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rust: macros: fix soundness issue in module! macro
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: [email protected] Reported-by: Björn Roy Baron <[email protected]> Closes: Rust-for-Linux/linux#629 Fixes: 1fbde52 ("rust: add `macros` crate") Signed-off-by: Benno Lossin <[email protected]> Reviewed-by: Wedson Almeida Filho <[email protected]> Link: https://lore.kernel.org/r/[email protected] [ Moved `THIS_MODULE` out of the private-in-private modules since it should remain public, as Dirk Behme noticed [1]. Capitalized comments, avoided newline in non-list SAFETY comments and reworded to add Reported-by and newline. ] Link: https://rust-for-linux.zulipchat.com/#narrow/stream/291565-Help/topic/x/near/433512583 [1] Signed-off-by: Miguel Ojeda <[email protected]>
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‎rust/macros/module.rs

Lines changed: 115 additions & 75 deletions
Original file line numberDiff line numberDiff line change
@@ -199,17 +199,6 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
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/// Used by the printing macros, e.g. [`info!`].
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const __LOG_PREFIX: &[u8] = b\"{name}\\0\";
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/// The \"Rust loadable module\" mark.
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//
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// This may be best done another way later on, e.g. as a new modinfo
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// key or a new section. For the moment, keep it simple.
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#[cfg(MODULE)]
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#[doc(hidden)]
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#[used]
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static __IS_RUST_MODULE: () = ();
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static mut __MOD: Option<{type_}> = None;
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// SAFETY: `__this_module` is constructed by the kernel at load time and will not be
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// freed until the module is unloaded.
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#[cfg(MODULE)]
@@ -221,81 +210,132 @@ pub(crate) fn module(ts: TokenStream) -> TokenStream {
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kernel::ThisModule::from_ptr(core::ptr::null_mut())
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}};
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// Loadable modules need to export the `{{init,cleanup}}_module` identifiers.
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/// # Safety
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///
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/// This function must not be called after module initialization, because it may be
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/// freed after that completes.
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#[cfg(MODULE)]
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#[doc(hidden)]
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#[no_mangle]
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#[link_section = \".init.text\"]
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pub unsafe extern \"C\" fn init_module() -> core::ffi::c_int {{
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__init()
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}}
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#[cfg(MODULE)]
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#[doc(hidden)]
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#[no_mangle]
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pub extern \"C\" fn cleanup_module() {{
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__exit()
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}}
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// Double nested modules, since then nobody can access the public items inside.
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mod __module_init {{
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mod __module_init {{
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use super::super::{type_};
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/// The \"Rust loadable module\" mark.
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//
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// This may be best done another way later on, e.g. as a new modinfo
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// key or a new section. For the moment, keep it simple.
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#[cfg(MODULE)]
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#[doc(hidden)]
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#[used]
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static __IS_RUST_MODULE: () = ();
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static mut __MOD: Option<{type_}> = None;
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// Loadable modules need to export the `{{init,cleanup}}_module` identifiers.
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/// # Safety
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///
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/// This function must not be called after module initialization, because it may be
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/// freed after that completes.
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#[cfg(MODULE)]
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#[doc(hidden)]
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#[no_mangle]
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#[link_section = \".init.text\"]
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pub unsafe extern \"C\" fn init_module() -> core::ffi::c_int {{
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// SAFETY: This function is inaccessible to the outside due to the double
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// module wrapping it. It is called exactly once by the C side via its
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// unique name.
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unsafe {{ __init() }}
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}}
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// Built-in modules are initialized through an initcall pointer
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// and the identifiers need to be unique.
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#[cfg(not(MODULE))]
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#[cfg(not(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS))]
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#[doc(hidden)]
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#[link_section = \"{initcall_section}\"]
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#[used]
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pub static __{name}_initcall: extern \"C\" fn() -> core::ffi::c_int = __{name}_init;
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#[cfg(MODULE)]
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#[doc(hidden)]
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#[no_mangle]
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pub extern \"C\" fn cleanup_module() {{
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// SAFETY:
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// - This function is inaccessible to the outside due to the double
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// module wrapping it. It is called exactly once by the C side via its
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// unique name,
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// - furthermore it is only called after `init_module` has returned `0`
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// (which delegates to `__init`).
