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/crypto/sha1.c b/crypto/sha1.c
new file mode 100644
index 000000000..4fbf61cf0
--- /dev/null
+++ b/crypto/sha1.c
@@ -0,0 +1,240 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Crypto API support for SHA-1 and HMAC-SHA1
+ *
+ * Copyright (c) Alan Smithee.
+ * Copyright (c) Andrew McDonald <andrew@mcdonald.org.uk>
+ * Copyright (c) Jean-Francois Dive <jef@linuxbe.org>
+ * Copyright 2025 Google LLC
+ */
+#include <crypto/internal/hash.h>
+#include <crypto/sha1.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+/*
+ * Export and import functions.  crypto_shash wants a particular format that
+ * matches that used by some legacy drivers.  It currently is the same as the
+ * library SHA context, except the value in bytecount must be block-aligned and
+ * the remainder must be stored in an extra u8 appended to the struct.
+ */
+
+#define SHA1_SHASH_STATE_SIZE (sizeof(struct sha1_ctx) + 1)
+static_assert(sizeof(struct sha1_ctx) == sizeof(struct sha1_state));
+static_assert(offsetof(struct sha1_ctx, state) == offsetof(struct sha1_state, state));
+static_assert(offsetof(struct sha1_ctx, bytecount) == offsetof(struct sha1_state, count));
+static_assert(offsetof(struct sha1_ctx, buf) == offsetof(struct sha1_state, buffer));
+
+static int __crypto_sha1_export(const struct sha1_ctx *ctx0, void *out)
+{
+	struct sha1_ctx ctx = *ctx0;
+	unsigned int partial;
+	u8 *p = out;
+
+	partial = ctx.bytecount % SHA1_BLOCK_SIZE;
+	ctx.bytecount -= partial;
+	memcpy(p, &ctx, sizeof(ctx));
+	p += sizeof(ctx);
+	*p = partial;
+	return 0;
+}
+
+static int __crypto_sha1_import(struct sha1_ctx *ctx, const void *in)
+{
+	const u8 *p = in;
+
+	memcpy(ctx, p, sizeof(*ctx));
+	p += sizeof(*ctx);
+	ctx->bytecount += *p;
+	return 0;
+}
+
+static int __crypto_sha1_export_core(const struct sha1_ctx *ctx, void *out)
+{
+	memcpy(out, ctx, offsetof(struct sha1_ctx, buf));
+	return 0;
+}
+
+static int __crypto_sha1_import_core(struct sha1_ctx *ctx, const void *in)
+{
+	memcpy(ctx, in, offsetof(struct sha1_ctx, buf));
+	return 0;
+}
+
+const u8 sha1_zero_message_hash[SHA1_DIGEST_SIZE] = {
+	0xda, 0x39, 0xa3, 0xee, 0x5e, 0x6b, 0x4b, 0x0d,
+	0x32, 0x55, 0xbf, 0xef, 0x95, 0x60, 0x18, 0x90,
+	0xaf, 0xd8, 0x07, 0x09
+};
+EXPORT_SYMBOL_GPL(sha1_zero_message_hash);
+
+#define SHA1_CTX(desc) ((struct sha1_ctx *)shash_desc_ctx(desc))
+
+static int crypto_sha1_init(struct shash_desc *desc)
+{
+	sha1_init(SHA1_CTX(desc));
+	return 0;
+}
+
+static int crypto_sha1_update(struct shash_desc *desc,
+			      const u8 *data, unsigned int len)
+{
+	sha1_update(SHA1_CTX(desc), data, len);
+	return 0;
+}
+
+static int crypto_sha1_final(struct shash_desc *desc, u8 *out)
+{
+	sha1_final(SHA1_CTX(desc), out);
+	return 0;
+}
+
+static int crypto_sha1_digest(struct shash_desc *desc,
+			      const u8 *data, unsigned int len, u8 *out)
+{
+	sha1(data, len, out);
+	return 0;
+}
+
+static int crypto_sha1_export(struct shash_desc *desc, void *out)
+{
+	return __crypto_sha1_export(SHA1_CTX(desc), out);
+}
+
+static int crypto_sha1_import(struct shash_desc *desc, const void *in)
+{
+	return __crypto_sha1_import(SHA1_CTX(desc), in);
+}
+
+static int crypto_sha1_export_core(struct shash_desc *desc, void *out)
+{
+	return __crypto_sha1_export_core(SHA1_CTX(desc), out);
+}
+
+static int crypto_sha1_import_core(struct shash_desc *desc, const void *in)
+{
+	return __crypto_sha1_import_core(SHA1_CTX(desc), in);
+}
+
+#define HMAC_SHA1_KEY(tfm) ((struct hmac_sha1_key *)crypto_shash_ctx(tfm))
