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rust: pin-init: internal: init: remove `#[disable_initialized_field_access]` 

Gary noticed [1] that the initializer macros as well as the `[Pin]Init`
traits cannot support unaligned fields, since they use operations that
require aligned pointers. This means that any code using structs with
unaligned fields in pin-init is unsound.

By default, the `init!` macro generates references to initialized fields,
which makes the compiler check that those fields are aligned.  However,
we added the `#[disable_initialized_field_access]` attribute to avoid
this behavior in commit ceca298c53 ("rust: pin-init: internal: init:
add escape hatch for referencing initialized fields"). Thus remove the
`#[disable_initialized_field_access]` attribute from `init!`, which is
the only safe way to create an initializer handling unaligned fields.

If support for in-place initializing structs with unaligned fields is
required in the future, we could figure out a solution. This is tracked
in [2].

Reported-by: Gary Guo <gary@garyguo.net>
Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/561532-pin-init/topic/initialized.20field.20accessor.20detection/with/576210658 [1]
Link: https://github.com/Rust-for-Linux/pin-init/issues/112 [2]
Fixes: ceca298c53 ("rust: pin-init: internal: init: add escape hatch for referencing initialized fields")
Signed-off-by: Benno Lossin <lossin@kernel.org>
Acked-by: Janne Grunau <j@jannau.net>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20260302140424.4097655-1-lossin@kernel.org
[ Adjusted tags and reworded as discussed. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Benno Lossin 2026-03-02 15:04:14 +01:00 committed by Miguel Ojeda
parent dda135077e
commit a075082a15
1 changed files with 8 additions and 31 deletions
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39
rust/pin-init/internal/src/init.rs
View File

@ -62,7 +62,6 @@ impl InitializerKind {
enum InitializerAttribute {
DefaultError(DefaultErrorAttribute),
DisableInitializedFieldAccess,
}
struct DefaultErrorAttribute {
@ -86,6 +85,7 @@ pub(crate) fn expand(
let error = error.map_or_else(
|| {
if let Some(default_error) = attrs.iter().fold(None, |acc, attr| {
#[expect(irrefutable_let_patterns)]
if let InitializerAttribute::DefaultError(DefaultErrorAttribute { ty }) = attr {
Some(ty.clone())
} else {
@ -145,15 +145,7 @@ pub(crate) fn expand(
};
// `mixed_site` ensures that the data is not accessible to the user-controlled code.
let data = Ident::new("__data", Span::mixed_site());
let init_fields = init_fields(
&fields,
pinned,
!attrs
.iter()
.any(|attr| matches!(attr, InitializerAttribute::DisableInitializedFieldAccess)),
&data,
&slot,
);
let init_fields = init_fields(&fields, pinned, &data, &slot);
let field_check = make_field_check(&fields, init_kind, &path);
Ok(quote! {{
// We do not want to allow arbitrary returns, so we declare this type as the `Ok` return
@ -236,7 +228,6 @@ fn get_init_kind(rest: Option<(Token![..], Expr)>, dcx: &mut DiagCtxt) -> InitKi
fn init_fields(
fields: &Punctuated<InitializerField, Token![,]>,
pinned: bool,
generate_initialized_accessors: bool,
data: &Ident,
slot: &Ident,
) -> TokenStream {
@ -272,13 +263,6 @@ fn init_fields(
unsafe { &mut (*#slot).#ident }
}
};
let accessor = generate_initialized_accessors.then(|| {
quote! {
#(#cfgs)*
#[allow(unused_variables)]
let #ident = #accessor;
}
});
quote! {
#(#attrs)*
{
@ -286,7 +270,9 @@ fn init_fields(
// SAFETY: TODO
unsafe { #write(::core::ptr::addr_of_mut!((*#slot).#ident), #value_ident) };
}
#accessor
#(#cfgs)*
#[allow(unused_variables)]
let #ident = #accessor;
}
}
InitializerKind::Init { ident, value, .. } => {
@ -326,20 +312,15 @@ fn init_fields(
},
)
};
let accessor = generate_initialized_accessors.then(|| {
quote! {
#(#cfgs)*
#[allow(unused_variables)]
let #ident = #accessor;
}
});
quote! {
#(#attrs)*
{
let #init = #value;
#value_init
}
#accessor
#(#cfgs)*
#[allow(unused_variables)]
let #ident = #accessor;
}
}
InitializerKind::Code { block: value, .. } => quote! {
@ -466,10 +447,6 @@ impl Parse for Initializer {
if a.path().is_ident("default_error") {
a.parse_args::<DefaultErrorAttribute>()
.map(InitializerAttribute::DefaultError)
} else if a.path().is_ident("disable_initialized_field_access") {
a.meta
.require_path_only()
.map(|_| InitializerAttribute::DisableInitializedFieldAccess)
} else {
Err(syn::Error::new_spanned(a, "unknown initializer attribute"))
}