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>

3 files changed, 414 insertions, 0 deletions

diff --git a/tools/testing/crypto/chacha20-s390/Makefile b/tools/testing/crypto/chacha20-s390/Makefile
new file mode 100644
index 000000000..db81cd2fb
--- /dev/null
+++ b/tools/testing/crypto/chacha20-s390/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2022 Red Hat, Inc.
+# Author: Vladis Dronov <vdronoff@gmail.com>
+
+obj-m += test_cipher.o
+test_cipher-y := test-cipher.o
+
+all:
+	make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules
+clean:
+	make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) clean
diff --git a/tools/testing/crypto/chacha20-s390/run-tests.sh b/tools/testing/crypto/chacha20-s390/run-tests.sh
new file mode 100644
index 000000000..43108794b
--- /dev/null
+++ b/tools/testing/crypto/chacha20-s390/run-tests.sh
@@ -0,0 +1,34 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2022 Red Hat, Inc.
+# Author: Vladis Dronov <vdronoff@gmail.com>
+#
+# This script runs (via instmod) test-cipher.ko module which invokes
+# generic and s390-native ChaCha20 encryprion algorithms with different
+# size of data. Check 'dmesg' for results.
+#
+# The insmod error is expected:
+# insmod: ERROR: could not insert module test_cipher.ko: Operation not permitted
+
+lsmod | grep chacha | cut -f1 -d' ' | xargs rmmod
+modprobe chacha_generic
+modprobe chacha_s390
+
+# run encryption for different data size, including whole block(s) +/- 1
+insmod test_cipher.ko size=63
+insmod test_cipher.ko size=64
+insmod test_cipher.ko size=65
+insmod test_cipher.ko size=127
+insmod test_cipher.ko size=128
+insmod test_cipher.ko size=129
+insmod test_cipher.ko size=511
+insmod test_cipher.ko size=512
+insmod test_cipher.ko size=513
+insmod test_cipher.ko size=4096
+insmod test_cipher.ko size=65611
+insmod test_cipher.ko size=6291456
+insmod test_cipher.ko size=62914560
+
+# print test logs
+dmesg | tail -170
diff --git a/tools/testing/crypto/chacha20-s390/test-cipher.c b/tools/testing/crypto/chacha20-s390/test-cipher.c
new file mode 100644
index 000000000..9f61454ed
--- /dev/null
+++ b/tools/testing/crypto/chacha20-s390/test-cipher.c
@@ -0,0 +1,368 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2022 Red Hat, Inc.
+ * Author: Vladis Dronov <vdronoff@gmail.com>
+ */
+
+#include <asm/elf.h>
+#include <asm/uaccess.h>
+#include <asm/smp.h>
+#include <crypto/skcipher.h>
+#include <crypto/akcipher.h>
+#include <crypto/acompress.h>
+#include <crypto/rng.h>
+#include <crypto/kpp.h>
+#include <crypto/internal/simd.h>
+#include <crypto/chacha.h>
+#include <crypto/aead.h>
+#include <crypto/hash.h>
+#include <linux/crypto.h>
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/fs.h>
+#include <linux/fips.h>
+#include <linux/kernel.h>
+#include <linux/kthread.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/scatterlist.h>
+#include <linux/time.h>
+#include <linux/vmalloc.h>
+#include <linux/zlib.h>
+#include <linux/once.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+static unsigned int data_size __read_mostly = 256;
+static unsigned int debug __read_mostly = 0;
+
+/* tie all skcipher structures together */
+struct skcipher_def {
+	struct scatterlist sginp, sgout;
+	struct crypto_skcipher *tfm;
+	struct skcipher_request *req;
+	struct crypto_wait wait;
+};
+
+/* Perform cipher operations with the chacha lib */
+static int test_lib_chacha(u8 *revert, u8 *cipher, u8 *plain)
+{
+	struct chacha_state chacha_state;
+	u8 iv[16], key[32];
+	u64 start, end;
+
+	memset(key, 'X', sizeof(key));
+	memset(iv, 'I', sizeof(iv));
+
+	if (debug) {
+		print_hex_dump(KERN_INFO, "key: ", DUMP_PREFIX_OFFSET,
+			       16, 1, key, 32, 1);
