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/deflate.c b/crypto/deflate.c
new file mode 100644
index 000000000..710ebba7c
--- /dev/null
+++ b/crypto/deflate.c
@@ -0,0 +1,264 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Cryptographic API.
+ *
+ * Deflate algorithm (RFC 1951), implemented here primarily for use
+ * by IPCOMP (RFC 3173 & RFC 2394).
+ *
+ * Copyright (c) 2003 James Morris <jmorris@intercode.com.au>
+ * Copyright (c) 2023 Google, LLC. <ardb@kernel.org>
+ * Copyright (c) 2025 Herbert Xu <herbert@gondor.apana.org.au>
+ */
+#include <crypto/internal/acompress.h>
+#include <crypto/scatterwalk.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/overflow.h>
+#include <linux/percpu.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/zlib.h>
+
+#define DEFLATE_DEF_LEVEL		Z_DEFAULT_COMPRESSION
+#define DEFLATE_DEF_WINBITS		11
+#define DEFLATE_DEF_MEMLEVEL		MAX_MEM_LEVEL
+
+struct deflate_stream {
+	struct z_stream_s stream;
+	u8 workspace[];
+};
+
+static DEFINE_MUTEX(deflate_stream_lock);
+
+static void *deflate_alloc_stream(void)
+{
+	size_t size = max(zlib_inflate_workspacesize(),
+			  zlib_deflate_workspacesize(-DEFLATE_DEF_WINBITS,
+						     DEFLATE_DEF_MEMLEVEL));
+	struct deflate_stream *ctx;
+
+	ctx = kvmalloc_flex(*ctx, workspace, size);
+	if (!ctx)
+		return ERR_PTR(-ENOMEM);
+
+	ctx->stream.workspace = ctx->workspace;
+
+	return ctx;
+}
+
+static void deflate_free_stream(void *ctx)
+{
+	kvfree(ctx);
+}
+
+static struct crypto_acomp_streams deflate_streams = {
+	.alloc_ctx = deflate_alloc_stream,
+	.free_ctx = deflate_free_stream,
+};
+
+static int deflate_compress_one(struct acomp_req *req,
+				struct deflate_stream *ds)
+{
+	struct z_stream_s *stream = &ds->stream;
+	struct acomp_walk walk;
+	int ret;
+
+	ret = acomp_walk_virt(&walk, req, true);
+	if (ret)
+		return ret;
+
+	do {
+		unsigned int dcur;
+
+		dcur = acomp_walk_next_dst(&walk);
+		if (!dcur)
+			return -ENOSPC;
+
+		stream->avail_out = dcur;
+		stream->next_out = walk.dst.virt.addr;
+
+		do {
+			int flush = Z_FINISH;
+			unsigned int scur;
+
+			stream->avail_in = 0;
+			stream->next_in = NULL;
+
+			scur = acomp_walk_next_src(&walk);
+			if (scur) {
+				if (acomp_walk_more_src(&walk, scur))
+					flush = Z_NO_FLUSH;
+				stream->avail_in = scur;
+				stream->next_in = walk.src.virt.addr;
+			}
+
+			ret = zlib_deflate(stream, flush);
+
+			if (scur) {
+				scur -= stream->avail_in;
+				acomp_walk_done_src(&walk, scur);
+			}
+		} while (ret == Z_OK && stream->avail_out);
+
+		acomp_walk_done_dst(&walk, dcur);
+	} while (ret == Z_OK);
+
+	if (ret != Z_STREAM_END)
+		return -EINVAL;
+
+	req->dlen = stream->total_out;
+	return 0;
+}
+
+static int deflate_compress(struct acomp_req *req)
+{
+	struct crypto_acomp_stream *s;
+	struct deflate_stream *ds;
+	int err;
+
+	s = crypto_acomp_lock_stream_bh(&deflate_streams);
+	ds = s->ctx;
+
+	err = zlib_deflateInit2(&ds->stream, DEFLATE_DEF_LEVEL, Z_DEFLATED,
