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FROMLIST: mm: rust: add VmAreaNew for f_ops->mmap()

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This type will be used when setting up a new vma in an f_ops->mmap()
hook. Using a separate type from VmAreaRef allows us to have a separate
set of operations that you are only able to use during the mmap() hook.
For example, the VM_MIXEDMAP flag must not be changed after the initial
setup that happens during the f_ops->mmap() hook.

To avoid setting invalid flag values, the methods for clearing
VM_MAYWRITE and similar involve a check of VM_WRITE, and return an error
if VM_WRITE is set. Trying to use `try_clear_maywrite` without checking
the return value results in a compilation error because the `Result`
type is marked #[must_use].

For now, there's only a method for VM_MIXEDMAP and not VM_PFNMAP. When
we add a VM_PFNMAP method, we will need some way to prevent you from
setting both VM_MIXEDMAP and VM_PFNMAP on the same vma.

Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> (for mm bits)
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>

Bug: 370906207
Link: https://lore.kernel.org/all/20250115-vma-v12-6-375099ae017a@google.com/
Change-Id: I3a0829a32ed7e05961eadf15c6266be9d54c2d92
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
This commit is contained in:
Alice Ryhl
2024-11-19 16:39:01 +01:00
parent a259f04a68
commit 7d1983ce89
1 changed files with 185 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
rust/kernel/mm/virt.rs
+185 -1
View File
@@ -16,7 +16,7 @@
use crate::{
bindings,
error::{to_result, Result},
error::{code::EINVAL, to_result, Result},
mm::MmWithUser,
page::Page,
types::Opaque,
@@ -203,6 +203,190 @@ impl VmAreaMixedMap {
}
}
/// A configuration object for setting up a VMA in an `f_ops->mmap()` hook.
///
/// The `f_ops->mmap()` hook is called when a new VMA is being created, and the hook is able to
/// configure the VMA in various ways to fit the driver that owns it. Using `VmAreaNew` indicates
/// that you are allowed to perform operations on the VMA that can only be performed before the VMA
/// is fully initialized.
///
/// # Invariants
///
/// For the duration of 'a, the referenced vma must be undergoing initialization in an
/// `f_ops->mmap()` hook.
pub struct VmAreaNew {
vma: VmAreaRef,
}
// Make all `VmAreaRef` methods available on `VmAreaNew`.
impl Deref for VmAreaNew {
type Target = VmAreaRef;
#[inline]
fn deref(&self) -> &VmAreaRef {
&self.vma
}
}
impl VmAreaNew {
/// Access a virtual memory area given a raw pointer.
///
/// # Safety
///
/// Callers must ensure that `vma` is undergoing initial vma setup for the duration of 'a.
#[inline]
pub unsafe fn from_raw<'a>(vma: *mut bindings::vm_area_struct) -> &'a Self {
// SAFETY: The caller ensures that the invariants are satisfied for the duration of 'a.
unsafe { &*vma.cast() }
}
/// Internal method for updating the vma flags.
///
/// # Safety
///
/// This must not be used to set the flags to an invalid value.
#[inline]
unsafe fn update_flags(&self, set: vm_flags_t, unset: vm_flags_t) {
let mut flags = self.flags();
flags |= set;
flags &= !unset;
// SAFETY: This is not a data race: the vma is undergoing initial setup, so it's not yet
// shared. Additionally, `VmAreaNew` is `!Sync`, so it cannot be used to write in parallel.
// The caller promises that this does not set the flags to an invalid value.
unsafe { (*self.as_ptr()).__bindgen_anon_2.__vm_flags = flags };
}
/// Set the `VM_MIXEDMAP` flag on this vma.
///
/// This enables the vma to contain both `struct page` and pure PFN pages. Returns a reference
/// that can be used to call `vm_insert_page` on the vma.
#[inline]
pub fn set_mixedmap(&self) -> &VmAreaMixedMap {
