always be safe to get a "length" of `*mut [u8]`,
> right? I haven't found any method doing that, but the length should be
> just a part of fat pointer, so I think getting that is a defined
> behavior. But maybe I'm missing something.
>
Hmm... but I guess one of the problems of this approach, is how to
construct a `&UnsafeCell<[u8]>` from a pointer and length...
Regards,
Boqun
> > Another question would be if page allows for uninitialized bits, in that
> > case, we would need `&[Opaque<u8>]`.
> >
>
> Yes, or `&Opaque<[u8>]`.
>
> Regards,
> Boqun
>
> > But I don't remember how to get a valid raw pointer from
> > `&[UnsafeCell<u8>]`.
> >
> > --
> > Cheers,
> > Benno
> >
On Thu, Apr 18, 2024 at 08:59:17AM +0000, Alice Ryhl wrote:
[...]
> + /// Reads the entirety of the user slice, appending it to the end of the provided buffer.
> + ///
> + /// Fails with `EFAULT` if the read happens on a bad address.
> + pub fn read_all(mut self, buf: &mut Vec<u8>, flags: Flags) -> Result {
> + let len = self.length;
> + buf.reserve(len, flags)?;
(Reportedy by Miguel)
When compile with `make rusttest`, kernel crate is compiled as userspace
program, so we need to explicitly pick where the `reserve` comes from
(Vec or VecExt), the current version will hit the following error:
error[E0061]: this method takes 1 argument but 2 arguments were supplied
--> rust/kernel/uaccess.rs:296:13
|
296 | buf.reserve(len, flags)?;
| ^^^^^^^ -------
| | |
| | unexpected argument of type `Flags`
| help: remove the extra argument
|
note: method defined here
--> /home/boqun/linux-rust/rust/test/sysroot/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:910:12
|
910 | pub fn reserve(&mut self, additional: usize) {
| ^^^^^^^
error[E0277]: the `?` operator can only be applied to values that implement `Try`
--> rust/kernel/uaccess.rs:296:9
|
296 | buf.reserve(len, flags)?;
| ^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `()`
|
= help: the trait `Try` is not implemented for `()`
error: aborting due to 2 previous errors
Some errors have detailed explanations: E0061, E0277.
For more information about an error, try `rustc --explain E0061`.
and we need to the following fix
diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
index 39481e374c40..80f7e7ca2f5e 100644
--- a/rust/kernel/uaccess.rs
+++ b/rust/kernel/uaccess.rs
@@ -293,7 +293,7 @@ pub fn read<T: FromBytes>(&mut self) -> Result<T> {
/// Fails with `EFAULT` if the read happens on a bad address.
pub fn read_all(mut self, buf: &mut Vec<u8>, flags: Flags) -> Result {
let len = self.length;
- buf.reserve(len, flags)?;
+ VecExt::<u8>::reserve(buf, len, flags)?;
// The call to `try_reserve` was successful, so the spare capacity is at least `len` bytes
// long.
Regards,
Boqun
> +
> + // The call to `try_reserve` was successful, so the spare capacity is at least `len` bytes
> + // long.
> + self.read_raw(&mut buf.spare_capacity_mut()[..len])?;
> +
> + // SAFETY: Since the call to `read_raw` was successful, so the next `len` bytes of the
> + // vector have been initialized.
> + unsafe { buf.set_len(buf.len() + len) };
> + Ok(())
> + }
> +}
> +
> +/// A writer for [`UserSlice`].
> +///
> +/// Used to incrementally write into the user slice.
> +pub struct UserSliceWriter {
> + ptr: UserPtr,
> + length: usize,
> +}
> +
> +impl UserSliceWriter {
> + /// Returns the amount of space remaining in this buffer.
> + ///
> + /// Note that even writing less than this number of bytes may fail.
> + pub fn len(&self) -> usize {
> + self.length
> + }
> +
> + /// Returns `true` if no more data can be written to this buffer.
> + pub fn is_empty(&self) -> bool {
> + self.length == 0
> + }
> +
> + /// Writes raw data to this user pointer from a kernel buffer.
> + ///
> + /// Fails with `EFAULT` if the write happens on a bad address, or if the write goes out of bounds
> + /// of this [`UserSliceWriter`]. This call may modify the associated userspace slice even if it
> + /// returns an error.
