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, 793 insertions, 0 deletions

diff --git a/fs/afs/vlclient.c b/fs/afs/vlclient.c
new file mode 100644
index 000000000..a40b43464
--- /dev/null
+++ b/fs/afs/vlclient.c
@@ -0,0 +1,793 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* AFS Volume Location Service client
+ *
+ * Copyright (C) 2002 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/gfp.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include "afs_fs.h"
+#include "internal.h"
+
+/*
+ * Deliver reply data to a VL.GetEntryByNameU call.
+ */
+static int afs_deliver_vl_get_entry_by_name_u(struct afs_call *call)
+{
+	struct afs_uvldbentry__xdr *uvldb;
+	struct afs_vldb_entry *entry;
+	u32 nr_servers, vlflags;
+	int i, ret;
+
+	_enter("");
+
+	ret = afs_transfer_reply(call);
+	if (ret < 0)
+		return ret;
+
+	/* unmarshall the reply once we've received all of it */
+	uvldb = call->buffer;
+	entry = call->ret_vldb;
+
+	nr_servers = ntohl(uvldb->nServers);
+	if (nr_servers > AFS_NMAXNSERVERS)
+		nr_servers = AFS_NMAXNSERVERS;
+
+	for (i = 0; i < ARRAY_SIZE(uvldb->name) - 1; i++)
+		entry->name[i] = (u8)ntohl(uvldb->name[i]);
+	entry->name[i] = 0;
+	entry->name_len = strlen(entry->name);
+
+	vlflags = ntohl(uvldb->flags);
+	for (i = 0; i < nr_servers; i++) {
+		struct afs_uuid__xdr *xdr;
+		struct afs_uuid *uuid;
+		u32 tmp = ntohl(uvldb->serverFlags[i]);
+		int j;
+		int n = entry->nr_servers;
+
+		if (tmp & AFS_VLSF_RWVOL) {
+			entry->fs_mask[n] |= AFS_VOL_VTM_RW;
+			if (vlflags & AFS_VLF_BACKEXISTS)
+				entry->fs_mask[n] |= AFS_VOL_VTM_BAK;
+		}
+		if (tmp & AFS_VLSF_ROVOL)
+			entry->fs_mask[n] |= AFS_VOL_VTM_RO;
+		if (!entry->fs_mask[n])
+			continue;
+
+		xdr = &uvldb->serverNumber[i];
+		uuid = (struct afs_uuid *)&entry->fs_server[n];
+		uuid->time_low			= xdr->time_low;
+		uuid->time_mid			= htons(ntohl(xdr->time_mid));
+		uuid->time_hi_and_version	= htons(ntohl(xdr->time_hi_and_version));
+		uuid->clock_seq_hi_and_reserved	= (u8)ntohl(xdr->clock_seq_hi_and_reserved);
+		uuid->clock_seq_low		= (u8)ntohl(xdr->clock_seq_low);
+		for (j = 0; j < 6; j++)
+			uuid->node[j] = (u8)ntohl(xdr->node[j]);
+
+		entry->vlsf_flags[n] = tmp;
+		entry->addr_version[n] = ntohl(uvldb->serverUnique[i]);
+		entry->nr_servers++;
+	}
+
+	for (i = 0; i < AFS_MAXTYPES; i++)
+		entry->vid[i] = ntohl(uvldb->volumeId[i]);
+
+	if (vlflags & AFS_VLF_RWEXISTS)
+		__set_bit(AFS_VLDB_HAS_RW, &entry->flags);
+	if (vlflags & AFS_VLF_ROEXISTS)
+		__set_bit(AFS_VLDB_HAS_RO, &entry->flags);
+	if (vlflags & AFS_VLF_BACKEXISTS)
+		__set_bit(AFS_VLDB_HAS_BAK, &entry->flags);
+
+	if (!(vlflags & (AFS_VLF_RWEXISTS | AFS_VLF_ROEXISTS | AFS_VLF_BACKEXISTS))) {
+		entry->error = -ENOMEDIUM;
+		__set_bit(AFS_VLDB_QUERY_ERROR, &entry->flags);
+	}
+
+	__set_bit(AFS_VLDB_QUERY_VALID, &entry->flags);
+	_leave(" = 0 [done]");
+	return 0;
+}
+
+/*
+ * VL.GetEntryByNameU operation type.