+				-DEFLATE_DEF_WINBITS, DEFLATE_DEF_MEMLEVEL,
+				Z_DEFAULT_STRATEGY);
+	if (err != Z_OK) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	err = deflate_compress_one(req, ds);
+
+out:
+	crypto_acomp_unlock_stream_bh(s);
+
+	return err;
+}
+
+static int deflate_decompress_one(struct acomp_req *req,
+				  struct deflate_stream *ds)
+{
+	struct z_stream_s *stream = &ds->stream;
+	bool out_of_space = false;
+	struct acomp_walk walk;
+	int ret;
+
+	ret = acomp_walk_virt(&walk, req, true);
+	if (ret)
+		return ret;
+
+	do {
+		unsigned int scur;
+
+		stream->avail_in = 0;
+		stream->next_in = NULL;
+
+		scur = acomp_walk_next_src(&walk);
+		if (scur) {
+			stream->avail_in = scur;
+			stream->next_in = walk.src.virt.addr;
+		}
+
+		do {
+			unsigned int dcur;
+			unsigned long avail_in;
+
+			dcur = acomp_walk_next_dst(&walk);
+
+			stream->avail_out = dcur;
+			stream->next_out = walk.dst.virt.addr;
+			avail_in = stream->avail_in;
+
+			ret = zlib_inflate(stream, Z_NO_FLUSH);
+
+			if (!dcur && avail_in == stream->avail_in) {
+				out_of_space = true;
+				break;
+			}
+
+			dcur -= stream->avail_out;
+			acomp_walk_done_dst(&walk, dcur);
+		} while (ret == Z_OK && stream->avail_in);
+
+		if (scur)
+			acomp_walk_done_src(&walk, scur);
+
+		if (out_of_space)
+			return -ENOSPC;
+	} while (ret == Z_OK);
+
+	if (ret != Z_STREAM_END)
+		return -EINVAL;
+
+	req->dlen = stream->total_out;
+	return 0;
+}
+
+static int deflate_decompress(struct acomp_req *req)
+{
+	struct crypto_acomp_stream *s;
+	struct deflate_stream *ds;
+	int err;
+
+	s = crypto_acomp_lock_stream_bh(&deflate_streams);
+	ds = s->ctx;
+
+	err = zlib_inflateInit2(&ds->stream, -DEFLATE_DEF_WINBITS);
+	if (err != Z_OK) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	err = deflate_decompress_one(req, ds);
+
+out:
+	crypto_acomp_unlock_stream_bh(s);
+
+	return err;
+}
+
+static int deflate_init(struct crypto_acomp *tfm)
+{
+	int ret;
+
+	mutex_lock(&deflate_stream_lock);
+	ret = crypto_acomp_alloc_streams(&deflate_streams);
+	mutex_unlock(&deflate_stream_lock);
+
+	return ret;
+}
+
+static struct acomp_alg acomp = {
+	.compress		= deflate_compress,
+	.decompress		= deflate_decompress,
+	.init			= deflate_init,
+	.base.cra_name		= "deflate",
+	.base.cra_driver_name	= "deflate-generic",
+	.base.cra_flags		= CRYPTO_ALG_REQ_VIRT,
+	.base.cra_module	= THIS_MODULE,
+};
+
+static int __init deflate_mod_init(void)
+{
+	return crypto_register_acomp(&acomp);
+}
+
+static void __exit deflate_mod_fini(void)
+{
+	crypto_unregister_acomp(&acomp);
+	crypto_acomp_free_streams(&deflate_streams);
+}
+
+module_init(deflate_mod_init);
+module_exit(deflate_mod_fini);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Deflate Compression Algorithm for IPCOMP");
+MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
+MODULE_AUTHOR("Ard Biesheuvel <ardb@kernel.org>");
+MODULE_AUTHOR("Herbert Xu <herbert@gondor.apana.org.au>");
+MODULE_ALIAS_CRYPTO("deflate");
+MODULE_ALIAS_CRYPTO("deflate-generic");