> + pub fn write_slice(&mut self, data: &[u8]) -> Result {
> + let len = data.len();
> + let data_ptr = data.as_ptr().cast::<c_void>();
> + if len > self.length {
> + return Err(EFAULT);
> + }
> + let Ok(len_ulong) = c_ulong::try_from(len) else {
> + return Err(EFAULT);
> + };
> + // SAFETY: `data_ptr` points into an immutable slice of length `len_ulong`, so we may read
> + // that many bytes from it.
> + let res = unsafe { bindings::copy_to_user(self.ptr as *mut c_void, data_ptr, len_ulong) };
> + if res != 0 {
> + return Err(EFAULT);
> + }
> + self.ptr = self.ptr.wrapping_add(len);
> + self.length -= len;
> + Ok(())
> + }
> +}
>
> --
> 2.44.0.683.g7961c838ac-goog
>
On Fri, Apr 19, 2024 at 08:36:11AM +0000, Benno Lossin wrote:
> On 19.04.24 01:04, Boqun Feng wrote:
> > On Thu, Apr 18, 2024 at 03:56:11PM -0700, Boqun Feng wrote:
> >> On Thu, Apr 18, 2024 at 10:08:40PM +0000, Benno Lossin wrote:
> >>> On 18.04.24 20:52, Boqun Feng wrote:
> >>>> On Thu, Apr 18, 2024 at 08:59:20AM +0000, Alice Ryhl wrote:
> >>>>> + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
> >>>>> + ///
> >>>>> + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
> >>>>> + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
> >>>>> + /// this task, as this method uses a local mapping.
> >>>>> + ///
> >>>>> + /// If `off` and `len` refers to a region outside of this page, then this method returns
> >>>>> + /// `EINVAL` and does not call `f`.
> >>>>> + ///
> >>>>> + /// # Using the raw pointer
> >>>>> + ///
> >>>>> + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
> >>>>> + /// `len` bytes and for the duration in which the closure is called. The pointer might only be
> >>>>> + /// mapped on the current thread, and when that is the case, dereferencing it on other threads
> >>>>> + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
> >>>>> + /// data races, the memory may be uninitialized, and so on.
> >>>>> + ///
> >>>>> + /// If multiple threads map the same page at the same time, then they may reference with
> >>>>> + /// different addresses. However, even if the addresses are different, the underlying memory is
> >>>>> + /// still the same for these purposes (e.g., it's still a data race if they both write to the
> >>>>> + /// same underlying byte at the same time).
> >>>>> + fn with_pointer_into_page<T>(
> >>>>> + &self,
> >>>>> + off: usize,
> >>>>> + len: usize,
> >>>>> + f: impl FnOnce(*mut u8) -> Result<T>,
> >>>>
> >>>> I wonder whether the way to go here is making this function signature:
> >>>>
> >>>> fn with_slice_in_page<T> (
> >>>> &self,
> >>>> off: usize,
> >>>> len: usize,
> >>>> f: iml FnOnce(&UnsafeCell<[u8]>) -> Result<T>
> >>>> ) -> Result<T>
> >>>>
> >>>> , because in this way, it makes a bit more clear that what memory that
> >>>> `f` can access, in other words, the users are less likely to use the
> >>>> pointer in a wrong way.
> >>>>
> >>>> But that depends on whether `&UnsafeCell<[u8]>` is the correct
> >>>> abstraction and the ecosystem around it: for example, I feel like these
> >>>> two functions:
> >>>>
> >>>> fn len(slice: &UnsafeCell<[u8]>) -> usize
> >>>> fn as_ptr(slice: &UnsafeCell<[u8]>) -> *mut u8
> >>>>
> >>>> should be trivially safe, but I might be wrong. Again this is just for
> >>>> future discussion.
> >>>
> >>> I think the "better" type would be `&[UnsafeCell<u8>]`. Since there you
> >>> can always access the length.
> >>>
> >>
> >> Hmm.. here is the thing, having `&UnsafeCell<[u8]>` means having a `*mut
> >> [u8]>`, and it should always be safe to get a "length" of `*mut [u8]`,
> >> right? I haven't found any method doing that, but the length should be
> >> just a part of fat pointer, so I think getting that is a defined
> >> behavior. But maybe I'm missing something.
>
> There is `to_raw_parts` [1], but that is unstable. (Note that
> `<[T] as Pointee>::Metadata = usize`, see [2])
>
Oh, that's good to know, thank you! ;-)
> >>
> >
> > Hmm... but I guess one of the problems of this approach, is how to
> > construct a `&UnsafeCell<[u8]>` from a pointer and length...
