The `module!` macro creates glue code that are called by C to initialize the Rust modules using the `Module::init` function. Part of this glue code are the local functions `__init` and `__exit` that are used to initialize/destroy the Rust module. These functions are safe and also visible to the Rust mod in which the `module!` macro is invoked. This means that they can be called by other safe Rust code. But since they contain `unsafe` blocks that rely on only being called at the right time, this is a soundness issue.

Wrap these generated functions inside of two private modules, this guarantees that the public functions cannot be called from the outside. Make the safe functions `unsafe` and add SAFETY comments.

Cc: stable@vger.kernel.org Closes: https://github.com/Rust-for-Linux/linux/issues/629 Fixes: 1fbde52bde73 ("rust: add `macros` crate") Signed-off-by: Benno Lossin benno.lossin@proton.me --- v1: https://lore.kernel.org/rust-for-linux/20240327160346.22442-1-benno.lossin@p... v1 -> v2: - wrapped `__init` and `__exit` calls in `unsafe` blocks and added SAFETY comments, - fixed safety requirement on `__exit` and `__init`, - rebased onto rust-next.

rust/macros/module.rs | 213 +++++++++++++++++++++++++----------------- 1 file changed, 127 insertions(+), 86 deletions(-)

diff --git a/rust/macros/module.rs b/rust/macros/module.rs index 27979e582e4b..293beca0a583 100644 --- a/rust/macros/module.rs +++ b/rust/macros/module.rs @@ -199,103 +199,144 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream { /// Used by the printing macros, e.g. [`info!`]. const __LOG_PREFIX: &[u8] = b"{name}\0";

- /// The "Rust loadable module" mark. - // - // This may be best done another way later on, e.g. as a new modinfo - // key or a new section. For the moment, keep it simple. - #[cfg(MODULE)] - #[doc(hidden)] - #[used] - static __IS_RUST_MODULE: () = (); - - static mut __MOD: Option<{type_}> = None; - - // SAFETY: `__this_module` is constructed by the kernel at load time and will not be - // freed until the module is unloaded. - #[cfg(MODULE)] - static THIS_MODULE: kernel::ThisModule = unsafe {{ - kernel::ThisModule::from_ptr(&kernel::bindings::__this_module as *const _ as *mut _) - }}; - #[cfg(not(MODULE))] - static THIS_MODULE: kernel::ThisModule = unsafe {{ - kernel::ThisModule::from_ptr(core::ptr::null_mut()) - }}; - - // Loadable modules need to export the `{{init,cleanup}}_module` identifiers. - /// # Safety - /// - /// This function must not be called after module initialization, because it may be - /// freed after that completes. - #[cfg(MODULE)] - #[doc(hidden)] - #[no_mangle] - #[link_section = ".init.text"] - pub unsafe extern "C" fn init_module() -> core::ffi::c_int {{ - __init() - }} + // Double nested modules, since then nobody can access the public items inside. + mod __module_init {{ + mod __module_init {{ + use super::super::{type_}; + + /// The "Rust loadable module" mark. + // + // This may be best done another way later on, e.g. as a new modinfo + // key or a new section. For the moment, keep it simple. + #[cfg(MODULE)] + #[doc(hidden)] + #[used] + static __IS_RUST_MODULE: () = (); + + static mut __MOD: Option<{type_}> = None; + + // SAFETY: `__this_module` is constructed by the kernel at load time and will not be + // freed until the module is unloaded. + #[cfg(MODULE)] + static THIS_MODULE: kernel::ThisModule = unsafe {{ + kernel::ThisModule::from_ptr(&kernel::bindings::__this_module as *const _ as *mut _) + }}; + #[cfg(not(MODULE))] + static THIS_MODULE: kernel::ThisModule = unsafe {{ + kernel::ThisModule::from_ptr(core::ptr::null_mut()) + }}; + + // Loadable modules need to export the `{{init,cleanup}}_module` identifiers. + /// # Safety + /// + /// This function must not be called after module initialization, because it may be + /// freed after that completes. + #[cfg(MODULE)] + #[doc(hidden)] + #[no_mangle] + #[link_section = ".init.text"] + pub unsafe extern "C" fn init_module() -> core::ffi::c_int {{ + // SAFETY: this function is inaccessible to the outside due to the double + // module wrapping it. It is called exactly once by the C side via its + // unique name. + unsafe {{ __init() }} + }}

