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, 240 insertions, 0 deletions

diff --git a/lib/crypto/powerpc/aes.h b/lib/crypto/powerpc/aes.h
new file mode 100644
index 000000000..5a36b637e
--- /dev/null
+++ b/lib/crypto/powerpc/aes.h
@@ -0,0 +1,240 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2015 Markus Stockhausen <stockhausen@collogia.de>
+ * Copyright (C) 2015 International Business Machines Inc.
+ * Copyright 2026 Google LLC
+ */
+#include <asm/simd.h>
+#include <asm/switch_to.h>
+#include <linux/cpufeature.h>
+#include <linux/jump_label.h>
+#include <linux/preempt.h>
+#include <linux/uaccess.h>
+
+#ifdef CONFIG_SPE
+
+EXPORT_SYMBOL_GPL(ppc_expand_key_128);
+EXPORT_SYMBOL_GPL(ppc_expand_key_192);
+EXPORT_SYMBOL_GPL(ppc_expand_key_256);
+EXPORT_SYMBOL_GPL(ppc_generate_decrypt_key);
+EXPORT_SYMBOL_GPL(ppc_encrypt_ecb);
+EXPORT_SYMBOL_GPL(ppc_decrypt_ecb);
+EXPORT_SYMBOL_GPL(ppc_encrypt_cbc);
+EXPORT_SYMBOL_GPL(ppc_decrypt_cbc);
+EXPORT_SYMBOL_GPL(ppc_crypt_ctr);
+EXPORT_SYMBOL_GPL(ppc_encrypt_xts);
+EXPORT_SYMBOL_GPL(ppc_decrypt_xts);
+
+void ppc_encrypt_aes(u8 *out, const u8 *in, const u32 *key_enc, u32 rounds);
+void ppc_decrypt_aes(u8 *out, const u8 *in, const u32 *key_dec, u32 rounds);
+
+static void spe_begin(void)
+{
+	/* disable preemption and save users SPE registers if required */
+	preempt_disable();
+	enable_kernel_spe();
+}
+
+static void spe_end(void)
+{
+	disable_kernel_spe();
+	/* reenable preemption */
+	preempt_enable();
+}
+
+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)
+{
+	if (key_len == AES_KEYSIZE_128)
+		ppc_expand_key_128(k->spe_enc_key, in_key);
+	else if (key_len == AES_KEYSIZE_192)
+		ppc_expand_key_192(k->spe_enc_key, in_key);
+	else
+		ppc_expand_key_256(k->spe_enc_key, in_key);
+
+	if (inv_k)
+		ppc_generate_decrypt_key(inv_k->spe_dec_key, k->spe_enc_key,
+					 key_len);
+}
+
+static void aes_encrypt_arch(const struct aes_enckey *key,
+			     u8 out[AES_BLOCK_SIZE],
+			     const u8 in[AES_BLOCK_SIZE])
+{
+	spe_begin();
+	ppc_encrypt_aes(out, in, key->k.spe_enc_key, key->nrounds / 2 - 1);
+	spe_end();
+}
+
+static void aes_decrypt_arch(const struct aes_key *key,
+			     u8 out[AES_BLOCK_SIZE],
+			     const u8 in[AES_BLOCK_SIZE])
+{
+	spe_begin();
+	ppc_decrypt_aes(out, in, key->inv_k.spe_dec_key, key->nrounds / 2 - 1);
+	spe_end();
+}
+
+#else /* CONFIG_SPE */
+
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_vec_crypto);
+
+EXPORT_SYMBOL_GPL(aes_p8_set_encrypt_key);
+EXPORT_SYMBOL_GPL(aes_p8_set_decrypt_key);
+EXPORT_SYMBOL_GPL(aes_p8_encrypt);
+EXPORT_SYMBOL_GPL(aes_p8_decrypt);
+EXPORT_SYMBOL_GPL(aes_p8_cbc_encrypt);
+EXPORT_SYMBOL_GPL(aes_p8_ctr32_encrypt_blocks);
+EXPORT_SYMBOL_GPL(aes_p8_xts_encrypt);
+EXPORT_SYMBOL_GPL(aes_p8_xts_decrypt);
+
+static inline bool is_vsx_format(const struct p8_aes_key *key)
+{
+	return key->nrounds != 0;
+}
+
+/*
+ * Convert a round key from VSX to generic format by reflecting all 16 bytes (if
+ * little endian) or reflecting the bytes in each 4-byte word (if big endian),
+ * and (if apply_inv_mix=true) applying InvMixColumn to each column.
+ *
+ * It would be nice if the VSX and generic key formats would be compatible.  But
+ * that's very difficult to do, with the assembly code having been borrowed from
+ * OpenSSL and also targeted to POWER8 rather than POWER9.
+ *
+ * Fortunately, this conversion should only be needed in extremely rare cases,
+ * possibly not at all in practice.  It's just included for full correctness.