>
> We could use `from_raw_parts` [3]. But when making the slice the outer
> type, we can use a stable function to convert a pointer and a length to
> a slice [4].
>
Yes, but there appears no way to get a pointer with larger provenance
from a `&[UnsafeCell<u8>]`, right?
> >
> > Regards,
> > Boqun
> >
> >>> Another question would be if page allows for uninitialized bits, in that
> >>> case, we would need `&[Opaque<u8>]`.
> >>>
> >>
> >> Yes, or `&Opaque<[u8>]`.
>
> I don't think that putting the slice on the inside is what we want. Also
Hmm.. why? So in `&UnsafeCell<[u8]>` vs `&[UnsafeCell<u8>]` case, I
think the former represent "a slice of u8 that can be modified in the
same time" very well, and this is what a pointer-and-length pair usually
represents in kernel, I think. But yes, the latter is OK to me as well,
just hard to play the provenance game I guess?
> note that `Opaque<T>` requires that `T: Sized` and that is not the case
> for `[u8]`.
Oh, you're right. In case of MaybeUninit, it requires `T: Sized`, so
`Opaque<[u8]>` doesn't quite work.
Moving forward, maybe the first step is to see whether `&[Opaque<u8>]`
and `&[UnsafeCell<u8>]` can have a good way to generate a pointer with
proper provenance? Time to ping t-opsem maybe?
Regards,
Boqun
>
> [1]: https://doc.rust-lang.org/nightly/core/primitive.pointer.html#method.to_raw_parts
> [2]: https://doc.rust-lang.org/nightly/core/ptr/trait.Pointee.html#pointer-metadata
> [3]: https://doc.rust-lang.org/nightly/core/ptr/fn.from_raw_parts.html
> [4]: https://doc.rust-lang.org/nightly/core/slice/fn.from_raw_parts.html
>
> --
> Cheers,
> Benno
>
On Fri, Apr 19, 2024 at 7:11 PM Boqun Feng <[email protected]> wrote:
>
> On Thu, Apr 18, 2024 at 08:59:17AM +0000, Alice Ryhl wrote:
> [...]
> > + /// Reads the entirety of the user slice, appending it to the end of the provided buffer.
> > + ///
> > + /// Fails with `EFAULT` if the read happens on a bad address.
> > + pub fn read_all(mut self, buf: &mut Vec<u8>, flags: Flags) -> Result {
> > + let len = self.length;
> > + buf.reserve(len, flags)?;
>
> (Reportedy by Miguel)
>
> When compile with `make rusttest`, kernel crate is compiled as userspace
> program, so we need to explicitly pick where the `reserve` comes from
> (Vec or VecExt), the current version will hit the following error:
>
> error[E0061]: this method takes 1 argument but 2 arguments were supplied
> --> rust/kernel/uaccess.rs:296:13
> |
> 296 | buf.reserve(len, flags)?;
> | ^^^^^^^ -------
> | | |
> | | unexpected argument of type `Flags`
> | help: remove the extra argument
> |
> note: method defined here
> --> /home/boqun/linux-rust/rust/test/sysroot/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:910:12
> |
> 910 | pub fn reserve(&mut self, additional: usize) {
> | ^^^^^^^
>
> error[E0277]: the `?` operator can only be applied to values that implement `Try`
> --> rust/kernel/uaccess.rs:296:9
> |
> 296 | buf.reserve(len, flags)?;
> | ^^^^^^^^^^^^^^^^^^^^^^^^ the `?` operator cannot be applied to type `()`
> |
> = help: the trait `Try` is not implemented for `()`
>
> error: aborting due to 2 previous errors
>
> Some errors have detailed explanations: E0061, E0277.
> For more information about an error, try `rustc --explain E0061`.
>
> and we need to the following fix
>
> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
> index 39481e374c40..80f7e7ca2f5e 100644
> --- a/rust/kernel/uaccess.rs
> +++ b/rust/kernel/uaccess.rs
> @@ -293,7 +293,7 @@ pub fn read<T: FromBytes>(&mut self) -> Result<T> {
> /// Fails with `EFAULT` if the read happens on a bad address.
> pub fn read_all(mut self, buf: &mut Vec<u8>, flags: Flags) -> Result {
> let len = self.length;
> - buf.reserve(len, flags)?;
> + VecExt::<u8>::reserve(buf, len, flags)?;
>
> // The call to `try_reserve` was successful, so the spare capacity is at least `len` bytes
> // long.