+ */
+static const struct afs_call_type afs_RXVLGetEntryByNameU = {
+	.name		= "VL.GetEntryByNameU",
+	.op		= afs_VL_GetEntryByNameU,
+	.deliver	= afs_deliver_vl_get_entry_by_name_u,
+	.destructor	= afs_flat_call_destructor,
+};
+
+/*
+ * Dispatch a get volume entry by name or ID operation (uuid variant).  If the
+ * volname is a decimal number then it's a volume ID not a volume name.
+ */
+struct afs_vldb_entry *afs_vl_get_entry_by_name_u(struct afs_vl_cursor *vc,
+						  const char *volname,
+						  int volnamesz)
+{
+	struct afs_vldb_entry *entry;
+	struct afs_call *call;
+	struct afs_net *net = vc->cell->net;
+	size_t reqsz, padsz;
+	__be32 *bp;
+
+	_enter("");
+
+	padsz = (4 - (volnamesz & 3)) & 3;
+	reqsz = 8 + volnamesz + padsz;
+
+	entry = kzalloc_obj(struct afs_vldb_entry);
+	if (!entry)
+		return ERR_PTR(-ENOMEM);
+
+	call = afs_alloc_flat_call(net, &afs_RXVLGetEntryByNameU, reqsz,
+				   sizeof(struct afs_uvldbentry__xdr));
+	if (!call) {
+		kfree(entry);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	call->key = vc->key;
+	call->ret_vldb = entry;
+	call->max_lifespan = AFS_VL_MAX_LIFESPAN;
+	call->peer = rxrpc_kernel_get_peer(vc->alist->addrs[vc->addr_index].peer);
+	call->service_id = vc->server->service_id;
+
+	/* Marshall the parameters */
+	bp = call->request;
+	*bp++ = htonl(VLGETENTRYBYNAMEU);
+	*bp++ = htonl(volnamesz);
+	memcpy(bp, volname, volnamesz);
+	if (padsz > 0)
+		memset((void *)bp + volnamesz, 0, padsz);
+
+	trace_afs_make_vl_call(call);
+	afs_make_call(call, GFP_KERNEL);
+	afs_wait_for_call_to_complete(call);
+	vc->call_abort_code	= call->abort_code;
+	vc->call_error		= call->error;
+	vc->call_responded	= call->responded;
+	afs_put_call(call);
+	if (vc->call_error) {
+		kfree(entry);
+		return ERR_PTR(vc->call_error);
+	}
+	return entry;
+}
+
+/*
+ * Deliver reply data to a VL.GetAddrsU call.
+ *
+ *	GetAddrsU(IN ListAddrByAttributes *inaddr,
+ *		  OUT afsUUID *uuidp1,
+ *		  OUT uint32_t *uniquifier,
+ *		  OUT uint32_t *nentries,
+ *		  OUT bulkaddrs *blkaddrs);
+ */
+static int afs_deliver_vl_get_addrs_u(struct afs_call *call)
+{
+	struct afs_addr_list *alist;
+	__be32 *bp;
+	u32 uniquifier, nentries, count;
+	int i, ret;
+
+	_enter("{%u,%zu/%u}",
+	       call->unmarshall, iov_iter_count(call->iter), call->count);
+
+	switch (call->unmarshall) {
+	case 0:
+		afs_extract_to_buf(call,
+				   sizeof(struct afs_uuid__xdr) + 3 * sizeof(__be32));
+		call->unmarshall++;
+
+		/* Extract the returned uuid, uniquifier, nentries and
+		 * blkaddrs size */
+		fallthrough;
+	case 1:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		bp = call->buffer + sizeof(struct afs_uuid__xdr);
+		uniquifier	= ntohl(*bp++);
+		nentries	= ntohl(*bp++);
+		count		= ntohl(*bp);
+
+		nentries = min(nentries, count);
+		alist = afs_alloc_addrlist(nentries);
+		if (!alist)
+			return -ENOMEM;
+		alist->version = uniquifier;
+		call->ret_alist = alist;
+		call->count = count;
+		call->count2 = nentries;
+		call->unmarshall++;
+
+	more_entries:
+		count = min(call->count, 4U);
+		afs_extract_to_buf(call, count * sizeof(__be32));
+
+		fallthrough;	/* and extract entries */
+	case 2:
+		ret = afs_extract_data(call, call->count > 4);
+		if (ret < 0)
+			return ret;
+
+		alist = call->ret_alist;
+		bp = call->buffer;
+		count = min(call->count, 4U);
+		for (i = 0; i < count; i++) {
+			if (alist->nr_addrs < call->count2) {
+				ret = afs_merge_fs_addr4(call->net, alist, *bp++, AFS_FS_PORT);
+				if (ret < 0)
+					return ret;
+			}
+		}
+
+		call->count -= count;
+		if (call->count > 0)
+			goto more_entries;
+		call->unmarshall++;
+		break;
+	}
+
+	_leave(" = 0 [done]");
+	return 0;
+}
+
+/*
+ * VL.GetAddrsU operation type.
