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, 219 insertions, 0 deletions

diff --git a/lib/crypto/arm64/aes.h b/lib/crypto/arm64/aes.h
new file mode 100644
index 000000000..9e9e45a6f
--- /dev/null
+++ b/lib/crypto/arm64/aes.h
@@ -0,0 +1,219 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * AES block cipher, optimized for ARM64
+ *
+ * Copyright (C) 2013 - 2017 Linaro Ltd <ard.biesheuvel@linaro.org>
+ * Copyright 2026 Google LLC
+ */
+
+#include <asm/neon.h>
+#include <asm/simd.h>
+#include <linux/unaligned.h>
+#include <linux/cpufeature.h>
+
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_neon);
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_aes);
+
+struct aes_block {
+	u8 b[AES_BLOCK_SIZE];
+};
+
+asmlinkage void __aes_arm64_encrypt(const u32 rk[], u8 out[AES_BLOCK_SIZE],
+				    const u8 in[AES_BLOCK_SIZE], int rounds);
+asmlinkage void __aes_arm64_decrypt(const u32 inv_rk[], u8 out[AES_BLOCK_SIZE],
+				    const u8 in[AES_BLOCK_SIZE], int rounds);
+asmlinkage void __aes_ce_encrypt(const u32 rk[], u8 out[AES_BLOCK_SIZE],
+				 const u8 in[AES_BLOCK_SIZE], int rounds);
+asmlinkage void __aes_ce_decrypt(const u32 inv_rk[], u8 out[AES_BLOCK_SIZE],
+				 const u8 in[AES_BLOCK_SIZE], int rounds);
+asmlinkage u32 __aes_ce_sub(u32 l);
+asmlinkage void __aes_ce_invert(struct aes_block *out,
+				const struct aes_block *in);
+asmlinkage void neon_aes_mac_update(u8 const in[], u32 const rk[], int rounds,
+				    size_t blocks, u8 dg[], int enc_before,
+				    int enc_after);
+
+/*
+ * Expand an AES key using the crypto extensions if supported and usable or
+ * generic code otherwise.  The expanded key format is compatible between the
+ * two cases.  The outputs are @rndkeys (required) and @inv_rndkeys (optional).
+ */
+static void aes_expandkey_arm64(u32 rndkeys[], u32 *inv_rndkeys,
+				const u8 *in_key, int key_len, int nrounds)
+{
+	/*
+	 * The AES key schedule round constants
+	 */
+	static u8 const rcon[] = {
+		0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36,
+	};
+
+	u32 kwords = key_len / sizeof(u32);
+	struct aes_block *key_enc, *key_dec;
+	int i, j;
+
+	if (!static_branch_likely(&have_aes) || unlikely(!may_use_simd())) {
+		aes_expandkey_generic(rndkeys, inv_rndkeys, in_key, key_len);
+		return;
+	}
+
+	for (i = 0; i < kwords; i++)
+		rndkeys[i] = get_unaligned_le32(&in_key[i * sizeof(u32)]);
+
+	scoped_ksimd() {
+		for (i = 0; i < sizeof(rcon); i++) {
+			u32 *rki = &rndkeys[i * kwords];
+			u32 *rko = rki + kwords;
+
+			rko[0] = ror32(__aes_ce_sub(rki[kwords - 1]), 8) ^
+				 rcon[i] ^ rki[0];
+			rko[1] = rko[0] ^ rki[1];
+			rko[2] = rko[1] ^ rki[2];
+			rko[3] = rko[2] ^ rki[3];
+
+			if (key_len == AES_KEYSIZE_192) {
+				if (i >= 7)
+					break;
+				rko[4] = rko[3] ^ rki[4];
+				rko[5] = rko[4] ^ rki[5];
+			} else if (key_len == AES_KEYSIZE_256) {
+				if (i >= 6)
+					break;
+				rko[4] = __aes_ce_sub(rko[3]) ^ rki[4];
+				rko[5] = rko[4] ^ rki[5];
+				rko[6] = rko[5] ^ rki[6];
+				rko[7] = rko[6] ^ rki[7];
+			}
+		}
+
+		/*
+		 * Generate the decryption keys for the Equivalent Inverse
+		 * Cipher.  This involves reversing the order of the round
+		 * keys, and applying the Inverse Mix Columns transformation on
+		 * all but the first and the last one.