I'm sorry, what? This seems like a problem with `make rusttest`.
Alice
On 19.04.24 19:23, Boqun Feng wrote:
> On Fri, Apr 19, 2024 at 08:36:11AM +0000, Benno Lossin wrote:
>> On 19.04.24 01:04, Boqun Feng wrote:
>>> On Thu, Apr 18, 2024 at 03:56:11PM -0700, Boqun Feng wrote:
>>>> On Thu, Apr 18, 2024 at 10:08:40PM +0000, Benno Lossin wrote:
>>>>> On 18.04.24 20:52, Boqun Feng wrote:
>>>>>> On Thu, Apr 18, 2024 at 08:59:20AM +0000, Alice Ryhl wrote:
>>>>>>> + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
>>>>>>> + ///
>>>>>>> + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
>>>>>>> + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
>>>>>>> + /// this task, as this method uses a local mapping.
>>>>>>> + ///
>>>>>>> + /// If `off` and `len` refers to a region outside of this page, then this method returns
>>>>>>> + /// `EINVAL` and does not call `f`.
>>>>>>> + ///
>>>>>>> + /// # Using the raw pointer
>>>>>>> + ///
>>>>>>> + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
>>>>>>> + /// `len` bytes and for the duration in which the closure is called. The pointer might only be
>>>>>>> + /// mapped on the current thread, and when that is the case, dereferencing it on other threads
>>>>>>> + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
>>>>>>> + /// data races, the memory may be uninitialized, and so on.
>>>>>>> + ///
>>>>>>> + /// If multiple threads map the same page at the same time, then they may reference with
>>>>>>> + /// different addresses. However, even if the addresses are different, the underlying memory is
>>>>>>> + /// still the same for these purposes (e.g., it's still a data race if they both write to the
>>>>>>> + /// same underlying byte at the same time).
>>>>>>> + fn with_pointer_into_page<T>(
>>>>>>> + &self,
>>>>>>> + off: usize,
>>>>>>> + len: usize,
>>>>>>> + f: impl FnOnce(*mut u8) -> Result<T>,
>>>>>>
>>>>>> I wonder whether the way to go here is making this function signature:
>>>>>>
>>>>>> fn with_slice_in_page<T> (
>>>>>> &self,
>>>>>> off: usize,
>>>>>> len: usize,
>>>>>> f: iml FnOnce(&UnsafeCell<[u8]>) -> Result<T>
>>>>>> ) -> Result<T>
>>>>>>
>>>>>> , because in this way, it makes a bit more clear that what memory that
>>>>>> `f` can access, in other words, the users are less likely to use the
>>>>>> pointer in a wrong way.
>>>>>>
>>>>>> But that depends on whether `&UnsafeCell<[u8]>` is the correct
>>>>>> abstraction and the ecosystem around it: for example, I feel like these
>>>>>> two functions:
>>>>>>
>>>>>> fn len(slice: &UnsafeCell<[u8]>) -> usize
>>>>>> fn as_ptr(slice: &UnsafeCell<[u8]>) -> *mut u8
>>>>>>
>>>>>> should be trivially safe, but I might be wrong. Again this is just for
>>>>>> future discussion.
>>>>>
>>>>> I think the "better" type would be `&[UnsafeCell<u8>]`. Since there you
>>>>> can always access the length.
>>>>>
>>>>
>>>> Hmm.. here is the thing, having `&UnsafeCell<[u8]>` means having a `*mut
>>>> [u8]>`, and it should always be safe to get a "length" of `*mut [u8]`,
>>>> right? I haven't found any method doing that, but the length should be
>>>> just a part of fat pointer, so I think getting that is a defined
>>>> behavior. But maybe I'm missing something.
>>
>> There is `to_raw_parts` [1], but that is unstable. (Note that
>> `<[T] as Pointee>::Metadata = usize`, see [2])
>>
>
> Oh, that's good to know, thank you! ;-)
>
>>> Hmm... but I guess one of the problems of this approach, is how to
>>> construct a `&UnsafeCell<[u8]>` from a pointer and length...
>>
>> We could use `from_raw_parts` [3]. But when making the slice the outer
>> type, we can use a stable function to convert a pointer and a length to
>> a slice [4].
>>
>
> Yes, but there appears no way to get a pointer with larger provenance
> from a `&[UnsafeCell<u8>]`, right?
What do you mean by "larger provenance"?
>>>>> Another question would be if page allows for uninitialized bits, in that
>>>>> case, we would need `&[Opaque<u8>]`.
