x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 598 insertions, 0 deletions

diff --git a/net/rds/message.c b/net/rds/message.c
new file mode 100644
index 000000000..47d5e9ab9
--- /dev/null
+++ b/net/rds/message.c
@@ -0,0 +1,598 @@
+/*
+ * Copyright (c) 2006, 2020 Oracle and/or its affiliates.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+#include <linux/skbuff.h>
+#include <linux/list.h>
+#include <linux/errqueue.h>
+
+#include "rds.h"
+
+static unsigned int	rds_exthdr_size[__RDS_EXTHDR_MAX] = {
+[RDS_EXTHDR_NONE]	= 0,
+[RDS_EXTHDR_VERSION]	= sizeof(struct rds_ext_header_version),
+[RDS_EXTHDR_RDMA]	= sizeof(struct rds_ext_header_rdma),
+[RDS_EXTHDR_RDMA_DEST]	= sizeof(struct rds_ext_header_rdma_dest),
+[RDS_EXTHDR_RDMA_BYTES] = sizeof(struct rds_ext_header_rdma_bytes),
+[RDS_EXTHDR_NPATHS]	= sizeof(__be16),
+[RDS_EXTHDR_GEN_NUM]	= sizeof(__be32),
+[RDS_EXTHDR_SPORT_IDX]	= 1,
+};
+
+void rds_message_addref(struct rds_message *rm)
+{
+	rdsdebug("addref rm %p ref %d\n", rm, refcount_read(&rm->m_refcount));
+	refcount_inc(&rm->m_refcount);
+}
+EXPORT_SYMBOL_GPL(rds_message_addref);
+
+static inline bool rds_zcookie_add(struct rds_msg_zcopy_info *info, u32 cookie)
+{
+	struct rds_zcopy_cookies *ck = &info->zcookies;
+	int ncookies = ck->num;
+
+	if (ncookies == RDS_MAX_ZCOOKIES)
+		return false;
+	ck->cookies[ncookies] = cookie;
+	ck->num =  ++ncookies;
+	return true;
+}
+
+static struct rds_msg_zcopy_info *rds_info_from_znotifier(struct rds_znotifier *znotif)
+{
+	return container_of(znotif, struct rds_msg_zcopy_info, znotif);
+}
+
+void rds_notify_msg_zcopy_purge(struct rds_msg_zcopy_queue *q)
+{
+	unsigned long flags;
+	LIST_HEAD(copy);
+	struct rds_msg_zcopy_info *info, *tmp;
+
+	spin_lock_irqsave(&q->lock, flags);
+	list_splice(&q->zcookie_head, &copy);
+	INIT_LIST_HEAD(&q->zcookie_head);
+	spin_unlock_irqrestore(&q->lock, flags);
+
+	list_for_each_entry_safe(info, tmp, &copy, rs_zcookie_next) {
+		list_del(&info->rs_zcookie_next);
+		kfree(info);
+	}
+}
+
+static void rds_rm_zerocopy_callback(struct rds_sock *rs,
+				     struct rds_znotifier *znotif)
+{
+	struct rds_msg_zcopy_info *info;
+	struct rds_msg_zcopy_queue *q;
+	u32 cookie = znotif->z_cookie;
+	struct rds_zcopy_cookies *ck;
+	struct list_head *head;
+	unsigned long flags;
+
+	mm_unaccount_pinned_pages(&znotif->z_mmp);
+	q = &rs->rs_zcookie_queue;
+	spin_lock_irqsave(&q->lock, flags);
+	head = &q->zcookie_head;
+	if (!list_empty(head)) {
+		info = list_first_entry(head, struct rds_msg_zcopy_info,
+					rs_zcookie_next);
+		if (rds_zcookie_add(info, cookie)) {
+			spin_unlock_irqrestore(&q->lock, flags);
+			kfree(rds_info_from_znotifier(znotif));
+			/* caller invokes rds_wake_sk_sleep() */
+			return;
+		}
+	}
+
+	info = rds_info_from_znotifier(znotif);
+	ck = &info->zcookies;
+	memset(ck, 0, sizeof(*ck));
+	WARN_ON(!rds_zcookie_add(info, cookie));
+	list_add_tail(&info->rs_zcookie_next, &q->zcookie_head);
+
+	spin_unlock_irqrestore(&q->lock, flags);
+	/* caller invokes rds_wake_sk_sleep() */
+}
+
+/*
+ * This relies on dma_map_sg() not touching sg[].page during merging.