+
+		print_hex_dump(KERN_INFO, "iv:  ", DUMP_PREFIX_OFFSET,
+			       16, 1, iv, 16, 1);
+	}
+
+	/* Encrypt */
+	chacha_init(&chacha_state, (u32 *)key, iv);
+
+	start = ktime_get_ns();
+	chacha_crypt_arch(&chacha_state, cipher, plain, data_size, 20);
+	end = ktime_get_ns();
+
+
+	if (debug)
+		print_hex_dump(KERN_INFO, "encr:", DUMP_PREFIX_OFFSET,
+			       16, 1, cipher,
+			       (data_size > 64 ? 64 : data_size), 1);
+
+	pr_info("lib encryption took: %lld nsec", end - start);
+
+	/* Decrypt */
+	chacha_init(&chacha_state, (u32 *)key, iv);
+
+	start = ktime_get_ns();
+	chacha_crypt_arch(&chacha_state, revert, cipher, data_size, 20);
+	end = ktime_get_ns();
+
+	if (debug)
+		print_hex_dump(KERN_INFO, "decr:", DUMP_PREFIX_OFFSET,
+			       16, 1, revert,
+			       (data_size > 64 ? 64 : data_size), 1);
+
+	pr_info("lib decryption took: %lld nsec", end - start);
+
+	return 0;
+}
+
+/* Perform cipher operations with skcipher */
+static unsigned int test_skcipher_encdec(struct skcipher_def *sk,
+					 int enc)
+{
+	int rc;
+
+	if (enc) {
+		rc = crypto_wait_req(crypto_skcipher_encrypt(sk->req),
+				     &sk->wait);
+		if (rc)
+			pr_info("skcipher encrypt returned with result"
+				"%d\n", rc);
+	}
+	else
+	{
+		rc = crypto_wait_req(crypto_skcipher_decrypt(sk->req),
+				     &sk->wait);
+		if (rc)
+			pr_info("skcipher decrypt returned with result"
+				"%d\n", rc);
+	}
+
+	return rc;
+}
+
+/* Initialize and trigger cipher operations */
+static int test_skcipher(char *name, u8 *revert, u8 *cipher, u8 *plain)
+{
+	struct skcipher_def sk;
+	struct crypto_skcipher *skcipher = NULL;
+	struct skcipher_request *req = NULL;
+	u8 iv[16], key[32];
+	u64 start, end;
+	int ret = -EFAULT;
+
+	skcipher = crypto_alloc_skcipher(name, 0, 0);
+	if (IS_ERR(skcipher)) {
+		pr_info("could not allocate skcipher %s handle\n", name);
+		return PTR_ERR(skcipher);
+	}
+
+	req = skcipher_request_alloc(skcipher, GFP_KERNEL);
+	if (!req) {
+		pr_info("could not allocate skcipher request\n");
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
+					  crypto_req_done,
+					  &sk.wait);
+
+	memset(key, 'X', sizeof(key));
+	memset(iv, 'I', sizeof(iv));
+
+	if (crypto_skcipher_setkey(skcipher, key, 32)) {
+		pr_info("key could not be set\n");
+		ret = -EAGAIN;
+		goto out;
+	}
+
+	if (debug) {
+		print_hex_dump(KERN_INFO, "key: ", DUMP_PREFIX_OFFSET,
+			       16, 1, key, 32, 1);
+
+		print_hex_dump(KERN_INFO, "iv:  ", DUMP_PREFIX_OFFSET,
+			       16, 1, iv, 16, 1);
+	}
+
+	sk.tfm = skcipher;
+	sk.req = req;
+
+	/* Encrypt in one pass */
+	sg_init_one(&sk.sginp, plain, data_size);
+	sg_init_one(&sk.sgout, cipher, data_size);
+	skcipher_request_set_crypt(req, &sk.sginp, &sk.sgout,
+				   data_size, iv);
+	crypto_init_wait(&sk.wait);
+
+	/* Encrypt data */
+	start = ktime_get_ns();
+	ret = test_skcipher_encdec(&sk, 1);
+	end = ktime_get_ns();
+
+	if (ret)
+		goto out;
+
+	pr_info("%s tfm encryption successful, took %lld nsec\n", name, end - start);
+
+	if (debug)
+		print_hex_dump(KERN_INFO, "encr:", DUMP_PREFIX_OFFSET,
+			       16, 1, cipher,
+			       (data_size > 64 ? 64 : data_size), 1);
+
+	/* Prepare for decryption */
+	memset(iv, 'I', sizeof(iv));
+
+	sg_init_one(&sk.sginp, cipher, data_size);
+	sg_init_one(&sk.sgout, revert, data_size);
+	skcipher_request_set_crypt(req, &sk.sginp, &sk.sgout,
+				   data_size, iv);
+	crypto_init_wait(&sk.wait);
+
+	/* Decrypt data */
+	start = ktime_get_ns();
+	ret = test_skcipher_encdec(&sk, 0);
+	end = ktime_get_ns();
+
+	if (ret)
+		goto out;
+
+	pr_info("%s tfm decryption successful, took %lld nsec\n", name, end - start);
+
+	if (debug)
+		print_hex_dump(KERN_INFO, "decr:", DUMP_PREFIX_OFFSET,
