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, 264 insertions, 0 deletions

diff --git a/crypto/simd.c b/crypto/simd.c
new file mode 100644
index 000000000..4e29f7977
--- /dev/null
+++ b/crypto/simd.c
@@ -0,0 +1,264 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Shared crypto simd helpers
+ *
+ * Copyright (c) 2012 Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
+ * Copyright (c) 2016 Herbert Xu <herbert@gondor.apana.org.au>
+ * Copyright (c) 2019 Google LLC
+ *
+ * Based on aesni-intel_glue.c by:
+ *  Copyright (C) 2008, Intel Corp.
+ *    Author: Huang Ying <ying.huang@intel.com>
+ */
+
+/*
+ * Shared crypto SIMD helpers.  These functions dynamically create and register
+ * an AEAD algorithm that wraps another, internal algorithm.  The wrapper
+ * ensures that the internal algorithm is only executed in a context where SIMD
+ * instructions are usable, i.e. where may_use_simd() returns true.  If SIMD is
+ * already usable, the wrapper directly calls the internal algorithm.  Otherwise
+ * it defers execution to a workqueue via cryptd.
+ *
+ * This is an alternative to the internal algorithm implementing a fallback for
+ * the !may_use_simd() case itself.
+ *
+ * Note that the wrapper algorithm is asynchronous, i.e. it has the
+ * CRYPTO_ALG_ASYNC flag set.  Therefore it won't be found by users who
+ * explicitly allocate a synchronous algorithm.
+ */
+
+#include <crypto/cryptd.h>
+#include <crypto/internal/aead.h>
+#include <crypto/internal/simd.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/preempt.h>
+#include <asm/simd.h>
+
+struct simd_aead_alg {
+	const char *ialg_name;
+	struct aead_alg alg;
+};
+
+struct simd_aead_ctx {
+	struct cryptd_aead *cryptd_tfm;
+};
+
+static int simd_aead_setkey(struct crypto_aead *tfm, const u8 *key,
+				unsigned int key_len)
+{
+	struct simd_aead_ctx *ctx = crypto_aead_ctx(tfm);
+	struct crypto_aead *child = &ctx->cryptd_tfm->base;
+
+	crypto_aead_clear_flags(child, CRYPTO_TFM_REQ_MASK);
+	crypto_aead_set_flags(child, crypto_aead_get_flags(tfm) &
+				     CRYPTO_TFM_REQ_MASK);
+	return crypto_aead_setkey(child, key, key_len);
+}
+
+static int simd_aead_setauthsize(struct crypto_aead *tfm, unsigned int authsize)
+{
+	struct simd_aead_ctx *ctx = crypto_aead_ctx(tfm);
+	struct crypto_aead *child = &ctx->cryptd_tfm->base;
+
+	return crypto_aead_setauthsize(child, authsize);
+}
+
+static int simd_aead_encrypt(struct aead_request *req)
+{
+	struct crypto_aead *tfm = crypto_aead_reqtfm(req);
+	struct simd_aead_ctx *ctx = crypto_aead_ctx(tfm);
+	struct aead_request *subreq;
+	struct crypto_aead *child;
+
+	subreq = aead_request_ctx(req);
+	*subreq = *req;
+
+	if (!crypto_simd_usable() ||
+	    (in_atomic() && cryptd_aead_queued(ctx->cryptd_tfm)))
+		child = &ctx->cryptd_tfm->base;
+	else
+		child = cryptd_aead_child(ctx->cryptd_tfm);
+
+	aead_request_set_tfm(subreq, child);
+
+	return crypto_aead_encrypt(subreq);
+}
+
+static int simd_aead_decrypt(struct aead_request *req)
+{
+	struct crypto_aead *tfm = crypto_aead_reqtfm(req);
+	struct simd_aead_ctx *ctx = crypto_aead_ctx(tfm);
+	struct aead_request *subreq;
+	struct crypto_aead *child;
+
+	subreq = aead_request_ctx(req);
+	*subreq = *req;
+
+	if (!crypto_simd_usable() ||
+	    (in_atomic() && cryptd_aead_queued(ctx->cryptd_tfm)))
+		child = &ctx->cryptd_tfm->base;
+	else
+		child = cryptd_aead_child(ctx->cryptd_tfm);
+
+	aead_request_set_tfm(subreq, child);
+
+	return crypto_aead_decrypt(subreq);
+}
+
+static void simd_aead_exit(struct crypto_aead *tfm)
+{
+	struct simd_aead_ctx *ctx = crypto_aead_ctx(tfm);
+
+	cryptd_free_aead(ctx->cryptd_tfm);
+}
+
+static int simd_aead_init(struct crypto_aead *tfm)
+{