+ */
+static void rds_message_purge(struct rds_message *rm)
+{
+	struct rds_znotifier *znotifier;
+	unsigned long i, flags;
+	bool zcopy;
+
+	if (unlikely(test_bit(RDS_MSG_PAGEVEC, &rm->m_flags)))
+		return;
+
+	spin_lock_irqsave(&rm->m_rs_lock, flags);
+	znotifier = rm->data.op_mmp_znotifier;
+	rm->data.op_mmp_znotifier = NULL;
+	zcopy = !!znotifier;
+
+	if (rm->m_rs) {
+		struct rds_sock *rs = rm->m_rs;
+
+		if (znotifier) {
+			rds_rm_zerocopy_callback(rs, znotifier);
+			rds_wake_sk_sleep(rs);
+		}
+		sock_put(rds_rs_to_sk(rs));
+		rm->m_rs = NULL;
+	} else if (znotifier) {
+		/*
+		 * Zerocopy can fail before the message is queued on the
+		 * socket, so there is no rs to carry the notification.
+		 */
+		mm_unaccount_pinned_pages(&znotifier->z_mmp);
+		kfree(rds_info_from_znotifier(znotifier));
+	}
+	spin_unlock_irqrestore(&rm->m_rs_lock, flags);
+
+	for (i = 0; i < rm->data.op_nents; i++) {
+		/* XXX will have to put_page for page refs */
+		if (!zcopy)
+			__free_page(sg_page(&rm->data.op_sg[i]));
+		else
+			put_page(sg_page(&rm->data.op_sg[i]));
+	}
+	rm->data.op_nents = 0;
+
+	if (rm->rdma.op_active)
+		rds_rdma_free_op(&rm->rdma);
+	if (rm->rdma.op_rdma_mr)
+		kref_put(&rm->rdma.op_rdma_mr->r_kref, __rds_put_mr_final);
+
+	if (rm->atomic.op_active)
+		rds_atomic_free_op(&rm->atomic);
+	if (rm->atomic.op_rdma_mr)
+		kref_put(&rm->atomic.op_rdma_mr->r_kref, __rds_put_mr_final);
+}
+
+static void rds_message_unpin_worker(struct work_struct *work)
+{
+	struct rds_message *rm = container_of(work, struct rds_message,
+					      m_unpin_work);
+
+	if (rm->rdma.op_unpin_deferred)
+		rds_rdma_op_unpin_pages(&rm->rdma);
+	if (rm->atomic.op_unpin_deferred)
+		rds_atomic_op_unpin_page(&rm->atomic);
+
+	kfree(rm);
+}
+
+void rds_message_put(struct rds_message *rm)
+{
+	rdsdebug("put rm %p ref %d\n", rm, refcount_read(&rm->m_refcount));
+	WARN(!refcount_read(&rm->m_refcount), "danger refcount zero on %p\n", rm);
+	if (refcount_dec_and_test(&rm->m_refcount)) {
+		BUG_ON(!list_empty(&rm->m_sock_item));
+		BUG_ON(!list_empty(&rm->m_conn_item));
+
+		rds_message_purge(rm);
+
+		/* A final put in atomic context cannot dirty the ops'
+		 * user pages on unpin, so rds_rdma_free_op() and
+		 * rds_atomic_free_op() deferred it.  Finish the unpin,
+		 * and the free, from process context.
+		 */
+		if (rm->rdma.op_unpin_deferred ||
+		    rm->atomic.op_unpin_deferred) {
+			INIT_WORK(&rm->m_unpin_work, rds_message_unpin_worker);
+			queue_work(rds_wq, &rm->m_unpin_work);
+			return;
+		}
+
+		kfree(rm);
+	}
+}
+EXPORT_SYMBOL_GPL(rds_message_put);
+
+void rds_message_populate_header(struct rds_header *hdr, __be16 sport,
+				 __be16 dport, u64 seq)
+{
+	hdr->h_flags = 0;
+	hdr->h_sport = sport;
+	hdr->h_dport = dport;
+	hdr->h_sequence = cpu_to_be64(seq);
+	/* see rds_find_next_ext_space for reason why we memset the
+	 * ext header
+	 */
+	memset(hdr->h_exthdr, RDS_EXTHDR_NONE, RDS_HEADER_EXT_SPACE);
+}
+EXPORT_SYMBOL_GPL(rds_message_populate_header);
+
+/*
+ * Find the next place we can add an RDS header extension with
+ * specific length. Extension headers are pushed one after the
+ * other. In the following, the number after the colon is the number
+ * of bytes:
+ *
+ * [ type1:1 dta1:len1 [ type2:1 dta2:len2 ] ... ] RDS_EXTHDR_NONE
+ *
+ * If the extension headers fill the complete extension header space
+ * (16 bytes), the trailing RDS_EXTHDR_NONE is omitted.