>>>>>
>>>>
>>>> Yes, or `&Opaque<[u8>]`.
>>
>> I don't think that putting the slice on the inside is what we want. Also
>
> Hmm.. why? So in `&UnsafeCell<[u8]>` vs `&[UnsafeCell<u8>]` case, I
> think the former represent "a slice of u8 that can be modified in the
> same time" very well, and this is what a pointer-and-length pair usually
> represents in kernel, I think. But yes, the latter is OK to me as well,
> just hard to play the provenance game I guess?
Ultimately it again comes down to missing field projections :)
The type `&UnsafeCell<[u8]>` is less *useful*, since you cannot even get
the length of the slice. Also indexing into this type is not easily
possible. This is because the only way to get/change the inner value of
an `UnsafeCell` is via `get`.
Compare this with the slice type. It allows getting the length, indexing
into it (ie a form of field projections, if we consider slices as having
a variable amount of fields).
All those issues would be solved by (good) field projections.
Field projections also give a reason for why using `&[UnsafeCell<u8>]`
is not really different from `&UnsafeCell<[u8]>`: At any point in time
we ought to be able to project `&UnsafeCell<[u8]> -> &[UnsafeCell<u8>]`.
So it's fine to just use that from the get-go.
>> note that `Opaque<T>` requires that `T: Sized` and that is not the case
>> for `[u8]`.
>
> Oh, you're right. In case of MaybeUninit, it requires `T: Sized`, so
> `Opaque<[u8]>` doesn't quite work.
>
> Moving forward, maybe the first step is to see whether `&[Opaque<u8>]`
> and `&[UnsafeCell<u8>]` can have a good way to generate a pointer with
> proper provenance? Time to ping t-opsem maybe?
Good idea, do you want to do that, or should I do it?
--
Cheers,
Benno
On Fri, Apr 19, 2024 at 07:24:31PM +0000, Benno Lossin wrote:
> On 19.04.24 19:23, Boqun Feng wrote:
> > On Fri, Apr 19, 2024 at 08:36:11AM +0000, Benno Lossin wrote:
> >> On 19.04.24 01:04, Boqun Feng wrote:
> >>> On Thu, Apr 18, 2024 at 03:56:11PM -0700, Boqun Feng wrote:
> >>>> On Thu, Apr 18, 2024 at 10:08:40PM +0000, Benno Lossin wrote:
> >>>>> On 18.04.24 20:52, Boqun Feng wrote:
> >>>>>> On Thu, Apr 18, 2024 at 08:59:20AM +0000, Alice Ryhl wrote:
> >>>>>>> + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
> >>>>>>> + ///
> >>>>>>> + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
> >>>>>>> + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
> >>>>>>> + /// this task, as this method uses a local mapping.
> >>>>>>> + ///
> >>>>>>> + /// If `off` and `len` refers to a region outside of this page, then this method returns
> >>>>>>> + /// `EINVAL` and does not call `f`.
> >>>>>>> + ///
> >>>>>>> + /// # Using the raw pointer
> >>>>>>> + ///
> >>>>>>> + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
> >>>>>>> + /// `len` bytes and for the duration in which the closure is called. The pointer might only be
> >>>>>>> + /// mapped on the current thread, and when that is the case, dereferencing it on other threads
> >>>>>>> + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
> >>>>>>> + /// data races, the memory may be uninitialized, and so on.
> >>>>>>> + ///
> >>>>>>> + /// If multiple threads map the same page at the same time, then they may reference with
> >>>>>>> + /// different addresses. However, even if the addresses are different, the underlying memory is
> >>>>>>> + /// still the same for these purposes (e.g., it's still a data race if they both write to the
> >>>>>>> + /// same underlying byte at the same time).
> >>>>>>> + fn with_pointer_into_page<T>(
> >>>>>>> + &self,
> >>>>>>> + off: usize,
> >>>>>>> + len: usize,
> >>>>>>> + f: impl FnOnce(*mut u8) -> Result<T>,
> >>>>>>
> >>>>>> I wonder whether the way to go here is making this function signature:
> >>>>>>
> >>>>>> fn with_slice_in_page<T> (
> >>>>>> &self,
> >>>>>> off: usize,
> >>>>>> len: usize,
> >>>>>> f: iml FnOnce(&UnsafeCell<[u8]>) -> Result<T>
> >>>>>> ) -> Result<T>
> >>>>>>
> >>>>>> , because in this way, it makes a bit more clear that what memory that
> >>>>>> `f` can access, in other words, the users are less likely to use the
> >>>>>> pointer in a wrong way.