+ */
+static void rndkey_from_vsx(u32 out[4], const u32 in[4], bool apply_inv_mix)
+{
+	const bool be = IS_ENABLED(CONFIG_CPU_BIG_ENDIAN);
+	u32 k0 = swab32(in[0]);
+	u32 k1 = swab32(in[1]);
+	u32 k2 = swab32(in[2]);
+	u32 k3 = swab32(in[3]);
+
+	if (apply_inv_mix) {
+		k0 = inv_mix_columns(k0);
+		k1 = inv_mix_columns(k1);
+		k2 = inv_mix_columns(k2);
+		k3 = inv_mix_columns(k3);
+	}
+	out[0] = be ? k0 : k3;
+	out[1] = be ? k1 : k2;
+	out[2] = be ? k2 : k1;
+	out[3] = be ? k3 : k0;
+}
+
+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)
+{
+	const int keybits = 8 * key_len;
+	int ret;
+
+	if (static_branch_likely(&have_vec_crypto) && likely(may_use_simd())) {
+		preempt_disable();
+		pagefault_disable();
+		enable_kernel_vsx();
+		ret = aes_p8_set_encrypt_key(in_key, keybits, &k->p8);
+		/*
+		 * aes_p8_set_encrypt_key() should never fail here, since the
+		 * key length was already validated.
+		 */
+		WARN_ON_ONCE(ret);
+		if (inv_k) {
+			ret = aes_p8_set_decrypt_key(in_key, keybits,
+						     &inv_k->p8);
+			/* ... and likewise for aes_p8_set_decrypt_key(). */
+			WARN_ON_ONCE(ret);
+		}
+		disable_kernel_vsx();
+		pagefault_enable();
+		preempt_enable();
+	} else {
+		aes_expandkey_generic(k->rndkeys,
+				      inv_k ? inv_k->inv_rndkeys : NULL,
+				      in_key, key_len);
+		/* Mark the key as using the generic format. */
+		k->p8.nrounds = 0;
+		if (inv_k)
+			inv_k->p8.nrounds = 0;
+	}
+}
+
+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_vec_crypto) &&
+	    likely(is_vsx_format(&key->k.p8) && may_use_simd())) {
+		preempt_disable();
+		pagefault_disable();
+		enable_kernel_vsx();
+		aes_p8_encrypt(in, out, &key->k.p8);
+		disable_kernel_vsx();
+		pagefault_enable();
+		preempt_enable();
+	} else if (unlikely(is_vsx_format(&key->k.p8))) {
+		/*
+		 * This handles (the hopefully extremely rare) case where a key
+		 * was prepared using the VSX optimized format, then encryption
+		 * is done in a context that cannot use VSX instructions.
+		 */
+		u32 rndkeys[AES_MAX_KEYLENGTH_U32];
+
+		for (int i = 0; i < 4 * (key->nrounds + 1); i += 4)
+			rndkey_from_vsx(&rndkeys[i],
+					&key->k.p8.rndkeys[i], false);
+		aes_encrypt_generic(rndkeys, key->nrounds, out, in);
+	} else {
+		aes_encrypt_generic(key->k.rndkeys, key->nrounds, out, in);
+	}
+}
+
+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_vec_crypto) &&
+	    likely(is_vsx_format(&key->inv_k.p8) && may_use_simd())) {
+		preempt_disable();
+		pagefault_disable();
+		enable_kernel_vsx();
+		aes_p8_decrypt(in, out, &key->inv_k.p8);
+		disable_kernel_vsx();
+		pagefault_enable();
+		preempt_enable();
+	} else if (unlikely(is_vsx_format(&key->inv_k.p8))) {
+		/*
+		 * This handles (the hopefully extremely rare) case where a key
+		 * was prepared using the VSX optimized format, then decryption
+		 * is done in a context that cannot use VSX instructions.
+		 */
+		u32 inv_rndkeys[AES_MAX_KEYLENGTH_U32];
+		int i;
+
+		rndkey_from_vsx(&inv_rndkeys[0],
+				&key->inv_k.p8.rndkeys[0], false);
+		for (i = 4; i < 4 * key->nrounds; i += 4) {
+			rndkey_from_vsx(&inv_rndkeys[i],
+					&key->inv_k.p8.rndkeys[i], true);
+		}
+		rndkey_from_vsx(&inv_rndkeys[i],
+				&key->inv_k.p8.rndkeys[i], false);
+		aes_decrypt_generic(inv_rndkeys, key->nrounds, out, in);
+	} else {
+		aes_decrypt_generic(key->inv_k.inv_rndkeys, key->nrounds,
+				    out, in);
+	}
+}
+
+#define aes_mod_init_arch aes_mod_init_arch
+static void aes_mod_init_arch(void)
+{
+	if (cpu_has_feature(CPU_FTR_ARCH_207S) &&
+	    (cur_cpu_spec->cpu_user_features2 & PPC_FEATURE2_VEC_CRYPTO))
+		static_branch_enable(&have_vec_crypto);
+}
+
+#endif /* !CONFIG_SPE */