+ */
+static int rds_find_next_ext_space(struct rds_header *hdr, unsigned int len,
+				   u8 **ext_start)
+{
+	unsigned int ext_len;
+	unsigned int type;
+	int ind = 0;
+
+	while ((ind + 1 + len) <= RDS_HEADER_EXT_SPACE) {
+		if (hdr->h_exthdr[ind] == RDS_EXTHDR_NONE) {
+			*ext_start = hdr->h_exthdr + ind;
+			return 0;
+		}
+
+		type = hdr->h_exthdr[ind];
+
+		ext_len = (type < __RDS_EXTHDR_MAX) ? rds_exthdr_size[type] : 0;
+		WARN_ONCE(!ext_len, "Unknown ext hdr type %d\n", type);
+		if (!ext_len)
+			return -EINVAL;
+
+		/* ind points to a valid ext hdr with known length */
+		ind += 1 + ext_len;
+	}
+
+	/* no room for extension */
+	return -ENOSPC;
+}
+
+/* The ext hdr space is prefilled with zero from the kzalloc() */
+int rds_message_add_extension(struct rds_header *hdr,
+			      unsigned int type, const void *data)
+{
+	unsigned char *dst;
+	unsigned int len;
+
+	len = (type < __RDS_EXTHDR_MAX) ? rds_exthdr_size[type] : 0;
+	if (!len)
+		return 0;
+
+	if (rds_find_next_ext_space(hdr, len, &dst))
+		return 0;
+
+	*dst++ = type;
+	memcpy(dst, data, len);
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(rds_message_add_extension);
+
+/*
+ * If a message has extension headers, retrieve them here.
+ * Call like this:
+ *
+ * unsigned int pos = 0;
+ *
+ * while (1) {
+ *	buflen = sizeof(buffer);
+ *	type = rds_message_next_extension(hdr, &pos, buffer, &buflen);
+ *	if (type == RDS_EXTHDR_NONE)
+ *		break;
+ *	...
+ * }
+ */
+int rds_message_next_extension(struct rds_header *hdr,
+		unsigned int *pos, void *buf, unsigned int *buflen)
+{
+	unsigned int offset, ext_type, ext_len;
+	u8 *src = hdr->h_exthdr;
+
+	offset = *pos;
+	if (offset >= RDS_HEADER_EXT_SPACE)
+		goto none;
+
+	/* Get the extension type and length. For now, the
+	 * length is implied by the extension type. */
+	ext_type = src[offset++];
+
+	if (ext_type == RDS_EXTHDR_NONE || ext_type >= __RDS_EXTHDR_MAX)
+		goto none;
+	ext_len = rds_exthdr_size[ext_type];
+	if (offset + ext_len > RDS_HEADER_EXT_SPACE)
+		goto none;
+
+	*pos = offset + ext_len;
+	if (ext_len < *buflen)
+		*buflen = ext_len;
+	memcpy(buf, src + offset, *buflen);
+	return ext_type;
+
+none:
+	*pos = RDS_HEADER_EXT_SPACE;
+	*buflen = 0;
+	return RDS_EXTHDR_NONE;
+}
+
+int rds_message_add_rdma_dest_extension(struct rds_header *hdr, u32 r_key, u32 offset)
+{
+	struct rds_ext_header_rdma_dest ext_hdr;
+
+	ext_hdr.h_rdma_rkey = cpu_to_be32(r_key);
+	ext_hdr.h_rdma_offset = cpu_to_be32(offset);
+	return rds_message_add_extension(hdr, RDS_EXTHDR_RDMA_DEST, &ext_hdr);
+}
+EXPORT_SYMBOL_GPL(rds_message_add_rdma_dest_extension);
+
+/*
+ * Each rds_message is allocated with extra space for the scatterlist entries
+ * rds ops will need. This is to minimize memory allocation count. Then, each rds op
+ * can grab SGs when initializing its part of the rds_message.
