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The packed struct can be initialized as a whole by moving it into place. After all, a value of a packed struct is itself a valid initializer and is sound. If you have #[derive(Zeroable)] struct Foo { x: u8, y: u16, z: u8, } it is also valid to have `pin_init!(Foo { x: 1, ..Zeroable::zeroed() })` > require aligned pointers. This means that any code using packed structs > and pin-init is unsound. >=20 > Thus remove the `#[disable_initialized_field_access]` attribute from > `init!`, which is the only safe way to create an initializer of a packed > struct. >=20 > In the future, we can add support for packed structs by changing the > trait infrastructure to include `UnalignedInit` or hopefully another > mechanism. I guess the comment can be reworded a bit, to hint that this won't be added unless there's a compelling need, e.g. If support for in-place initializing packed structs is required in the future, we can ... Personally I think this won't be neeeded, as there are many ways around supporting unaligned fields, e.g. by creating and moving the entire packed structs. Another way is to use `Unaligned` type for fields that needs pin-init, similar to what zerocopy have. Best, Gary >=20 > Reported-by: Gary Guo > Link: https://rust-for-linux.zulipchat.com/#narrow/channel/561532-pin-ini= t/topic/initialized.20field.20accessor.20detection/with/576210658 [1] > Fixes: ceca298c53f9 ("rust: pin-init: internal: init: add escape hatch fo= r referencing initialized fields") > Signed-off-by: Benno Lossin > --- > This commit does not need backporting, as ceca298c53f9 is not yet in any > stable tree. >=20 > However, the unsoundness still affects several stable trees, because it > was unknowingly fixed in commit 42415d163e5d ("rust: pin-init: add > references to previously initialized fields"). Before then, packed > structs compiled without any issues with pin-init and thus all prior > kernel versions with pin-init that do not contain that commit are > affected. >=20 > We introduced pin-init in 90e53c5e70a6 ("rust: add pin-init API core"), > which was included in 6.4. The affected stable trees that are still > maintained are: 6.17, 6.16, 6.12, and 6.6. Note that 6.18 and 6.19 > already contain 42415d163e5d, so they are unaffected. >=20 > I will prepare a separate patch series to backport 42415d163e5d to each > of the affected trees, including the second patch of this series that > documents the fact that field accessors are load-bearing for soundness. >=20 > @asahi folks, let me know if I should prioritize a solution for packed > structs. Otherwise I'd like not support it at the moment, as that > requires some deeper changes to the internals of pin-init. I'm tracking > the status of packed structs in: >=20 > https://github.com/Rust-for-Linux/pin-init/issues/112 > --- > rust/pin-init/internal/src/init.rs | 39 ++++++------------------------ > 1 file changed, 8 insertions(+), 31 deletions(-)