+		 */
+		if (inv_rndkeys) {
+			key_enc = (struct aes_block *)rndkeys;
+			key_dec = (struct aes_block *)inv_rndkeys;
+			j = nrounds;
+
+			key_dec[0] = key_enc[j];
+			for (i = 1, j--; j > 0; i++, j--)
+				__aes_ce_invert(key_dec + i, key_enc + j);
+			key_dec[i] = key_enc[0];
+		}
+	}
+}
+
+static void aes_preparekey_arch(union aes_enckey_arch *k,
+				union aes_invkey_arch *inv_k,
+				const u8 *in_key, int key_len, int nrounds)
+{
+	aes_expandkey_arm64(k->rndkeys, inv_k ? inv_k->inv_rndkeys : NULL,
+			    in_key, key_len, nrounds);
+}
+
+/*
+ * This is here temporarily until the remaining AES mode implementations are
+ * migrated from arch/arm64/crypto/ to lib/crypto/arm64/.
+ */
+int ce_aes_expandkey(struct crypto_aes_ctx *ctx, const u8 *in_key,
+		     unsigned int key_len)
+{
+	if (aes_check_keylen(key_len) != 0)
+		return -EINVAL;
+	ctx->key_length = key_len;
+	aes_expandkey_arm64(ctx->key_enc, ctx->key_dec, in_key, key_len,
+			    6 + key_len / 4);
+	return 0;
+}
+EXPORT_SYMBOL(ce_aes_expandkey);
+
+EXPORT_SYMBOL_NS_GPL(neon_aes_ecb_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_ecb_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_cbc_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_cbc_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_cbc_cts_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_cbc_cts_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_ctr_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_xctr_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_xts_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_xts_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_essiv_cbc_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(neon_aes_essiv_cbc_decrypt, "CRYPTO_INTERNAL");
+
+EXPORT_SYMBOL_NS_GPL(ce_aes_ecb_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_ecb_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_cbc_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_cbc_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_cbc_cts_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_cbc_cts_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_ctr_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_xctr_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_xts_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_xts_decrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_essiv_cbc_encrypt, "CRYPTO_INTERNAL");
+EXPORT_SYMBOL_NS_GPL(ce_aes_essiv_cbc_decrypt, "CRYPTO_INTERNAL");
+#if IS_MODULE(CONFIG_CRYPTO_AES_ARM64_CE_CCM)
+EXPORT_SYMBOL_NS_GPL(ce_aes_mac_update, "CRYPTO_INTERNAL");
+#endif
+
+static void aes_encrypt_arch(const struct aes_enckey *key,
+			     u8 out[AES_BLOCK_SIZE],
+			     const u8 in[AES_BLOCK_SIZE])
+{
+	if (static_branch_likely(&have_aes) && likely(may_use_simd())) {
+		scoped_ksimd()
+			__aes_ce_encrypt(key->k.rndkeys, out, in, key->nrounds);
+	} else {
+		__aes_arm64_encrypt(key->k.rndkeys, out, in, key->nrounds);
+	}
+}
+
+static void aes_decrypt_arch(const struct aes_key *key,
+			     u8 out[AES_BLOCK_SIZE],
+			     const u8 in[AES_BLOCK_SIZE])
+{
+	if (static_branch_likely(&have_aes) && likely(may_use_simd())) {
+		scoped_ksimd()
+			__aes_ce_decrypt(key->inv_k.inv_rndkeys, out, in,
+					 key->nrounds);
+	} else {
+		__aes_arm64_decrypt(key->inv_k.inv_rndkeys, out, in,
+				    key->nrounds);
+	}
+}
+
+#if IS_ENABLED(CONFIG_CRYPTO_LIB_AES_CBC_MACS)
+#define aes_cbcmac_blocks_arch aes_cbcmac_blocks_arch
+static bool aes_cbcmac_blocks_arch(u8 h[AES_BLOCK_SIZE],
+				   const struct aes_enckey *key, const u8 *data,
+				   size_t nblocks, bool enc_before,
+				   bool enc_after)
+{
+	if (static_branch_likely(&have_neon) && likely(may_use_simd())) {
+		scoped_ksimd() {
+			if (static_branch_likely(&have_aes))
+				ce_aes_mac_update(data, key->k.rndkeys,
+						  key->nrounds, nblocks, h,
+						  enc_before, enc_after);
+			else
+				neon_aes_mac_update(data, key->k.rndkeys,
+						    key->nrounds, nblocks, h,
+						    enc_before, enc_after);
+		}
+		return true;
+	}
+	return false;
+}
+#endif /* CONFIG_CRYPTO_LIB_AES_CBC_MACS */
+
+#define aes_mod_init_arch aes_mod_init_arch
+static void aes_mod_init_arch(void)
+{
+	if (cpu_have_named_feature(ASIMD)) {
+		static_branch_enable(&have_neon);
+		if (cpu_have_named_feature(AES))
+			static_branch_enable(&have_aes);
+	}
+}