+			       16, 1, revert,
+			       (data_size > 64 ? 64 : data_size), 1);
+
+	/* Dump some internal skcipher data */
+	if (debug)
+		pr_info("skcipher %s: cryptlen %d blksize %d stride %d "
+			"ivsize %d alignmask 0x%x\n",
+			name, sk.req->cryptlen,
+			crypto_skcipher_blocksize(sk.tfm),
+			crypto_skcipher_alg(sk.tfm)->walksize,
+			crypto_skcipher_ivsize(sk.tfm),
+			crypto_skcipher_alignmask(sk.tfm));
+
+out:
+	if (skcipher)
+		crypto_free_skcipher(skcipher);
+	if (req)
+		skcipher_request_free(req);
+	return ret;
+}
+
+static int __init chacha_s390_test_init(void)
+{
+	u8 *plain = NULL, *revert = NULL;
+	u8 *cipher_generic = NULL, *cipher_s390 = NULL;
+	int ret = -1;
+
+	pr_info("s390 ChaCha20 test module: size=%d debug=%d\n",
+		data_size, debug);
+
+	/* Allocate and fill buffers */
+	plain = vmalloc(data_size);
+	if (!plain) {
+		pr_info("could not allocate plain buffer\n");
+		ret = -2;
+		goto out;
+	}
+	memset(plain, 'a', data_size);
+	get_random_bytes(plain, (data_size > 256 ? 256 : data_size));
+
+	cipher_generic = vzalloc(data_size);
+	if (!cipher_generic) {
+		pr_info("could not allocate cipher_generic buffer\n");
+		ret = -2;
+		goto out;
+	}
+
+	cipher_s390 = vzalloc(data_size);
+	if (!cipher_s390) {
+		pr_info("could not allocate cipher_s390 buffer\n");
+		ret = -2;
+		goto out;
+	}
+
+	revert = vzalloc(data_size);
+	if (!revert) {
+		pr_info("could not allocate revert buffer\n");
+		ret = -2;
+		goto out;
+	}
+
+	if (debug)
+		print_hex_dump(KERN_INFO, "src: ", DUMP_PREFIX_OFFSET,
+			       16, 1, plain,
+			       (data_size > 64 ? 64 : data_size), 1);
+
+	/* Use chacha20 generic */
+	ret = test_skcipher("chacha20-generic", revert, cipher_generic, plain);
+	if (ret)
+		goto out;
+
+	if (memcmp(plain, revert, data_size)) {
+		pr_info("generic en/decryption check FAILED\n");
+		ret = -2;
+		goto out;
+	}
+	else
+		pr_info("generic en/decryption check OK\n");
+
+	memset(revert, 0, data_size);
+
+	/* Use chacha20 s390 */
+	ret = test_skcipher("chacha20-s390", revert, cipher_s390, plain);
+	if (ret)
+		goto out;
+
+	if (memcmp(plain, revert, data_size)) {
+		pr_info("s390 en/decryption check FAILED\n");
+		ret = -2;
+		goto out;
+	}
+	else
+		pr_info("s390 en/decryption check OK\n");
+
+	if (memcmp(cipher_generic, cipher_s390, data_size)) {
+		pr_info("s390 vs generic check FAILED\n");
+		ret = -2;
+		goto out;
+	}
+	else
+		pr_info("s390 vs generic check OK\n");
+
+	memset(cipher_s390, 0, data_size);
+	memset(revert, 0, data_size);
+
+	/* Use chacha20 lib */
+	test_lib_chacha(revert, cipher_s390, plain);
+
+	if (memcmp(plain, revert, data_size)) {
+		pr_info("lib en/decryption check FAILED\n");
+		ret = -2;
+		goto out;
+	}
+	else
+		pr_info("lib en/decryption check OK\n");
+
+	if (memcmp(cipher_generic, cipher_s390, data_size)) {
+		pr_info("lib vs generic check FAILED\n");
+		ret = -2;
+		goto out;
+	}
+	else
+		pr_info("lib vs generic check OK\n");
+
+	pr_info("--- chacha20 s390 test end ---\n");
+
+out:
+	if (plain)
+		vfree(plain);
+	if (cipher_generic)
+		vfree(cipher_generic);
+	if (cipher_s390)
+		vfree(cipher_s390);
+	if (revert)
+		vfree(revert);
+
+	return -1;
+}
+
+static void __exit chacha_s390_test_exit(void)
+{
+	pr_info("s390 ChaCha20 test module exit\n");
+}
+
+module_param_named(size, data_size, uint, 0660);
+module_param(debug, int, 0660);
+MODULE_PARM_DESC(size, "Size of a plaintext");
+MODULE_PARM_DESC(debug, "Debug level (0=off,1=on)");
+
+module_init(chacha_s390_test_init);
+module_exit(chacha_s390_test_exit);
+
+MODULE_DESCRIPTION("s390 ChaCha20 self-test");
+MODULE_AUTHOR("Vladis Dronov <vdronoff@gmail.com>");
+MODULE_LICENSE("GPL v2");