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, 493 insertions, 0 deletions

diff --git a/crypto/chacha20poly1305.c b/crypto/chacha20poly1305.c
new file mode 100644
index 000000000..27df9e1eb
--- /dev/null
+++ b/crypto/chacha20poly1305.c
@@ -0,0 +1,493 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * ChaCha20-Poly1305 AEAD, RFC7539
+ *
+ * Copyright (C) 2015 Martin Willi
+ */
+
+#include <crypto/internal/aead.h>
+#include <crypto/internal/hash.h>
+#include <crypto/internal/skcipher.h>
+#include <crypto/scatterwalk.h>
+#include <crypto/chacha.h>
+#include <crypto/poly1305.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+struct chachapoly_instance_ctx {
+	struct crypto_skcipher_spawn chacha;
+	unsigned int saltlen;
+};
+
+struct chachapoly_ctx {
+	struct crypto_skcipher *chacha;
+	/* key bytes we use for the ChaCha20 IV */
+	unsigned int saltlen;
+	u8 salt[] __counted_by(saltlen);
+};
+
+struct chacha_req {
+	u8 iv[CHACHA_IV_SIZE];
+	struct scatterlist src[1];
+	struct skcipher_request req; /* must be last member */
+};
+
+struct chachapoly_req_ctx {
+	struct scatterlist src[2];
+	struct scatterlist dst[2];
+	/* the key we generate for Poly1305 using Chacha20 */
+	u8 key[POLY1305_KEY_SIZE];
+	/* calculated Poly1305 tag */
+	u8 tag[POLY1305_DIGEST_SIZE];
+	/* length of data to en/decrypt, without ICV */
+	unsigned int cryptlen;
+	/* Actual AD, excluding IV */
+	unsigned int assoclen;
+	/* request flags, with MAY_SLEEP cleared if needed */
+	u32 flags;
+	union {
+		struct chacha_req chacha;
+	} u;
+};
+
+static inline void async_done_continue(struct aead_request *req, int err,
+				       int (*cont)(struct aead_request *))
+{
+	if (!err) {
+		struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+
+		rctx->flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
+		err = cont(req);
+	}
+
+	if (err != -EINPROGRESS && err != -EBUSY)
+		aead_request_complete(req, err);
+}
+
+static void chacha_iv(u8 *iv, struct aead_request *req, u32 icb)
+{
+	struct chachapoly_ctx *ctx = crypto_aead_ctx(crypto_aead_reqtfm(req));
+	__le32 leicb = cpu_to_le32(icb);
+
+	memcpy(iv, &leicb, sizeof(leicb));
+	memcpy(iv + sizeof(leicb), ctx->salt, ctx->saltlen);
+	memcpy(iv + sizeof(leicb) + ctx->saltlen, req->iv,
+	       CHACHA_IV_SIZE - sizeof(leicb) - ctx->saltlen);
+}
+
+static int poly_verify_tag(struct aead_request *req)
+{
+	struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+	u8 tag[sizeof(rctx->tag)];
+
+	scatterwalk_map_and_copy(tag, req->src,
+				 req->assoclen + rctx->cryptlen,
+				 sizeof(tag), 0);
+	if (crypto_memneq(tag, rctx->tag, sizeof(tag)))
+		return -EBADMSG;
+	return 0;
+}
+
+static void chacha_decrypt_done(void *data, int err)
+{
+	async_done_continue(data, err, poly_verify_tag);
+}
+
+static int chacha_decrypt(struct aead_request *req)
+{
+	struct chachapoly_ctx *ctx = crypto_aead_ctx(crypto_aead_reqtfm(req));
+	struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+	struct chacha_req *creq = &rctx->u.chacha;
+	struct scatterlist *src, *dst;
+	int err;
+
+	if (rctx->cryptlen == 0)
+		goto skip;
+
+	chacha_iv(creq->iv, req, 1);
+
+	src = scatterwalk_ffwd(rctx->src, req->src, req->assoclen);
+	dst = src;
+	if (req->src != req->dst)
+		dst = scatterwalk_ffwd(rctx->dst, req->dst, req->assoclen);
+
+	skcipher_request_set_callback(&creq->req, rctx->flags,