> >>>>>>
> >>>>>> But that depends on whether `&UnsafeCell<[u8]>` is the correct
> >>>>>> abstraction and the ecosystem around it: for example, I feel like these
> >>>>>> two functions:
> >>>>>>
> >>>>>> fn len(slice: &UnsafeCell<[u8]>) -> usize
> >>>>>> fn as_ptr(slice: &UnsafeCell<[u8]>) -> *mut u8
> >>>>>>
> >>>>>> should be trivially safe, but I might be wrong. Again this is just for
> >>>>>> future discussion.
> >>>>>
> >>>>> I think the "better" type would be `&[UnsafeCell<u8>]`. Since there you
> >>>>> can always access the length.
> >>>>>
> >>>>
> >>>> Hmm.. here is the thing, having `&UnsafeCell<[u8]>` means having a `*mut
> >>>> [u8]>`, and it should always be safe to get a "length" of `*mut [u8]`,
> >>>> right? I haven't found any method doing that, but the length should be
> >>>> just a part of fat pointer, so I think getting that is a defined
> >>>> behavior. But maybe I'm missing something.
> >>
> >> There is `to_raw_parts` [1], but that is unstable. (Note that
> >> `<[T] as Pointee>::Metadata = usize`, see [2])
> >>
> >
> > Oh, that's good to know, thank you! ;-)
> >
> >>> Hmm... but I guess one of the problems of this approach, is how to
> >>> construct a `&UnsafeCell<[u8]>` from a pointer and length...
> >>
> >> We could use `from_raw_parts` [3]. But when making the slice the outer
> >> type, we can use a stable function to convert a pointer and a length to
> >> a slice [4].
> >>
> >
> > Yes, but there appears no way to get a pointer with larger provenance
> > from a `&[UnsafeCell<u8>]`, right?
>
> What do you mean by "larger provenance"?
>
Say you have a `&[UnsafeCell<u8>]` whose length is 64, what's the proper
way to get a `*mut u8` (or any other pointer) has the provenance for the
whole 64 bytes, so that you can pass it to a memcpy like function?
"larger" means the size of the provenance is larger than u8.
> >>>>> Another question would be if page allows for uninitialized bits, in that
> >>>>> case, we would need `&[Opaque<u8>]`.
> >>>>>
> >>>>
> >>>> Yes, or `&Opaque<[u8>]`.
> >>
> >> I don't think that putting the slice on the inside is what we want. Also
> >
> > Hmm.. why? So in `&UnsafeCell<[u8]>` vs `&[UnsafeCell<u8>]` case, I
> > think the former represent "a slice of u8 that can be modified in the
> > same time" very well, and this is what a pointer-and-length pair usually
> > represents in kernel, I think. But yes, the latter is OK to me as well,
> > just hard to play the provenance game I guess?
>
> Ultimately it again comes down to missing field projections :)
>
> The type `&UnsafeCell<[u8]>` is less *useful*, since you cannot even get
> the length of the slice. Also indexing into this type is not easily
> possible. This is because the only way to get/change the inner value of
> an `UnsafeCell` is via `get`.
>
> Compare this with the slice type. It allows getting the length, indexing
> into it (ie a form of field projections, if we consider slices as having
> a variable amount of fields).
>
> All those issues would be solved by (good) field projections.
>
>
> Field projections also give a reason for why using `&[UnsafeCell<u8>]`
> is not really different from `&UnsafeCell<[u8]>`: At any point in time
> we ought to be able to project `&UnsafeCell<[u8]> -> &[UnsafeCell<u8>]`.
>
Right, to me there is no significant difference between these two. Maybe
because I'm full field projected minded ;-)
> So it's fine to just use that from the get-go.
>
> >> note that `Opaque<T>` requires that `T: Sized` and that is not the case
> >> for `[u8]`.
> >
> > Oh, you're right. In case of MaybeUninit, it requires `T: Sized`, so
> > `Opaque<[u8]>` doesn't quite work.
> >
> > Moving forward, maybe the first step is to see whether `&[Opaque<u8>]`
> > and `&[UnsafeCell<u8>]` can have a good way to generate a pointer with
> > proper provenance? Time to ping t-opsem maybe?
>
> Good idea, do you want to do that, or should I do it?
>
A way to get a larger provenance (explained above) is currently my only
question, so if you think that's something reasonable to ask, i.e.
nothing you know of can help. I will post a message there.