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unsafe {{ __exit() }}
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}}
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#[cfg(not(MODULE))]
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#[cfg(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)]
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core::arch::global_asm!(
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r#\".section \"{initcall_section}\", \"a\"
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__{name}_initcall:
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.long __{name}_init - .
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.previous
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\"#
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);
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// Built-in modules are initialized through an initcall pointer
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// and the identifiers need to be unique.
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#[cfg(not(MODULE))]
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#[cfg(not(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS))]
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#[doc(hidden)]
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#[link_section = \"{initcall_section}\"]
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#[used]
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pub static __{name}_initcall: extern \"C\" fn() -> core::ffi::c_int = __{name}_init;
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#[cfg(not(MODULE))]
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#[cfg(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS)]
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core::arch::global_asm!(
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r#\".section \"{initcall_section}\", \"a\"
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__{name}_initcall:
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.long __{name}_init - .
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.previous
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\"#
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);
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#[cfg(not(MODULE))]
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#[doc(hidden)]
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#[no_mangle]
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pub extern \"C\" fn __{name}_init() -> core::ffi::c_int {{
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// SAFETY: This function is inaccessible to the outside due to the double
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// module wrapping it. It is called exactly once by the C side via its
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// placement above in the initcall section.
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unsafe {{ __init() }}
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}}
262286
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#[cfg(not(MODULE))]
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#[doc(hidden)]
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#[no_mangle]
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pub extern \"C\" fn __{name}_init() -> core::ffi::c_int {{
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__init()
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}}
287+
#[cfg(not(MODULE))]
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#[doc(hidden)]
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#[no_mangle]
290+
pub extern \"C\" fn __{name}_exit() {{
291+
// SAFETY:
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// - This function is inaccessible to the outside due to the double
293+
// module wrapping it. It is called exactly once by the C side via its
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// unique name,
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// - furthermore it is only called after `__{name}_init` has returned `0`
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// (which delegates to `__init`).
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unsafe {{ __exit() }}
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}}
269299
270-
#[cfg(not(MODULE))]
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#[doc(hidden)]
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#[no_mangle]
273-
pub extern \"C\" fn __{name}_exit() {{
274-
__exit()
275-
}}
300+
/// # Safety
301+
///
302+
/// This function must only be called once.
303+
unsafe fn __init() -> core::ffi::c_int {{
304+
match <{type_} as kernel::Module>::init(&super::super::THIS_MODULE) {{
305+
Ok(m) => {{
306+
// SAFETY: No data race, since `__MOD` can only be accessed by this
307+
// module and there only `__init` and `__exit` access it. These
308+
// functions are only called once and `__exit` cannot be called
309+
// before or during `__init`.
310+
unsafe {{
311+
__MOD = Some(m);
312+
}}
313+
return 0;
314+
}}
315+
Err(e) => {{
316+
return e.to_errno();
317+
}}
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}}
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}}
276320
277-
fn __init() -> core::ffi::c_int {{
278-
match <{type_} as kernel::Module>::init(&THIS_MODULE) {{
279-
Ok(m) => {{
321+
/// # Safety
322+
///
323+
/// This function must
324+
/// - only be called once,
325+
/// - be called after `__init` has been called and returned `0`.
326+
unsafe fn __exit() {{
327+
// SAFETY: No data race, since `__MOD` can only be accessed by this module
328+
// and there only `__init` and `__exit` access it. These functions are only
329+
// called once and `__init` was already called.
280330
unsafe {{
281-
__MOD = Some(m);
331+
// Invokes `drop()` on `__MOD`, which should be used for cleanup.
332+
__MOD = None;
282333
}}
283-
return 0;
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}}
285-
Err(e) => {{
286-
return e.to_errno();
287334
}}
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}}
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}}
290335
291-
fn __exit() {{
292-
unsafe {{
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// Invokes `drop()` on `__MOD`, which should be used for cleanup.
294-
__MOD = None;
336+
{modinfo}
295337
}}
296338
}}
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{modinfo}
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",
300340
type_ = info.type_,
301341
name = info.name,

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