// SAFETY: We don't yet provide a way to set VM_PFNMAP, so this cannot put the flags in an
// invalid state.
unsafe { self.update_flags(flags::MIXEDMAP, 0) };
// SAFETY: We just set `VM_MIXEDMAP` on the vma.
unsafe { VmAreaMixedMap::from_raw(self.vma.as_ptr()) }
}
/// Set the `VM_IO` flag on this vma.
///
/// This is used for memory mapped IO and similar. The flag tells other parts of the kernel to
/// avoid looking at the pages. For memory mapped IO this is useful as accesses to the pages
/// could have side effects.
#[inline]
pub fn set_io(&self) {
// SAFETY: Setting the VM_IO flag is always okay.
unsafe { self.update_flags(flags::IO, 0) };
}
/// Set the `VM_DONTEXPAND` flag on this vma.
///
/// This prevents the vma from being expanded with `mremap()`.
#[inline]
pub fn set_dontexpand(&self) {
// SAFETY: Setting the VM_DONTEXPAND flag is always okay.
unsafe { self.update_flags(flags::DONTEXPAND, 0) };
}
/// Set the `VM_DONTCOPY` flag on this vma.
///
/// This prevents the vma from being copied on fork. This option is only permanent if `VM_IO`
/// is set.
#[inline]
pub fn set_dontcopy(&self) {
// SAFETY: Setting the VM_DONTCOPY flag is always okay.
unsafe { self.update_flags(flags::DONTCOPY, 0) };
}
/// Set the `VM_DONTDUMP` flag on this vma.
///
/// This prevents the vma from being included in core dumps. This option is only permanent if
/// `VM_IO` is set.
#[inline]
pub fn set_dontdump(&self) {
// SAFETY: Setting the VM_DONTDUMP flag is always okay.
unsafe { self.update_flags(flags::DONTDUMP, 0) };
}
/// Returns whether `VM_READ` is set.
///
/// This flag indicates whether userspace is mapping this vma as readable.
#[inline]
pub fn readable(&self) -> bool {
(self.flags() & flags::READ) != 0
}
/// Try to clear the `VM_MAYREAD` flag, failing if `VM_READ` is set.
///
/// This flag indicates whether userspace is allowed to make this vma readable with
/// `mprotect()`.
///
/// Note that this operation is irreversible. Once `VM_MAYREAD` has been cleared, it can never
/// be set again.
#[inline]
pub fn try_clear_mayread(&self) -> Result {
if self.readable() {
return Err(EINVAL);
}
// SAFETY: Clearing `VM_MAYREAD` is okay when `VM_READ` is not set.
unsafe { self.update_flags(0, flags::MAYREAD) };
Ok(())
}
/// Returns whether `VM_WRITE` is set.
///
/// This flag indicates whether userspace is mapping this vma as writable.
#[inline]
pub fn writable(&self) -> bool {
(self.flags() & flags::WRITE) != 0
}
/// Try to clear the `VM_MAYWRITE` flag, failing if `VM_WRITE` is set.
///
/// This flag indicates whether userspace is allowed to make this vma writable with
/// `mprotect()`.
///
/// Note that this operation is irreversible. Once `VM_MAYWRITE` has been cleared, it can never
/// be set again.
#[inline]
pub fn try_clear_maywrite(&self) -> Result {
if self.writable() {
return Err(EINVAL);
}
// SAFETY: Clearing `VM_MAYWRITE` is okay when `VM_WRITE` is not set.
unsafe { self.update_flags(0, flags::MAYWRITE) };
Ok(())
}
/// Returns whether `VM_EXEC` is set.
///
/// This flag indicates whether userspace is mapping this vma as executable.
#[inline]
pub fn executable(&self) -> bool {
(self.flags() & flags::EXEC) != 0
}
/// Try to clear the `VM_MAYEXEC` flag, failing if `VM_EXEC` is set.
///
/// This flag indicates whether userspace is allowed to make this vma executable with
/// `mprotect()`.
///
/// Note that this operation is irreversible. Once `VM_MAYEXEC` has been cleared, it can never
/// be set again.
#[inline]
pub fn try_clear_mayexec(&self) -> Result {
if self.executable() {
return Err(EINVAL);
}
// SAFETY: Clearing `VM_MAYEXEC` is okay when `VM_EXEC` is not set.
unsafe { self.update_flags(0, flags::MAYEXEC) };
Ok(())
}
}
/// The integer type used for vma flags.
#[doc(inline)]
pub use bindings::vm_flags_t;