+#define HMAC_SHA1_CTX(desc) ((struct hmac_sha1_ctx *)shash_desc_ctx(desc))
+
+static int crypto_hmac_sha1_setkey(struct crypto_shash *tfm,
+				   const u8 *raw_key, unsigned int keylen)
+{
+	hmac_sha1_preparekey(HMAC_SHA1_KEY(tfm), raw_key, keylen);
+	return 0;
+}
+
+static int crypto_hmac_sha1_init(struct shash_desc *desc)
+{
+	hmac_sha1_init(HMAC_SHA1_CTX(desc), HMAC_SHA1_KEY(desc->tfm));
+	return 0;
+}
+
+static int crypto_hmac_sha1_update(struct shash_desc *desc,
+				   const u8 *data, unsigned int len)
+{
+	hmac_sha1_update(HMAC_SHA1_CTX(desc), data, len);
+	return 0;
+}
+
+static int crypto_hmac_sha1_final(struct shash_desc *desc, u8 *out)
+{
+	hmac_sha1_final(HMAC_SHA1_CTX(desc), out);
+	return 0;
+}
+
+static int crypto_hmac_sha1_digest(struct shash_desc *desc,
+				   const u8 *data, unsigned int len, u8 *out)
+{
+	hmac_sha1(HMAC_SHA1_KEY(desc->tfm), data, len, out);
+	return 0;
+}
+
+static int crypto_hmac_sha1_export(struct shash_desc *desc, void *out)
+{
+	return __crypto_sha1_export(&HMAC_SHA1_CTX(desc)->sha_ctx, out);
+}
+
+static int crypto_hmac_sha1_import(struct shash_desc *desc, const void *in)
+{
+	struct hmac_sha1_ctx *ctx = HMAC_SHA1_CTX(desc);
+
+	ctx->ostate = HMAC_SHA1_KEY(desc->tfm)->ostate;
+	return __crypto_sha1_import(&ctx->sha_ctx, in);
+}
+
+static int crypto_hmac_sha1_export_core(struct shash_desc *desc, void *out)
+{
+	return __crypto_sha1_export_core(&HMAC_SHA1_CTX(desc)->sha_ctx, out);
+}
+
+static int crypto_hmac_sha1_import_core(struct shash_desc *desc, const void *in)
+{
+	struct hmac_sha1_ctx *ctx = HMAC_SHA1_CTX(desc);
+
+	ctx->ostate = HMAC_SHA1_KEY(desc->tfm)->ostate;
+	return __crypto_sha1_import_core(&ctx->sha_ctx, in);
+}
+
+static struct shash_alg algs[] = {
+	{
+		.base.cra_name		= "sha1",
+		.base.cra_driver_name	= "sha1-lib",
+		.base.cra_priority	= 300,
+		.base.cra_blocksize	= SHA1_BLOCK_SIZE,
+		.base.cra_module	= THIS_MODULE,
+		.digestsize		= SHA1_DIGEST_SIZE,
+		.init			= crypto_sha1_init,
+		.update			= crypto_sha1_update,
+		.final			= crypto_sha1_final,
+		.digest			= crypto_sha1_digest,
+		.export			= crypto_sha1_export,
+		.import			= crypto_sha1_import,
+		.export_core		= crypto_sha1_export_core,
+		.import_core		= crypto_sha1_import_core,
+		.descsize		= sizeof(struct sha1_ctx),
+		.statesize		= SHA1_SHASH_STATE_SIZE,
+	},
+	{
+		.base.cra_name		= "hmac(sha1)",
+		.base.cra_driver_name	= "hmac-sha1-lib",
+		.base.cra_priority	= 300,
+		.base.cra_blocksize	= SHA1_BLOCK_SIZE,
+		.base.cra_ctxsize	= sizeof(struct hmac_sha1_key),
+		.base.cra_module	= THIS_MODULE,
+		.digestsize		= SHA1_DIGEST_SIZE,
+		.setkey			= crypto_hmac_sha1_setkey,
+		.init			= crypto_hmac_sha1_init,
+		.update			= crypto_hmac_sha1_update,
+		.final			= crypto_hmac_sha1_final,
+		.digest			= crypto_hmac_sha1_digest,
+		.export			= crypto_hmac_sha1_export,
+		.import			= crypto_hmac_sha1_import,
+		.export_core		= crypto_hmac_sha1_export_core,
+		.import_core		= crypto_hmac_sha1_import_core,
+		.descsize		= sizeof(struct hmac_sha1_ctx),
+		.statesize		= SHA1_SHASH_STATE_SIZE,
+	},
+};
+
+static int __init crypto_sha1_mod_init(void)
+{
+	return crypto_register_shashes(algs, ARRAY_SIZE(algs));
+}
+module_init(crypto_sha1_mod_init);
+
+static void __exit crypto_sha1_mod_exit(void)
+{
+	crypto_unregister_shashes(algs, ARRAY_SIZE(algs));
+}
+module_exit(crypto_sha1_mod_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Crypto API support for SHA-1 and HMAC-SHA1");
+
+MODULE_ALIAS_CRYPTO("sha1");
+MODULE_ALIAS_CRYPTO("sha1-lib");
+MODULE_ALIAS_CRYPTO("hmac(sha1)");
+MODULE_ALIAS_CRYPTO("hmac-sha1-lib");