+ */
+struct rds_message *rds_message_alloc(unsigned int extra_len, gfp_t gfp)
+{
+	struct rds_message *rm;
+
+	if (extra_len > KMALLOC_MAX_SIZE - sizeof(struct rds_message))
+		return NULL;
+
+	rm = kzalloc(sizeof(struct rds_message) + extra_len, gfp);
+	if (!rm)
+		goto out;
+
+	rm->m_used_sgs = 0;
+	rm->m_total_sgs = extra_len / sizeof(struct scatterlist);
+
+	refcount_set(&rm->m_refcount, 1);
+	INIT_LIST_HEAD(&rm->m_sock_item);
+	INIT_LIST_HEAD(&rm->m_conn_item);
+	spin_lock_init(&rm->m_rs_lock);
+	init_waitqueue_head(&rm->m_flush_wait);
+
+out:
+	return rm;
+}
+
+/*
+ * RDS ops use this to grab SG entries from the rm's sg pool.
+ */
+struct scatterlist *rds_message_alloc_sgs(struct rds_message *rm, int nents)
+{
+	struct scatterlist *sg_first = (struct scatterlist *) &rm[1];
+	struct scatterlist *sg_ret;
+
+	if (nents <= 0) {
+		pr_warn("rds: alloc sgs failed! nents <= 0\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (rm->m_used_sgs + nents > rm->m_total_sgs) {
+		pr_warn("rds: alloc sgs failed! total %d used %d nents %d\n",
+			rm->m_total_sgs, rm->m_used_sgs, nents);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	sg_ret = &sg_first[rm->m_used_sgs];
+	sg_init_table(sg_ret, nents);
+	rm->m_used_sgs += nents;
+
+	return sg_ret;
+}
+
+struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned int total_len)
+{
+	struct rds_message *rm;
+	unsigned int i;
+	int num_sgs = DIV_ROUND_UP(total_len, PAGE_SIZE);
+	int extra_bytes = num_sgs * sizeof(struct scatterlist);
+
+	rm = rds_message_alloc(extra_bytes, GFP_NOWAIT);
+	if (!rm)
+		return ERR_PTR(-ENOMEM);
+
+	set_bit(RDS_MSG_PAGEVEC, &rm->m_flags);
+	rm->m_inc.i_hdr.h_len = cpu_to_be32(total_len);
+	rm->data.op_nents = DIV_ROUND_UP(total_len, PAGE_SIZE);
+	rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs);
+	if (IS_ERR(rm->data.op_sg)) {
+		void *err = ERR_CAST(rm->data.op_sg);
+		rds_message_put(rm);
+		return err;
+	}
+
+	for (i = 0; i < rm->data.op_nents; ++i) {
+		sg_set_page(&rm->data.op_sg[i],
+				virt_to_page((void *)page_addrs[i]),
+				i == rm->data.op_nents - 1
+					? total_len - (i * PAGE_SIZE)
+					: PAGE_SIZE, 0);
+	}
+
+	return rm;
+}
+
+static int rds_message_zcopy_from_user(struct rds_message *rm, struct iov_iter *from)
+{
+	struct scatterlist *sg;
+	int ret = 0;
+	int length = iov_iter_count(from);
+	struct rds_msg_zcopy_info *info;
+
+	rm->m_inc.i_hdr.h_len = cpu_to_be32(iov_iter_count(from));
+
+	/*
+	 * now allocate and copy in the data payload.