+				      chacha_decrypt_done, req);
+	skcipher_request_set_tfm(&creq->req, ctx->chacha);
+	skcipher_request_set_crypt(&creq->req, src, dst,
+				   rctx->cryptlen, creq->iv);
+	err = crypto_skcipher_decrypt(&creq->req);
+	if (err)
+		return err;
+
+skip:
+	return poly_verify_tag(req);
+}
+
+static int poly_hash(struct aead_request *req)
+{
+	struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+	const void *zp = page_address(ZERO_PAGE(0));
+	struct scatterlist *sg = req->src;
+	struct poly1305_desc_ctx desc;
+	struct scatter_walk walk;
+	struct {
+		union {
+			struct {
+				__le64 assoclen;
+				__le64 cryptlen;
+			};
+			u8 u8[16];
+		};
+	} tail;
+	unsigned int padlen;
+	unsigned int total;
+
+	if (sg != req->dst)
+		memcpy_sglist(req->dst, sg, req->assoclen);
+
+	if (rctx->cryptlen == req->cryptlen) /* encrypting */
+		sg = req->dst;
+
+	poly1305_init(&desc, rctx->key);
+	scatterwalk_start(&walk, sg);
+
+	total = rctx->assoclen;
+	while (total) {
+		unsigned int n = scatterwalk_next(&walk, total);
+
+		poly1305_update(&desc, walk.addr, n);
+		scatterwalk_done_src(&walk, n);
+		total -= n;
+	}
+
+	padlen = -rctx->assoclen % POLY1305_BLOCK_SIZE;
+	poly1305_update(&desc, zp, padlen);
+
+	scatterwalk_skip(&walk, req->assoclen - rctx->assoclen);
+
+	total = rctx->cryptlen;
+	while (total) {
+		unsigned int n = scatterwalk_next(&walk, total);
+
+		poly1305_update(&desc, walk.addr, n);
+		scatterwalk_done_src(&walk, n);
+		total -= n;
+	}
+
+	padlen = -rctx->cryptlen % POLY1305_BLOCK_SIZE;
+	poly1305_update(&desc, zp, padlen);
+
+	tail.assoclen = cpu_to_le64(rctx->assoclen);
+	tail.cryptlen = cpu_to_le64(rctx->cryptlen);
+	poly1305_update(&desc, tail.u8, sizeof(tail));
+	memzero_explicit(&tail, sizeof(tail));
+	poly1305_final(&desc, rctx->tag);
+
+	if (rctx->cryptlen != req->cryptlen)
+		return chacha_decrypt(req);
+
+	memcpy_to_scatterwalk(&walk, rctx->tag, sizeof(rctx->tag));
+	return 0;
+}
+
+static void poly_genkey_done(void *data, int err)
+{
+	async_done_continue(data, err, poly_hash);
+}
+
+static int poly_genkey(struct aead_request *req)
+{
+	struct crypto_aead *tfm = crypto_aead_reqtfm(req);
+	struct chachapoly_ctx *ctx = crypto_aead_ctx(tfm);
+	struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+	struct chacha_req *creq = &rctx->u.chacha;
+	int err;
+
+	rctx->assoclen = req->assoclen;
+
+	if (crypto_aead_ivsize(tfm) == 8) {
+		if (rctx->assoclen < 8)
+			return -EINVAL;
+		rctx->assoclen -= 8;
+	}
+
+	memset(rctx->key, 0, sizeof(rctx->key));
+	sg_init_one(creq->src, rctx->key, sizeof(rctx->key));
+
+	chacha_iv(creq->iv, req, 0);
+
+	skcipher_request_set_callback(&creq->req, rctx->flags,
+				      poly_genkey_done, req);
+	skcipher_request_set_tfm(&creq->req, ctx->chacha);
+	skcipher_request_set_crypt(&creq->req, creq->src, creq->src,
+				   POLY1305_KEY_SIZE, creq->iv);
+
+	err = crypto_skcipher_decrypt(&creq->req);
+	if (err)
+		return err;
+
+	return poly_hash(req);
+}
+
+static void chacha_encrypt_done(void *data, int err)
+{
+	async_done_continue(data, err, poly_genkey);
+}
+
+static int chacha_encrypt(struct aead_request *req)
+{
+	struct chachapoly_ctx *ctx = crypto_aead_ctx(crypto_aead_reqtfm(req));
+	struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+	struct chacha_req *creq = &rctx->u.chacha;
+	struct scatterlist *src, *dst;
+	int err;
+
