From: Danilo Krummrich dakr@kernel.org
commit dd09538fb4093176a818fcecd45114430cc5840f upstream.
So far the kernel's `Box` and `Vec` types can't be used by userspace test cases, since all users of those types (e.g. `CString`) use kernel allocators for instantiation.
In order to allow userspace test cases to make use of such types as well, implement the `Cmalloc` allocator within the allocator_test module and type alias all kernel allocators to `Cmalloc`. The `Cmalloc` allocator uses libc's `realloc()` function as allocator backend.
Reviewed-by: Benno Lossin benno.lossin@proton.me Reviewed-by: Gary Guo gary@garyguo.net Signed-off-by: Danilo Krummrich dakr@kernel.org Link: https://lore.kernel.org/r/20241004154149.93856-26-dakr@kernel.org [ Removed the temporary `allow(dead_code)` as discussed in the list and fixed typo, added backticks. - Miguel ] Signed-off-by: Miguel Ojeda ojeda@kernel.org --- rust/kernel/alloc.rs | 1 - rust/kernel/alloc/allocator_test.rs | 89 ++++++++++++++++++++++++++--- 2 files changed, 81 insertions(+), 9 deletions(-)
diff --git a/rust/kernel/alloc.rs b/rust/kernel/alloc.rs index 049fca7a514d..c6024afa3739 100644 --- a/rust/kernel/alloc.rs +++ b/rust/kernel/alloc.rs @@ -215,7 +215,6 @@ unsafe fn free(ptr: NonNull<u8>, layout: Layout) { } }
-#[allow(dead_code)] /// Returns a properly aligned dangling pointer from the given `layout`. pub(crate) fn dangling_from_layout(layout: Layout) -> NonNull<u8> { let ptr = layout.align() as *mut u8; diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs index bd0cbcd93e52..54ca85964d4a 100644 --- a/rust/kernel/alloc/allocator_test.rs +++ b/rust/kernel/alloc/allocator_test.rs @@ -1,22 +1,95 @@ // SPDX-License-Identifier: GPL-2.0
+//! So far the kernel's `Box` and `Vec` types can't be used by userspace test cases, since all users +//! of those types (e.g. `CString`) use kernel allocators for instantiation. +//! +//! In order to allow userspace test cases to make use of such types as well, implement the +//! `Cmalloc` allocator within the allocator_test module and type alias all kernel allocators to +//! `Cmalloc`. The `Cmalloc` allocator uses libc's `realloc()` function as allocator backend. + #![allow(missing_docs)]
-use super::{AllocError, Allocator, Flags}; +use super::{flags::*, AllocError, Allocator, Flags}; use core::alloc::Layout; +use core::cmp; +use core::ptr; use core::ptr::NonNull;
-pub struct Kmalloc; +/// The userspace allocator based on libc. +pub struct Cmalloc; + +pub type Kmalloc = Cmalloc; pub type Vmalloc = Kmalloc; pub type KVmalloc = Kmalloc;
-unsafe impl Allocator for Kmalloc { +extern "C" { + #[link_name = "aligned_alloc"] + fn libc_aligned_alloc(align: usize, size: usize) -> *mut core::ffi::c_void; + + #[link_name = "free"] + fn libc_free(ptr: *mut core::ffi::c_void); +} + +// SAFETY: +// - memory remains valid until it is explicitly freed, +// - passing a pointer to a valid memory allocation created by this `Allocator` is always OK, +// - `realloc` provides the guarantees as provided in the `# Guarantees` section. +unsafe impl Allocator for Cmalloc { unsafe fn realloc( - _ptr: Option<NonNull<u8>>, - _layout: Layout, - _old_layout: Layout, - _flags: Flags, + ptr: Option<NonNull<u8>>, + layout: Layout, + old_layout: Layout, + flags: Flags, ) -> Result<NonNull<[u8]>, AllocError> { - panic!(); + let src = match ptr { + Some(src) => { + if old_layout.size() == 0 { + ptr::null_mut() + } else { + src.as_ptr() + } + } + None => ptr::null_mut(), + }; + + if layout.size() == 0 { + // SAFETY: `src` is either NULL or was previously allocated with this `Allocator` + unsafe { libc_free(src.cast()) }; + + return Ok(NonNull::slice_from_raw_parts( + crate::alloc::dangling_from_layout(layout), + 0, + )); + } + + // SAFETY: Returns either NULL or a pointer to a memory allocation that satisfies or + // exceeds the given size and alignment requirements. + let dst = unsafe { libc_aligned_alloc(layout.align(), layout.size()) } as *mut u8; + let dst = NonNull::new(dst).ok_or(AllocError)?; + + if flags.contains(__GFP_ZERO) { + // SAFETY: The preceding calls to `libc_aligned_alloc` and `NonNull::new` + // guarantee that `dst` points to memory of at least `layout.size()` bytes. + unsafe { dst.as_ptr().write_bytes(0, layout.size()) }; + } + + if !src.is_null() { + // SAFETY: + // - `src` has previously been allocated with this `Allocator`; `dst` has just been + // newly allocated, hence the memory regions do not overlap. + // - both` src` and `dst` are properly aligned and valid for reads and writes + unsafe { + ptr::copy_nonoverlapping( + src, + dst.as_ptr(), + cmp::min(layout.size(), old_layout.size()), + ) + }; + } + + // SAFETY: `src` is either NULL or was previously allocated with this `Allocator` + unsafe { libc_free(src.cast()) }; + + Ok(NonNull::slice_from_raw_parts(dst, layout.size())) } }