kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 62 insertions, 0 deletions

diff --git a/include/crypto/mldsa.h b/include/crypto/mldsa.h
new file mode 100644
index 000000000..3ef267678
--- /dev/null
+++ b/include/crypto/mldsa.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Support for verifying ML-DSA signatures
+ *
+ * Copyright 2025 Google LLC
+ */
+#ifndef _CRYPTO_MLDSA_H
+#define _CRYPTO_MLDSA_H
+
+#include <linux/types.h>
+
+/* Identifier for an ML-DSA parameter set */
+enum mldsa_alg {
+	MLDSA44, /* ML-DSA-44 */
+	MLDSA65, /* ML-DSA-65 */
+	MLDSA87, /* ML-DSA-87 */
+};
+
+/* Lengths of ML-DSA public keys and signatures in bytes */
+#define MLDSA44_PUBLIC_KEY_SIZE 1312
+#define MLDSA65_PUBLIC_KEY_SIZE 1952
+#define MLDSA87_PUBLIC_KEY_SIZE 2592
+#define MLDSA44_SIGNATURE_SIZE 2420
+#define MLDSA65_SIGNATURE_SIZE 3309
+#define MLDSA87_SIGNATURE_SIZE 4627
+
+/**
+ * mldsa_verify() - Verify an ML-DSA signature
+ * @alg: The ML-DSA parameter set to use
+ * @sig: The signature
+ * @sig_len: Length of the signature in bytes.  Should match the
+ *	     MLDSA*_SIGNATURE_SIZE constant associated with @alg,
+ *	     otherwise -EBADMSG will be returned.
+ * @msg: The message
+ * @msg_len: Length of the message in bytes
+ * @pk: The public key
+ * @pk_len: Length of the public key in bytes.  Should match the
+ *	    MLDSA*_PUBLIC_KEY_SIZE constant associated with @alg,
+ *	    otherwise -EBADMSG will be returned.
+ *
+ * This verifies a signature using pure ML-DSA with the specified parameter set.
+ * The context string is assumed to be empty.  This corresponds to FIPS 204
+ * Algorithm 3 "ML-DSA.Verify" with the ctx parameter set to the empty string
+ * and the lengths of the signature and key given explicitly by the caller.
+ *
+ * Context: Might sleep
+ *
+ * Return:
+ * * 0 if the signature is valid
+ * * -EBADMSG if the signature and/or public key is malformed
+ * * -EKEYREJECTED if the signature is invalid but otherwise well-formed
+ * * -ENOMEM if out of memory so the validity of the signature is unknown
+ */
+int mldsa_verify(enum mldsa_alg alg, const u8 *sig, size_t sig_len,
+		 const u8 *msg, size_t msg_len, const u8 *pk, size_t pk_len);
+
+#if IS_ENABLED(CONFIG_CRYPTO_LIB_MLDSA_KUNIT_TEST)
+/* Internal function, exposed only for unit testing */
+s32 mldsa_use_hint(u8 h, s32 r, s32 gamma2);
+#endif
+
+#endif /* _CRYPTO_MLDSA_H */