+	if (req->cryptlen == 0)
+		goto skip;
+
+	chacha_iv(creq->iv, req, 1);
+
+	src = scatterwalk_ffwd(rctx->src, req->src, req->assoclen);
+	dst = src;
+	if (req->src != req->dst)
+		dst = scatterwalk_ffwd(rctx->dst, req->dst, req->assoclen);
+
+	skcipher_request_set_callback(&creq->req, rctx->flags,
+				      chacha_encrypt_done, req);
+	skcipher_request_set_tfm(&creq->req, ctx->chacha);
+	skcipher_request_set_crypt(&creq->req, src, dst,
+				   req->cryptlen, creq->iv);
+	err = crypto_skcipher_encrypt(&creq->req);
+	if (err)
+		return err;
+
+skip:
+	return poly_genkey(req);
+}
+
+static int chachapoly_encrypt(struct aead_request *req)
+{
+	struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+
+	rctx->cryptlen = req->cryptlen;
+	rctx->flags = aead_request_flags(req);
+
+	/* encrypt call chain:
+	 * - chacha_encrypt/done()
+	 * - poly_genkey/done()
+	 * - poly_hash()
+	 */
+	return chacha_encrypt(req);
+}
+
+static int chachapoly_decrypt(struct aead_request *req)
+{
+	struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
+
+	rctx->cryptlen = req->cryptlen - POLY1305_DIGEST_SIZE;
+	rctx->flags = aead_request_flags(req);
+
+	/* decrypt call chain:
+	 * - poly_genkey/done()
+	 * - poly_hash()
+	 * - chacha_decrypt/done()
+	 * - poly_verify_tag()
+	 */
+	return poly_genkey(req);
+}
+
+static int chachapoly_setkey(struct crypto_aead *aead, const u8 *key,
+			     unsigned int keylen)
+{
+	struct chachapoly_ctx *ctx = crypto_aead_ctx(aead);
+
+	if (keylen != ctx->saltlen + CHACHA_KEY_SIZE)
+		return -EINVAL;
+
+	keylen -= ctx->saltlen;
+	memcpy(ctx->salt, key + keylen, ctx->saltlen);
+
+	crypto_skcipher_clear_flags(ctx->chacha, CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_set_flags(ctx->chacha, crypto_aead_get_flags(aead) &
+					       CRYPTO_TFM_REQ_MASK);
+	return crypto_skcipher_setkey(ctx->chacha, key, keylen);
+}
+
+static int chachapoly_setauthsize(struct crypto_aead *tfm,
+				  unsigned int authsize)
+{
+	if (authsize != POLY1305_DIGEST_SIZE)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int chachapoly_init(struct crypto_aead *tfm)
+{
+	struct aead_instance *inst = aead_alg_instance(tfm);
+	struct chachapoly_instance_ctx *ictx = aead_instance_ctx(inst);
+	struct chachapoly_ctx *ctx = crypto_aead_ctx(tfm);
+	struct crypto_skcipher *chacha;
+	unsigned long align;
+
+	chacha = crypto_spawn_skcipher(&ictx->chacha);
+	if (IS_ERR(chacha))
+		return PTR_ERR(chacha);
+
+	ctx->chacha = chacha;
+	ctx->saltlen = ictx->saltlen;
+
+	align = crypto_aead_alignmask(tfm);
+	align &= ~(crypto_tfm_ctx_alignment() - 1);
+	crypto_aead_set_reqsize(
+		tfm,
+		align + offsetof(struct chachapoly_req_ctx, u) +
+		offsetof(struct chacha_req, req) +
+		sizeof(struct skcipher_request) +
+		crypto_skcipher_reqsize(chacha));
+
+	return 0;
+}
+
+static void chachapoly_exit(struct crypto_aead *tfm)
+{
+	struct chachapoly_ctx *ctx = crypto_aead_ctx(tfm);
+
+	crypto_free_skcipher(ctx->chacha);
+}
+
+static void chachapoly_free(struct aead_instance *inst)
+{
+	struct chachapoly_instance_ctx *ctx = aead_instance_ctx(inst);
+
+	crypto_drop_skcipher(&ctx->chacha);
+	kfree(inst);
+}
+
+static int chachapoly_create(struct crypto_template *tmpl, struct rtattr **tb,
+			     const char *name, unsigned int ivsize)
+{
+	u32 mask;
+	struct aead_instance *inst;
+	struct chachapoly_instance_ctx *ctx;