Regards,
Boqun
> --
> Cheers,
> Benno
>
On Thu, 18 Apr 2024 15:56:11 -0700
Boqun Feng <[email protected]> wrote:
> Hmm.. here is the thing, having `&UnsafeCell<[u8]>` means having a `*mut
> [u8]>`, and it should always be safe to get a "length" of `*mut [u8]`,
> right? I haven't found any method doing that, but the length should be
> just a part of fat pointer, so I think getting that is a defined
> behavior. But maybe I'm missing something.
You can just use `unsafe_cell.get().len()`. `len` method exists on
raw slice pointers, gated by the `slice_ptr_len` feature, which will
be stable in 1.79.0.
Best,
Gary
On Thu, 18 Apr 2024 08:59:19 +0000
Alice Ryhl <[email protected]> wrote:
> Add safe methods for reading and writing Rust values to and from
> userspace pointers.
>
> The C methods for copying to/from userspace use a function called
> `check_object_size` to verify that the kernel pointer is not dangling.
> However, this check is skipped when the length is a compile-time
> constant, with the assumption that such cases trivially have a correct
> kernel pointer.
>
> In this patch, we apply the same optimization to the typed accessors.
> For both methods, the size of the operation is known at compile time to
> be size_of of the type being read or written. Since the C side doesn't
> provide a variant that skips only this check, we create custom helpers
> for this purpose.
>
> The majority of reads and writes to userspace pointers in the Rust
> Binder driver uses these accessor methods. Benchmarking has found that
> skipping the `check_object_size` check makes a big difference for the
> cases being skipped here. (And that the check doesn't make a difference
> for the cases that use the raw read/write methods.)
>
> This code is based on something that was originally written by Wedson on
> the old rust branch. It was modified by Alice to skip the
> `check_object_size` check, and to update various comments, including the
> notes about kernel pointers in `WritableToBytes`.
>
> Co-developed-by: Wedson Almeida Filho <[email protected]>
> Signed-off-by: Wedson Almeida Filho <[email protected]>
> Reviewed-by: Benno Lossin <[email protected]>
> Reviewed-by: Boqun Feng <[email protected]>
> Reviewed-by: Trevor Gross <[email protected]>
> Signed-off-by: Alice Ryhl <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
> ---
> rust/kernel/types.rs | 64 ++++++++++++++++++++++++++++++++++++++++
> rust/kernel/uaccess.rs | 79 ++++++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 141 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index 8fad61268465..9c57c6c75553 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
>
> +/// Types that can be viewed as an immutable slice of initialized bytes.
> +///
> +/// If a struct implements this trait, then it is okay to copy it byte-for-byte to userspace. This
> +/// means that it should not have any padding, as padding bytes are uninitialized. Reading
> +/// uninitialized memory is not just undefined behavior, it may even lead to leaking sensitive
> +/// information on the stack to userspace.
> +///
> +/// The struct should also not hold kernel pointers, as kernel pointer addresses are also considered
> +/// sensitive. However, leaking kernel pointers is not considered undefined behavior by Rust, so
> +/// this is a correctness requirement, but not a safety requirement.
> +///
> +/// # Safety
> +///
> +/// Values of this type may not contain any uninitialized bytes. This type must not have interior
> +/// mutability.
> +pub unsafe trait AsBytes {}
> +
> +// SAFETY: Instances of the following types have no uninitialized portions.
> +unsafe impl AsBytes for u8 {}
> +unsafe impl AsBytes for u16 {}
> +unsafe impl AsBytes for u32 {}
> +unsafe impl AsBytes for u64 {}
> +unsafe impl AsBytes for usize {}
> +unsafe impl AsBytes for i8 {}
> +unsafe impl AsBytes for i16 {}
> +unsafe impl AsBytes for i32 {}
> +unsafe impl AsBytes for i64 {}
> +unsafe impl AsBytes for isize {}
> +unsafe impl AsBytes for bool {}
> +unsafe impl AsBytes for char {}
> +unsafe impl AsBytes for str {}
> +// SAFETY: If individual values in an array have no uninitialized portions, then the array itself
> +// does not have any uninitialized portions either.
> +unsafe impl<T: AsBytes> AsBytes for [T] {}
nit: I would move `str` to here, since `str` is essentially `[u8]` with
UTF-8 guarantee.
