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, 220 insertions, 0 deletions

diff --git a/fs/smb/server/compress.c b/fs/smb/server/compress.c
new file mode 100644
index 000000000..01d1771ff
--- /dev/null
+++ b/fs/smb/server/compress.c
@@ -0,0 +1,220 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * SMB2 compression support for ksmbd.
+ *
+ * Receive and send SMB 3.1.1 compression transforms using the common helpers.
+ *
+ * Copyright (C) 2026 Namjae Jeon <linkinjeon@kernel.org>
+ */
+#include <linux/slab.h>
+
+#include "compress.h"
+#include "smb_common.h"
+#include "../common/compress/lz77.h"
+
+#define SMB_COMPRESS_MIN_LEN	PAGE_SIZE
+
+/**
+ * ksmbd_decompress_request() - replace a compressed request with its SMB2 PDU
+ * @conn: connection which owns the current RFC1002 request buffer
+ *
+ * Derive the uncompressed size from the transform variant, enforce ksmbd's
+ * normal message limits, and ask the common decoder to validate every payload.
+ * On success, replace conn->request_buf with a regular RFC1002-framed SMB2
+ * message so the rest of the request path needs no compression awareness.
+ *
+ * Return: 0 on success, otherwise a negative errno.
+ */
+int ksmbd_decompress_request(struct ksmbd_conn *conn)
+{
+	struct smb2_compression_hdr *hdr;
+	unsigned int pdu_size = get_rfc1002_len(conn->request_buf);
+	u32 orig_size, offset, out_size;
+	u32 max_allowed_pdu_size;
+	char *buf, *out;
+	int rc;
+
+	if (pdu_size < sizeof(struct smb2_compression_hdr))
+		return -EINVAL;
+
+	if (conn->dialect != SMB311_PROT_ID ||
+	    conn->compress_algorithm == SMB3_COMPRESS_NONE)
+		return -EINVAL;
+
+	hdr = smb_get_msg(conn->request_buf);
+	if (hdr->ProtocolId != SMB2_COMPRESSION_TRANSFORM_ID)
+		return -EINVAL;
+
+	orig_size = le32_to_cpu(hdr->OriginalCompressedSegmentSize);
+	/*
+	 * For chained transforms the top-level header is only eight bytes; the
+	 * Flags field overlays the first payload header. Reject unknown Flags
+	 * and unnegotiated chained mode before allocating the output buffer.
+	 */
+	if (hdr->Flags == cpu_to_le16(SMB2_COMPRESSION_FLAG_CHAINED)) {
+		if (!conn->compress_chained)
+			return -EINVAL;
+		out_size = orig_size;
+	} else if (hdr->Flags == cpu_to_le16(SMB2_COMPRESSION_FLAG_NONE)) {
+		offset = le32_to_cpu(hdr->Offset);
+		if (offset > pdu_size - sizeof(*hdr) ||
+		    check_add_overflow(orig_size, offset, &out_size))
+			return -EINVAL;
+	} else {
+		return -EINVAL;
+	}
+
+	max_allowed_pdu_size = ksmbd_max_allowed_pdu_size(conn);
+	if (out_size < sizeof(struct smb2_pdu) ||
+	    out_size > max_allowed_pdu_size ||
+	    out_size > MAX_STREAM_PROT_LEN)
+		return -EINVAL;
+
+	out = kvmalloc(out_size + 4 + 1, KSMBD_DEFAULT_GFP);
+	if (!out)
+		return -ENOMEM;
+
+	buf = (char *)hdr;
+	*(__be32 *)out = cpu_to_be32(out_size);
+	rc = smb_compression_decompress(conn->compress_algorithm,
+					conn->compress_chained,
+					conn->compress_pattern,
+					buf, pdu_size, out + 4, out_size);
+	if (rc) {
+		kvfree(out);
+		return rc;
+	}
+
+	kvfree(conn->request_buf);
+	conn->request_buf = out;
+	return 0;
+}
+
+/**
+ * ksmbd_compress_response() - compress an eligible ksmbd response
+ * @work: request work item containing the response iov
+ *
+ * Compression transforms describe one contiguous SMB2 message, while ksmbd
+ * builds responses from multiple iov entries. Flatten the response first,
+ * produce the negotiated transform, and replace the response iov only when the
+ * result is smaller than the original message.
+ *
+ * Encrypted and compound responses are intentionally left unchanged. The
+ * caller may still continue sending the original response when this function
+ * returns zero.