+	struct skcipher_alg_common *chacha;
+	const char *poly_name;
+	int err;
+
+	if (ivsize > CHACHAPOLY_IV_SIZE)
+		return -EINVAL;
+
+	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_AEAD, &mask);
+	if (err)
+		return err;
+
+	inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
+	if (!inst)
+		return -ENOMEM;
+	ctx = aead_instance_ctx(inst);
+	ctx->saltlen = CHACHAPOLY_IV_SIZE - ivsize;
+
+	err = crypto_grab_skcipher(&ctx->chacha, aead_crypto_instance(inst),
+				   crypto_attr_alg_name(tb[1]), 0, mask);
+	if (err)
+		goto err_free_inst;
+	chacha = crypto_spawn_skcipher_alg_common(&ctx->chacha);
+
+	poly_name = crypto_attr_alg_name(tb[2]);
+	if (IS_ERR(poly_name)) {
+		err = PTR_ERR(poly_name);
+		goto err_free_inst;
+	}
+
+	err = -EINVAL;
+	if (strcmp(poly_name, "poly1305") &&
+	    strcmp(poly_name, "poly1305-generic"))
+		goto err_free_inst;
+	/* Need 16-byte IV size, including Initial Block Counter value */
+	if (chacha->ivsize != CHACHA_IV_SIZE)
+		goto err_free_inst;
+	/* Not a stream cipher? */
+	if (chacha->base.cra_blocksize != 1)
+		goto err_free_inst;
+
+	err = -ENAMETOOLONG;
+	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
+		     "%s(%s,poly1305)", name,
+		     chacha->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
+		goto err_free_inst;
+	if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
+		     "%s(%s,poly1305-generic)", name,
+		     chacha->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
+		goto err_free_inst;
+
+	inst->alg.base.cra_priority = chacha->base.cra_priority;
+	inst->alg.base.cra_blocksize = 1;
+	inst->alg.base.cra_alignmask = chacha->base.cra_alignmask;
+	inst->alg.base.cra_ctxsize = sizeof(struct chachapoly_ctx) +
+				     ctx->saltlen;
+	inst->alg.ivsize = ivsize;
+	inst->alg.chunksize = chacha->chunksize;
+	inst->alg.maxauthsize = POLY1305_DIGEST_SIZE;
+	inst->alg.init = chachapoly_init;
+	inst->alg.exit = chachapoly_exit;
+	inst->alg.encrypt = chachapoly_encrypt;
+	inst->alg.decrypt = chachapoly_decrypt;
+	inst->alg.setkey = chachapoly_setkey;
+	inst->alg.setauthsize = chachapoly_setauthsize;
+
+	inst->free = chachapoly_free;
+
+	err = aead_register_instance(tmpl, inst);
+	if (err) {
+err_free_inst:
+		chachapoly_free(inst);
+	}
+	return err;
+}
+
+static int rfc7539_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	return chachapoly_create(tmpl, tb, "rfc7539", 12);
+}
+
+static int rfc7539esp_create(struct crypto_template *tmpl, struct rtattr **tb)
+{
+	return chachapoly_create(tmpl, tb, "rfc7539esp", 8);
+}
+
+static struct crypto_template rfc7539_tmpls[] = {
+	{
+		.name = "rfc7539",
+		.create = rfc7539_create,
+		.module = THIS_MODULE,
+	}, {
+		.name = "rfc7539esp",
+		.create = rfc7539esp_create,
+		.module = THIS_MODULE,
+	},
+};
+
+static int __init chacha20poly1305_module_init(void)
+{
+	return crypto_register_templates(rfc7539_tmpls,
+					 ARRAY_SIZE(rfc7539_tmpls));
+}
+
+static void __exit chacha20poly1305_module_exit(void)
+{
+	crypto_unregister_templates(rfc7539_tmpls,
+				    ARRAY_SIZE(rfc7539_tmpls));
+}
+
+module_init(chacha20poly1305_module_init);
+module_exit(chacha20poly1305_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Martin Willi <martin@strongswan.org>");
+MODULE_DESCRIPTION("ChaCha20-Poly1305 AEAD");
+MODULE_ALIAS_CRYPTO("rfc7539");
+MODULE_ALIAS_CRYPTO("rfc7539esp");