+	 */
+	sg = rm->data.op_sg;
+
+	info = kzalloc_obj(*info);
+	if (!info)
+		return -ENOMEM;
+	INIT_LIST_HEAD(&info->rs_zcookie_next);
+	rm->data.op_mmp_znotifier = &info->znotif;
+	if (mm_account_pinned_pages(&rm->data.op_mmp_znotifier->z_mmp,
+				    length)) {
+		ret = -ENOMEM;
+		goto err;
+	}
+	while (iov_iter_count(from)) {
+		struct page *pages;
+		size_t start;
+		ssize_t copied;
+
+		copied = iov_iter_get_pages2(from, &pages, PAGE_SIZE,
+					    1, &start);
+		if (copied < 0) {
+			struct mmpin *mmp;
+			int i;
+
+			for (i = 0; i < rm->data.op_nents; i++)
+				put_page(sg_page(&rm->data.op_sg[i]));
+			rm->data.op_nents = 0;
+			mmp = &rm->data.op_mmp_znotifier->z_mmp;
+			mm_unaccount_pinned_pages(mmp);
+			ret = -EFAULT;
+			goto err;
+		}
+		length -= copied;
+		sg_set_page(sg, pages, copied, start);
+		rm->data.op_nents++;
+		sg++;
+	}
+	WARN_ON_ONCE(length != 0);
+	return ret;
+err:
+	kfree(info);
+	rm->data.op_mmp_znotifier = NULL;
+	return ret;
+}
+
+int rds_message_copy_from_user(struct rds_message *rm, struct iov_iter *from,
+			       bool zcopy)
+{
+	unsigned long to_copy, nbytes;
+	unsigned long sg_off;
+	struct scatterlist *sg;
+	int ret = 0;
+
+	rm->m_inc.i_hdr.h_len = cpu_to_be32(iov_iter_count(from));
+
+	/* now allocate and copy in the data payload.  */
+	sg = rm->data.op_sg;
+	sg_off = 0; /* Dear gcc, sg->page will be null from kzalloc. */
+
+	if (zcopy)
+		return rds_message_zcopy_from_user(rm, from);
+
+	while (iov_iter_count(from)) {
+		if (!sg_page(sg)) {
+			ret = rds_page_remainder_alloc(sg, iov_iter_count(from),
+						       GFP_HIGHUSER);
+			if (ret)
+				return ret;
+			rm->data.op_nents++;
+			sg_off = 0;
+		}
+
+		to_copy = min_t(unsigned long, iov_iter_count(from),
+				sg->length - sg_off);
+
+		rds_stats_add(s_copy_from_user, to_copy);
+		nbytes = copy_page_from_iter(sg_page(sg), sg->offset + sg_off,
+					     to_copy, from);
+		if (nbytes != to_copy)
+			return -EFAULT;
+
+		sg_off += to_copy;
+
+		if (sg_off == sg->length)
+			sg++;
+	}
+
+	return ret;
+}
+
+int rds_message_inc_copy_to_user(struct rds_incoming *inc, struct iov_iter *to)
+{
+	struct rds_message *rm;
+	struct scatterlist *sg;
+	unsigned long to_copy;
+	unsigned long vec_off;
+	int copied;
+	int ret;
+	u32 len;
+
+	rm = container_of(inc, struct rds_message, m_inc);
+	len = be32_to_cpu(rm->m_inc.i_hdr.h_len);
+
+	sg = rm->data.op_sg;
+	vec_off = 0;
+	copied = 0;
+
+	while (iov_iter_count(to) && copied < len) {
+		to_copy = min_t(unsigned long, iov_iter_count(to),
+				sg->length - vec_off);
+		to_copy = min_t(unsigned long, to_copy, len - copied);
+
+		rds_stats_add(s_copy_to_user, to_copy);
+		ret = copy_page_to_iter(sg_page(sg), sg->offset + vec_off,
+					to_copy, to);
+		if (ret != to_copy)
+			return -EFAULT;
+
+		vec_off += to_copy;
+		copied += to_copy;
+
+		if (vec_off == sg->length) {
+			vec_off = 0;
+			sg++;
+		}
+	}
+
+	return copied;
+}
+
+/*
+ * If the message is still on the send queue, wait until the transport
+ * is done with it. This is particularly important for RDMA operations.
+ */
+void rds_message_wait(struct rds_message *rm)
+{
+	wait_event_interruptible(rm->m_flush_wait,
+			!test_bit(RDS_MSG_MAPPED, &rm->m_flags));
+}
+
+void rds_message_unmapped(struct rds_message *rm)
+{
+	clear_bit(RDS_MSG_MAPPED, &rm->m_flags);
+	wake_up_interruptible(&rm->m_flush_wait);
+}
+EXPORT_SYMBOL_GPL(rds_message_unmapped);