> +unsafe impl<T: AsBytes, const N: usize> AsBytes for [T; N] {}
On Thu, Apr 25, 2024 at 6:14 PM Gary Guo <[email protected]> wrote:
>
> On Thu, 18 Apr 2024 08:59:19 +0000
> Alice Ryhl <[email protected]> wrote:
>
> > Add safe methods for reading and writing Rust values to and from
> > userspace pointers.
> >
> > The C methods for copying to/from userspace use a function called
> > `check_object_size` to verify that the kernel pointer is not dangling.
> > However, this check is skipped when the length is a compile-time
> > constant, with the assumption that such cases trivially have a correct
> > kernel pointer.
> >
> > In this patch, we apply the same optimization to the typed accessors.
> > For both methods, the size of the operation is known at compile time to
> > be size_of of the type being read or written. Since the C side doesn't
> > provide a variant that skips only this check, we create custom helpers
> > for this purpose.
> >
> > The majority of reads and writes to userspace pointers in the Rust
> > Binder driver uses these accessor methods. Benchmarking has found that
> > skipping the `check_object_size` check makes a big difference for the
> > cases being skipped here. (And that the check doesn't make a difference
> > for the cases that use the raw read/write methods.)
> >
> > This code is based on something that was originally written by Wedson on
> > the old rust branch. It was modified by Alice to skip the
> > `check_object_size` check, and to update various comments, including the
> > notes about kernel pointers in `WritableToBytes`.
> >
> > Co-developed-by: Wedson Almeida Filho <[email protected]>
> > Signed-off-by: Wedson Almeida Filho <[email protected]>
> > Reviewed-by: Benno Lossin <[email protected]>
> > Reviewed-by: Boqun Feng <[email protected]>
> > Reviewed-by: Trevor Gross <[email protected]>
> > Signed-off-by: Alice Ryhl <[email protected]>
>
> Reviewed-by: Gary Guo <[email protected]>
>
> > ---
> > rust/kernel/types.rs | 64 ++++++++++++++++++++++++++++++++++++++++
> > rust/kernel/uaccess.rs | 79 ++++++++++++++++++++++++++++++++++++++++++++++++--
> > 2 files changed, 141 insertions(+), 2 deletions(-)
> >
> > diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> > index 8fad61268465..9c57c6c75553 100644
> > --- a/rust/kernel/types.rs
> > +++ b/rust/kernel/types.rs
> >
> > +/// Types that can be viewed as an immutable slice of initialized bytes.
> > +///
> > +/// If a struct implements this trait, then it is okay to copy it byte-for-byte to userspace. This
> > +/// means that it should not have any padding, as padding bytes are uninitialized. Reading
> > +/// uninitialized memory is not just undefined behavior, it may even lead to leaking sensitive
> > +/// information on the stack to userspace.
> > +///
> > +/// The struct should also not hold kernel pointers, as kernel pointer addresses are also considered
> > +/// sensitive. However, leaking kernel pointers is not considered undefined behavior by Rust, so
> > +/// this is a correctness requirement, but not a safety requirement.
> > +///
> > +/// # Safety
> > +///
> > +/// Values of this type may not contain any uninitialized bytes. This type must not have interior
> > +/// mutability.
> > +pub unsafe trait AsBytes {}
> > +
> > +// SAFETY: Instances of the following types have no uninitialized portions.
> > +unsafe impl AsBytes for u8 {}
> > +unsafe impl AsBytes for u16 {}
> > +unsafe impl AsBytes for u32 {}
> > +unsafe impl AsBytes for u64 {}
> > +unsafe impl AsBytes for usize {}
> > +unsafe impl AsBytes for i8 {}
> > +unsafe impl AsBytes for i16 {}
> > +unsafe impl AsBytes for i32 {}
> > +unsafe impl AsBytes for i64 {}
> > +unsafe impl AsBytes for isize {}
> > +unsafe impl AsBytes for bool {}
> > +unsafe impl AsBytes for char {}
> > +unsafe impl AsBytes for str {}
> > +// SAFETY: If individual values in an array have no uninitialized portions, then the array itself
> > +// does not have any uninitialized portions either.
> > +unsafe impl<T: AsBytes> AsBytes for [T] {}
>
> nit: I would move `str` to here, since `str` is essentially `[u8]` with
> UTF-8 guarantee.
>
> > +unsafe impl<T: AsBytes, const N: usize> AsBytes for [T; N] {}
Yes ... but the safety comment here talks about arrays and their
individual values. I don't think it transfers cleanly to str, and that
the other safety comment fits str better.
Alice