- #[cfg(MODULE)] - #[doc(hidden)] - #[no_mangle] - pub extern "C" fn cleanup_module() {{ - __exit() - }} + #[cfg(MODULE)] + #[doc(hidden)] + #[no_mangle] + pub extern "C" fn cleanup_module() {{ + // SAFETY: + // - this function is inaccessible to the outside due to the double + // module wrapping it. It is called exactly once by the C side via its + // unique name, + // - furthermore it is only called after `init_module` has returned `0` + // (which delegates to `__init`). + unsafe {{ __exit() }} + }}

- // Built-in modules are initialized through an initcall pointer - // and the identifiers need to be unique. - #[cfg(not(MODULE))] - #[cfg(not(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS))] - #[doc(hidden)] - #[link_section = "{initcall_section}"] - #[used] - pub static __{name}_initcall: extern "C" fn() -> core::ffi::c_int = __{name}_init; - - #[cfg(not(MODULE))] - #[cfg(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)] - core::arch::global_asm!( - r#".section "{initcall_section}", "a" - __{name}_initcall: - .long __{name}_init - . - .previous - "# - ); + // Built-in modules are initialized through an initcall pointer + // and the identifiers need to be unique. + #[cfg(not(MODULE))] + #[cfg(not(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS))] + #[doc(hidden)] + #[link_section = "{initcall_section}"] + #[used] + pub static __{name}_initcall: extern "C" fn() -> core::ffi::c_int = __{name}_init; + + #[cfg(not(MODULE))] + #[cfg(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)] + core::arch::global_asm!( + r#".section "{initcall_section}", "a" + __{name}_initcall: + .long __{name}_init - . + .previous + "# + ); + + #[cfg(not(MODULE))] + #[doc(hidden)] + #[no_mangle] + pub extern "C" fn __{name}_init() -> core::ffi::c_int {{ + // SAFETY: this function is inaccessible to the outside due to the double + // module wrapping it. It is called exactly once by the C side via its + // placement above in the initcall section. + unsafe {{ __init() }} + }}

- #[cfg(not(MODULE))] - #[doc(hidden)] - #[no_mangle] - pub extern "C" fn __{name}_init() -> core::ffi::c_int {{ - __init() - }} + #[cfg(not(MODULE))] + #[doc(hidden)] + #[no_mangle] + pub extern "C" fn __{name}_exit() {{ + // SAFETY: + // - this function is inaccessible to the outside due to the double + // module wrapping it. It is called exactly once by the C side via its + // unique name, + // - furthermore it is only called after `__{name}_init` has returned `0` + // (which delegates to `__init`). + unsafe {{ __exit() }} + }}

- #[cfg(not(MODULE))] - #[doc(hidden)] - #[no_mangle] - pub extern "C" fn __{name}_exit() {{ - __exit() - }} + /// # Safety + /// + /// This function must only be called once. + unsafe fn __init() -> core::ffi::c_int {{ + match <{type_} as kernel::Module>::init(&THIS_MODULE) {{ + Ok(m) => {{ + // SAFETY: + // no data race, since `__MOD` can only be accessed by this module and + // there only `__init` and `__exit` access it. These functions are only + // called once and `__exit` cannot be called before or during `__init`. + unsafe {{ + __MOD = Some(m); + }} + return 0; + }} + Err(e) => {{ + return e.to_errno(); + }} + }} + }}

- fn __init() -> core::ffi::c_int {{ - match <{type_} as kernel::Module>::init(&THIS_MODULE) {{ - Ok(m) => {{ + /// # Safety + /// + /// This function must + /// - only be called once, + /// - be called after `__init` has been called and returned `0`. + unsafe fn __exit() {{ + // SAFETY: + // no data race, since `__MOD` can only be accessed by this module and there + // only `__init` and `__exit` access it. These functions are only called once + // and `__init` was already called. unsafe {{ - __MOD = Some(m); + // Invokes `drop()` on `__MOD`, which should be used for cleanup. + __MOD = None; }} - return 0; }} - Err(e) => {{ - return e.to_errno(); - }} - }} - }}

- fn __exit() {{ - unsafe {{ - // Invokes `drop()` on `__MOD`, which should be used for cleanup. - __MOD = None; + {modinfo} }} }} - - {modinfo} ", type_ = info.type_, name = info.name,

base-commit: 9ffe2a730313f27cebd0859ea856247ac59c576c