+	struct simd_aead_ctx *ctx = crypto_aead_ctx(tfm);
+	struct cryptd_aead *cryptd_tfm;
+	struct simd_aead_alg *salg;
+	struct aead_alg *alg;
+	unsigned reqsize;
+
+	alg = crypto_aead_alg(tfm);
+	salg = container_of(alg, struct simd_aead_alg, alg);
+
+	cryptd_tfm = cryptd_alloc_aead(salg->ialg_name, CRYPTO_ALG_INTERNAL,
+				       CRYPTO_ALG_INTERNAL);
+	if (IS_ERR(cryptd_tfm))
+		return PTR_ERR(cryptd_tfm);
+
+	ctx->cryptd_tfm = cryptd_tfm;
+
+	reqsize = max(crypto_aead_reqsize(cryptd_aead_child(cryptd_tfm)),
+		      crypto_aead_reqsize(&cryptd_tfm->base));
+	reqsize += sizeof(struct aead_request);
+
+	crypto_aead_set_reqsize(tfm, reqsize);
+
+	return 0;
+}
+
+static struct simd_aead_alg *simd_aead_create_compat(struct aead_alg *ialg,
+						     const char *algname,
+						     const char *drvname,
+						     const char *basename)
+{
+	struct simd_aead_alg *salg;
+	struct aead_alg *alg;
+	int err;
+
+	salg = kzalloc_obj(*salg);
+	if (!salg) {
+		salg = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	salg->ialg_name = basename;
+	alg = &salg->alg;
+
+	err = -ENAMETOOLONG;
+	if (snprintf(alg->base.cra_name, CRYPTO_MAX_ALG_NAME, "%s", algname) >=
+	    CRYPTO_MAX_ALG_NAME)
+		goto out_free_salg;
+
+	if (snprintf(alg->base.cra_driver_name, CRYPTO_MAX_ALG_NAME, "%s",
+		     drvname) >= CRYPTO_MAX_ALG_NAME)
+		goto out_free_salg;
+
+	alg->base.cra_flags = CRYPTO_ALG_ASYNC |
+		(ialg->base.cra_flags & CRYPTO_ALG_INHERITED_FLAGS);
+	alg->base.cra_priority = ialg->base.cra_priority;
+	alg->base.cra_blocksize = ialg->base.cra_blocksize;
+	alg->base.cra_alignmask = ialg->base.cra_alignmask;
+	alg->base.cra_module = ialg->base.cra_module;
+	alg->base.cra_ctxsize = sizeof(struct simd_aead_ctx);
+
+	alg->ivsize = ialg->ivsize;
+	alg->maxauthsize = ialg->maxauthsize;
+	alg->chunksize = ialg->chunksize;
+
+	alg->init = simd_aead_init;
+	alg->exit = simd_aead_exit;
+
+	alg->setkey = simd_aead_setkey;
+	alg->setauthsize = simd_aead_setauthsize;
+	alg->encrypt = simd_aead_encrypt;
+	alg->decrypt = simd_aead_decrypt;
+
+	err = crypto_register_aead(alg);
+	if (err)
+		goto out_free_salg;
+
+out:
+	return salg;
+
+out_free_salg:
+	kfree(salg);
+	salg = ERR_PTR(err);
+	goto out;
+}
+
+static void simd_aead_free(struct simd_aead_alg *salg)
+{
+	crypto_unregister_aead(&salg->alg);
+	kfree(salg);
+}
+
+int simd_register_aeads_compat(struct aead_alg *algs, int count,
+			       struct simd_aead_alg **simd_algs)
+{
+	int err;
+	int i;
+	const char *algname;
+	const char *drvname;
+	const char *basename;
+	struct simd_aead_alg *simd;
+
+	for (i = 0; i < count; i++) {
+		if (WARN_ON(strncmp(algs[i].base.cra_name, "__", 2) ||
+			    strncmp(algs[i].base.cra_driver_name, "__", 2)))
+			return -EINVAL;
+	}
+
+	err = crypto_register_aeads(algs, count);
+	if (err)
+		return err;
+
+	for (i = 0; i < count; i++) {
+		algname = algs[i].base.cra_name + 2;
+		drvname = algs[i].base.cra_driver_name + 2;
+		basename = algs[i].base.cra_driver_name;
+		simd = simd_aead_create_compat(algs + i, algname, drvname, basename);
+		err = PTR_ERR(simd);
+		if (IS_ERR(simd))
+			goto err_unregister;
+		simd_algs[i] = simd;
+	}
+	return 0;
+
+err_unregister:
+	simd_unregister_aeads(algs, count, simd_algs);
+	return err;
+}
+EXPORT_SYMBOL_GPL(simd_register_aeads_compat);
+
+void simd_unregister_aeads(struct aead_alg *algs, int count,
+			   struct simd_aead_alg **simd_algs)
+{
+	int i;
+
+	crypto_unregister_aeads(algs, count);
+
+	for (i = 0; i < count; i++) {
+		if (simd_algs[i]) {
+			simd_aead_free(simd_algs[i]);
+			simd_algs[i] = NULL;
+		}
+	}
+}
+EXPORT_SYMBOL_GPL(simd_unregister_aeads);
+
+MODULE_DESCRIPTION("Shared crypto SIMD helpers");
+MODULE_LICENSE("GPL");