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a=openpgp-sha256; l=8588; i=aliceryhl@google.com; h=from:subject:message-id; bh=XaI6NH0XnJmRP4+EcHKB+RqgempmG+WN3YGnzXiE0G8=; b=owEBbQKS/ZANAwAKAQRYvu5YxjlGAcsmYgBnh7nAGt/I2v83P5iCzUqj5ZXeXUI8e+dMSkVQz nx0HwcJCmOJAjMEAAEKAB0WIQSDkqKUTWQHCvFIvbIEWL7uWMY5RgUCZ4e5wAAKCRAEWL7uWMY5 RjcSD/47K/3DO60B2Djq16CVAghmS7WUkxL/INITcyHRwb6oJ8YyJhj8TK4JqkPdRZkgehr6WpE UqWj8HfVf2ETduU02zEMH7DeWGL0InDF98h6k1ceM5BxZJZv3YkLzK/RHzERmuSBXNAjSh6dvLX 61fnzSxecO8s+2Wpew8AmqVgWbBGAjYEi+3VElElWycZMHTQqsu4s4Y3/9wnRBXF68JnTcaDPvI L/yuifcqD1EC8/mF6NiQkoW5S+gXPUOSUefteN9/S+ShXCUtGla0pyK2RzzAJqt1l6kP3p/nyzO OtLgYmlG7lSBWtX3opa/E1iQFE81tTvgbN1VGWVfp+ZW+HsGc8+Nij/6GNrobLS4GI98/75fpEj WRB78vEl0vEgcfRMi8GXtPKFWr0wwj7jhGbRpGutntjl46DzYxn4/lVriP/oGiGGPQHKXYc7LHU S3IuTdyr5eU5x9otUQ7z46m3ppB8ZooIYC/KFEUisOz9qkL4CSyyViR6UyM7AdpTrxG4gZOFCqg BNcWZr2LtyQm1HNI6UX61cMFt2zWQawXDoraJ1vfiImRSjc+IAZnDYnEKFyfoblOnhgLKv4SWGT +aE4UhZ5F9fPg5rnIYwlrOLeEhbbZ+f2FYtfsvVCemJTdoE5MikdWKLFvmu1AF7yL3LKhnDJ4S+ wcRVfT/ozzI9kkA== X-Mailer: b4 0.13.0 Message-ID: <20250115-vma-v12-6-375099ae017a@google.com> Subject: [PATCH v12 6/8] mm: rust: add VmAreaNew for f_ops->mmap() From: Alice Ryhl To: Miguel Ojeda , Matthew Wilcox , Lorenzo Stoakes , Vlastimil Babka , John Hubbard , "Liam R. Howlett" , Andrew Morton , Greg Kroah-Hartman , Arnd Bergmann , Jann Horn , Suren Baghdasaryan Cc: Alex Gaynor , Boqun Feng , Gary Guo , "=?utf-8?q?Bj=C3=B6rn_Roy_Baron?=" , Benno Lossin , Andreas Hindborg , Trevor Gross , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rust-for-linux@vger.kernel.org, Alice Ryhl Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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 (for mm bits) Reviewed-by: Jann Horn Signed-off-by: Alice Ryhl --- rust/kernel/mm/virt.rs | 186 +++++++++++++++++++++++++++++++++++++++++++++= +++- 1 file changed, 185 insertions(+), 1 deletion(-) diff --git a/rust/kernel/mm/virt.rs b/rust/kernel/mm/virt.rs index ab89a526d3e4..ef940973e231 100644 --- a/rust/kernel/mm/virt.rs +++ b/rust/kernel/mm/virt.rs @@ -16,7 +16,7 @@ =20 use crate::{ bindings, - error::{to_result, Result}, + error::{code::EINVAL, to_result, Result}, mm::MmWithUser, page::Page, types::Opaque, @@ -203,6 +203,190 @@ pub fn vm_insert_page(&self, address: usize, page: &P= age) -> Result { } } =20 +/// 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, an= d the hook is able to +/// configure the VMA in various ways to fit the driver that owns it. Usin= g `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 initiali= zation in an +/// `f_ops->mmap()` hook. +pub struct VmAreaNew { + vma: VmAreaRef, +} + +// Make all `VmAreaRef` methods available on `VmAreaNew`. +impl Deref for VmAreaNew { + type Target =3D 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 fo= r 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 =3D self.flags(); + flags |=3D set; + flags &=3D !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 u= sed to write in parallel. + // The caller promises that this does not set the flags to an inva= lid value. + unsafe { (*self.as_ptr()).__bindgen_anon_2.__vm_flags =3D flags }; + } + + /// Set the `VM_MIXEDMAP` flag on this vma. + /// + /// This enables the vma to contain both `struct page` and pure PFN pa= ges. 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 ca= nnot 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 othe= r 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 on= ly 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 opti= on 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 reada= ble. + #[inline] + pub fn readable(&self) -> bool { + (self.flags() & flags::READ) !=3D 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 be= en 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 writa= ble. + #[inline] + pub fn writable(&self) -> bool { + (self.flags() & flags::WRITE) !=3D 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 b= een 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 s= et. + unsafe { self.update_flags(0, flags::MAYWRITE) }; + Ok(()) + } + + /// Returns whether `VM_EXEC` is set. + /// + /// This flag indicates whether userspace is mapping this vma as execu= table. + #[inline] + pub fn executable(&self) -> bool { + (self.flags() & flags::EXEC) !=3D 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 be= en 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; --=20 2.48.0.rc2.279.g1de40edade-goog