In Rust, producing an invalid value of any type is immediate undefined behavior (UB); this includes via zeroing memory. Therefore, since an uninhabited type has no valid values, producing any values at all for it is UB.
The Rust standard library type `core::convert::Infallible` is uninhabited, by virtue of having been declared as an enum with no cases, which always produces uninhabited types in Rust.
The current kernel code allows this UB to be triggered, for example by code like `Box::core::convert::Infallible::init(kernel::init::zeroed())`.
Thus, remove the implementation of `Zeroable` for `Infallible`, thereby avoiding the unsoundness (potential for future UB).
Cc: stable@vger.kernel.org Fixes: 38cde0bd7b67 ("rust: init: add `Zeroable` trait and `init::zeroed` function") Closes: https://github.com/Rust-for-Linux/pinned-init/pull/13 Signed-off-by: Laine Taffin Altman alexanderaltman@me.com Reviewed-by: Alice Ryhl aliceryhl@google.com Reviewed-by: Boqun Feng boqun.feng@gmail.com --- V3 -> V4: Address review nits; run checkpatch properly. V2 -> V3: Email formatting correction. V1 -> V2: Added more documentation to the comment, with links; also added more details to the commit message.
rust/kernel/init.rs | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs index 424257284d16..3859c7ff81b7 100644 --- a/rust/kernel/init.rs +++ b/rust/kernel/init.rs @@ -1292,8 +1292,15 @@ macro_rules! impl_zeroable { i8, i16, i32, i64, i128, isize, f32, f64,
- // SAFETY: These are ZSTs, there is nothing to zero. - {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, Infallible, (), + // Note: do not add uninhabited types (such as `!` or `core::convert::Infallible`) to this list; + // creating an instance of an uninhabited type is immediate undefined behavior. For more on + // uninhabited/empty types, consult The Rustonomicon: + // https://doc.rust-lang.org/stable/nomicon/exotic-sizes.html#empty-types The Rust Reference + // also has information on undefined behavior: + // https://doc.rust-lang.org/stable/reference/behavior-considered-undefined.htm... + // + // SAFETY: These are inhabited ZSTs; there is nothing to zero and a valid value exists. + {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, (),
// SAFETY: Type is allowed to take any value, including all zeros. {<T>} MaybeUninit<T>,
base-commit: c85af715cac0a951eea97393378e84bb49384734
On 03.04.24 23:06, Laine Taffin Altman wrote:
In Rust, producing an invalid value of any type is immediate undefined behavior (UB); this includes via zeroing memory. Therefore, since an uninhabited type has no valid values, producing any values at all for it is UB.
The Rust standard library type `core::convert::Infallible` is uninhabited, by virtue of having been declared as an enum with no cases, which always produces uninhabited types in Rust.
The current kernel code allows this UB to be triggered, for example by code like `Box::core::convert::Infallible::init(kernel::init::zeroed())`.
Thus, remove the implementation of `Zeroable` for `Infallible`, thereby avoiding the unsoundness (potential for future UB).
Cc: stable@vger.kernel.org Fixes: 38cde0bd7b67 ("rust: init: add `Zeroable` trait and `init::zeroed` function") Closes: https://github.com/Rust-for-Linux/pinned-init/pull/13 Signed-off-by: Laine Taffin Altman alexanderaltman@me.com Reviewed-by: Alice Ryhl aliceryhl@google.com Reviewed-by: Boqun Feng boqun.feng@gmail.com
Reviewed-by: Benno Lossin benno.lossin@proton.me
V3 -> V4: Address review nits; run checkpatch properly. V2 -> V3: Email formatting correction. V1 -> V2: Added more documentation to the comment, with links; also added more details to the commit message.
rust/kernel/init.rs | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs index 424257284d16..3859c7ff81b7 100644 --- a/rust/kernel/init.rs +++ b/rust/kernel/init.rs @@ -1292,8 +1292,15 @@ macro_rules! impl_zeroable { i8, i16, i32, i64, i128, isize, f32, f64,
- // SAFETY: These are ZSTs, there is nothing to zero.
- {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, Infallible, (),
// Note: do not add uninhabited types (such as `!` or `core::convert::Infallible`) to this list;
// creating an instance of an uninhabited type is immediate undefined behavior. For more on
// uninhabited/empty types, consult The Rustonomicon:
// https://doc.rust-lang.org/stable/nomicon/exotic-sizes.html#empty-types The Rust Reference
// also has information on undefined behavior:
// https://doc.rust-lang.org/stable/reference/behavior-considered-undefined.htm...
//
// SAFETY: These are inhabited ZSTs; there is nothing to zero and a valid value exists.
