Here records steps for building rust-out-of-tree-module on Ubuntu 24.04 HWE kernel 6.17.0-14-generic

Step

First Rust support in Ubuntu kernel is a separate package other than linux-header-... packages, so:

sudo apt install linux-lib-rust-`uname -r`

Then for HWE kernels, e.g. linux-hwe-6.17, /usr/src/linux-headers-6.17.0-14-generic/rust points to ../linux-hwe-6.17-lib-rust-6.17.0-14-generic/rust but folder installed from package linux-lib-rust-6.17.0-14-generic is linux-lib-rust-6.17.0-14-generic/rust, thus make a soft link:

cd /usr/src
sudo ln -s linux-lib-rust-6.17.0-14-generic  linux-hwe-6.17-lib-rust-6.17.0-14-generic

Then comes to compiler. If using a different compiler to that when compiling kernel, build script complains:

  RUSTC [M] rust_out_of_tree.o
error[E0514]: found crate `core` compiled by an incompatible version of rustc
  |
  = note: the following crate versions were found:
          crate `core` compiled by rustc 1.82.0 (f6e511eec 2024-10-15) (built from a source tarball): /usr/src/linux-lib-rust-6.17.0-14-generic/rust/libcore.rmeta
  = help: please recompile that crate using this compiler (rustc 1.85.0 (4d91de4e4 2025-02-17)) (consider running `cargo clean` first)

So install that version of rustc from apt:

sudo apt install rustc-1.82 rust-1.82-src

then build with this specific version:

make KDIR=/usr/src/linux-headers-$(uname -r) LLVM=1 RUSTC=rustc-1.82 -j16

Another error complaining unrecognized command line arguments appears:

  CC [M]  rust_out_of_tree.mod.o
clang: error: unknown argument: '-fconserve-stack'
clang: error: unsupported argument 'bounds-strict' to option '-fsanitize='
clang: error: unsupported option '-mrecord-mcount' for target 'x86_64-unknown-linux-gnu'

One of the workarounds/solutions is setting C compiler to gcc

make KDIR=/usr/src/linux-headers-$(uname -r) LLVM=1 RUSTC=rustc-1.82 CC=gcc

And load it into kernel and remove it

sudo insmod ./rust_out_of_tree.ko
sudo rmmod ./rust_out_of_tree.ko

Log from dmesg:

[500433.753777] rust_out_of_tree: loading out-of-tree module taints kernel.
[500433.753785] rust_out_of_tree: module verification failed: signature and/or required key missing - tainting kernel
[500433.754087] rust_out_of_tree: Rust out-of-tree sample (init)
[500443.206517] rust_out_of_tree: My numbers are [72, 108, 200]
[500443.206523] rust_out_of_tree: Rust out-of-tree sample (exit)