+ *
+ * Return: 1 if the response was replaced, 0 if compression was skipped, or a
+ * negative errno on failure.
+ */
+int ksmbd_compress_response(struct ksmbd_work *work)
+{
+	struct smb2_compression_hdr *chdr;
+	struct smb2_hdr *req_hdr;
+	u32 src_len, dst_len, compressed_pdu_len, max_dst_len;
+	u8 *src = NULL, *out = NULL, *p;
+	int i, rc;
+
+	if (!work->compress_response || work->encrypted ||
+	    work->conn->compress_algorithm != SMB3_COMPRESS_LZ77)
+		return 0;
+
+	req_hdr = smb_get_msg(work->request_buf);
+	if (req_hdr->NextCommand || work->next_smb2_rcv_hdr_off ||
+	    work->next_smb2_rsp_hdr_off)
+		return 0;
+
+	src_len = get_rfc1002_len(work->iov[0].iov_base);
+	if (src_len < SMB_COMPRESS_MIN_LEN)
+		return 0;
+
+	src = kvmalloc(src_len, KSMBD_DEFAULT_GFP);
+	if (!src)
+		return -ENOMEM;
+
+	p = src;
+	/* iov[0] contains only the RFC1002 length; the SMB2 PDU starts at iov[1]. */
+	for (i = 1; i < work->iov_cnt; i++) {
+		if (work->iov[i].iov_len > src + src_len - p) {
+			rc = -EINVAL;
+			goto out;
+		}
+		memcpy(p, work->iov[i].iov_base, work->iov[i].iov_len);
+		p += work->iov[i].iov_len;
+	}
+	if (p != src + src_len) {
+		rc = -EINVAL;
+		goto out;
+	}
+
+	max_dst_len = smb_lz77_compressed_alloc_size(src_len) +
+		sizeof(struct smb2_compression_hdr) +
+		3 * sizeof(struct smb2_compression_payload_hdr) +
+		2 * sizeof(struct smb2_compression_pattern_v1);
+	out = kvzalloc(sizeof(__be32) + max_dst_len,
+		       KSMBD_DEFAULT_GFP);
+	if (!out) {
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	if (work->conn->compress_chained) {
+		dst_len = max_dst_len;
+		rc = smb_compression_compress_chained(SMB3_COMPRESS_LZ77,
+						      work->conn->compress_pattern,
+						      src, src_len,
+						      out + sizeof(__be32),
+						      &dst_len);
+		if (rc == -EMSGSIZE || dst_len >= src_len) {
+			rc = 0;
+			goto out;
+		}
+		if (rc)
+			goto out;
+		compressed_pdu_len = dst_len;
+	} else {
+		/*
+		 * Peers which did not negotiate chained compression still use
+		 * the original 16-byte unchained transform format.
+		 */
+		dst_len = smb_lz77_compressed_alloc_size(src_len);
+		rc = smb_lz77_compress(src, src_len,
+				       out + sizeof(__be32) + sizeof(*chdr),
+				       &dst_len);
+		if (rc == -EMSGSIZE ||
+		    dst_len + sizeof(*chdr) >= src_len) {
+			rc = 0;
+			goto out;
+		}
+		if (rc)
+			goto out;
+
+		compressed_pdu_len = sizeof(*chdr) + dst_len;
+		chdr = (struct smb2_compression_hdr *)(out + sizeof(__be32));
+		chdr->ProtocolId = SMB2_COMPRESSION_TRANSFORM_ID;
+		chdr->OriginalCompressedSegmentSize = cpu_to_le32(src_len);
+		chdr->CompressionAlgorithm = SMB3_COMPRESS_LZ77;
+		chdr->Flags = cpu_to_le16(SMB2_COMPRESSION_FLAG_NONE);
+		chdr->Offset = 0;
+	}
+
+	*(__be32 *)out = cpu_to_be32(compressed_pdu_len);
+
+	/*
+	 * Keep the transform in work->compress_buf until send completion.
+	 * Existing response iovs can then be replaced without changing their
+	 * individual ownership rules.
+	 */
+	work->compress_buf = out;
+	work->iov[0].iov_base = out;
+	work->iov[0].iov_len = sizeof(__be32);
+	work->iov[1].iov_base = out + sizeof(__be32);
+	work->iov[1].iov_len = compressed_pdu_len;
+	work->iov_cnt = 2;
+	work->iov_idx = 1;
+	out = NULL;
+	rc = 1;
+out:
+	kvfree(out);
+	kvfree(src);
+	return rc;
+}