{<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, (),
// SAFETY: Type is allowed to take any value, including all zeros. {<T>} MaybeUninit<T>,
base-commit: c85af715cac0a951eea97393378e84bb49384734
I don't see this commit in the kernel tree, what did you specify as `--base` when running `git format`?
On Thu, Apr 4, 2024 at 11:01 AM Benno Lossin benno.lossin@proton.me wrote:
I don't see this commit in the kernel tree, what did you specify as `--base` when running `git format`?
Yeah, I don't have it either, but it seems to apply cleanly.
Cheers, Miguel
On Apr 4, 2024, at 4:03 AM, Miguel Ojeda miguel.ojeda.sandonis@gmail.com wrote:
On Thu, Apr 4, 2024 at 11:01 AM Benno Lossin benno.lossin@proton.me wrote:
I don't see this commit in the kernel tree, what did you specify as `--base` when running `git format`?
Yeah, I don't have it either, but it seems to apply cleanly.
Cheers, Miguel
I ran `git format-patch origin/master --base=origin/master`. I can’t imagine how that could have resulted in a nonexistent commit hash?
Thanks, Laine
On 04.04.24 19:28, Laine Taffin Altman wrote:
On Apr 4, 2024, at 4:03 AM, Miguel Ojeda miguel.ojeda.sandonis@gmail.com wrote:
On Thu, Apr 4, 2024 at 11:01 AM Benno Lossin benno.lossin@proton.me wrote:
I don't see this commit in the kernel tree, what did you specify as `--base` when running `git format`?
Yeah, I don't have it either, but it seems to apply cleanly.
Cheers, Miguel
I ran `git format-patch origin/master --base=origin/master`. I can’t imagine how that could have resulted in a nonexistent commit hash?
That heavily depends on what `origin/master` is. Is `origin` pointing to Torvald's git? In that case it would explain why we don't have that commit hash yet. Normally you should base your work on the tree listed in the `T:` entry of the subsystem in the MAINTAINERS file. In our case it is `rust-next`. But no worries, since it applies cleanly it should be fine for this patch. Just something to keep in mind if you submit any future patches.
On Apr 7, 2024, at 1:56 AM, Benno Lossin benno.lossin@proton.me wrote:
On 04.04.24 19:28, Laine Taffin Altman wrote:
On Apr 4, 2024, at 4:03 AM, Miguel Ojeda miguel.ojeda.sandonis@gmail.com wrote:
On Thu, Apr 4, 2024 at 11:01 AM Benno Lossin benno.lossin@proton.me wrote:
I don't see this commit in the kernel tree, what did you specify as `--base` when running `git format`?
Yeah, I don't have it either, but it seems to apply cleanly.
Cheers, Miguel
I ran `git format-patch origin/master --base=origin/master`. I can’t imagine how that could have resulted in a nonexistent commit hash?
That heavily depends on what `origin/master` is. Is `origin` pointing to Torvald's git? In that case it would explain why we don't have that commit hash yet. Normally you should base your work on the tree listed in the `T:` entry of the subsystem in the MAINTAINERS file. In our case it is `rust-next`. But no worries, since it applies cleanly it should be fine for this patch. Just something to keep in mind if you submit any future patches.
-- Cheers, Benno
Ah, that makes sense! Indeed it was pointing there. I’ll remember for next time!
Thanks, Laine
On Wed, Apr 3, 2024 at 11:07 PM Laine Taffin Altman alexanderaltman@me.com wrote:
In Rust, producing an invalid value of any type is immediate undefined behavior (UB); this includes via zeroing memory. Therefore, since an uninhabited type has no valid values, producing any values at all for it is UB.
The Rust standard library type `core::convert::Infallible` is uninhabited, by virtue of having been declared as an enum with no cases, which always produces uninhabited types in Rust.
The current kernel code allows this UB to be triggered, for example by code like `Box::core::convert::Infallible::init(kernel::init::zeroed())`.
Thus, remove the implementation of `Zeroable` for `Infallible`, thereby avoiding the unsoundness (potential for future UB).
Cc: stable@vger.kernel.org Fixes: 38cde0bd7b67 ("rust: init: add `Zeroable` trait and `init::zeroed` function") Closes: https://github.com/Rust-for-Linux/pinned-init/pull/13 Signed-off-by: Laine Taffin Altman alexanderaltman@me.com Reviewed-by: Alice Ryhl aliceryhl@google.com Reviewed-by: Boqun Feng boqun.feng@gmail.com
[ Reformatted the comment slightly. ]
Applied to `rust-fixes` -- thanks everyone! Please feel free to still send tags.
Cheers, Miguel
linux-stable-mirror@lists.linaro.org
-
Benno Lossin -
Laine Taffin Altman -
Miguel Ojeda