+ */
+static const struct afs_call_type afs_RXVLGetAddrsU = {
+	.name		= "VL.GetAddrsU",
+	.op		= afs_VL_GetAddrsU,
+	.deliver	= afs_deliver_vl_get_addrs_u,
+	.destructor	= afs_flat_call_destructor,
+};
+
+/*
+ * Dispatch an operation to get the addresses for a server, where the server is
+ * nominated by UUID.
+ */
+struct afs_addr_list *afs_vl_get_addrs_u(struct afs_vl_cursor *vc,
+					 const uuid_t *uuid)
+{
+	struct afs_ListAddrByAttributes__xdr *r;
+	struct afs_addr_list *alist;
+	const struct afs_uuid *u = (const struct afs_uuid *)uuid;
+	struct afs_call *call;
+	struct afs_net *net = vc->cell->net;
+	__be32 *bp;
+	int i;
+
+	_enter("");
+
+	call = afs_alloc_flat_call(net, &afs_RXVLGetAddrsU,
+				   sizeof(__be32) + sizeof(struct afs_ListAddrByAttributes__xdr),
+				   sizeof(struct afs_uuid__xdr) + 3 * sizeof(__be32));
+	if (!call)
+		return ERR_PTR(-ENOMEM);
+
+	call->key = vc->key;
+	call->ret_alist = NULL;
+	call->max_lifespan = AFS_VL_MAX_LIFESPAN;
+	call->peer = rxrpc_kernel_get_peer(vc->alist->addrs[vc->addr_index].peer);
+	call->service_id = vc->server->service_id;
+
+	/* Marshall the parameters */
+	bp = call->request;
+	*bp++ = htonl(VLGETADDRSU);
+	r = (struct afs_ListAddrByAttributes__xdr *)bp;
+	r->Mask		= htonl(AFS_VLADDR_UUID);
+	r->ipaddr	= 0;
+	r->index	= 0;
+	r->spare	= 0;
+	r->uuid.time_low			= u->time_low;
+	r->uuid.time_mid			= htonl(ntohs(u->time_mid));
+	r->uuid.time_hi_and_version		= htonl(ntohs(u->time_hi_and_version));
+	r->uuid.clock_seq_hi_and_reserved 	= htonl(u->clock_seq_hi_and_reserved);
+	r->uuid.clock_seq_low			= htonl(u->clock_seq_low);
+	for (i = 0; i < 6; i++)
+		r->uuid.node[i] = htonl(u->node[i]);
+
+	trace_afs_make_vl_call(call);
+	afs_make_call(call, GFP_KERNEL);
+	afs_wait_for_call_to_complete(call);
+	vc->call_abort_code	= call->abort_code;
+	vc->call_error		= call->error;
+	vc->call_responded	= call->responded;
+	alist			= call->ret_alist;
+	afs_put_call(call);
+	if (vc->call_error) {
+		afs_put_addrlist(alist, afs_alist_trace_put_getaddru);
+		return ERR_PTR(vc->call_error);
+	}
+	return alist;
+}
+
+/*
+ * Deliver reply data to an VL.GetCapabilities operation.
+ */
+static int afs_deliver_vl_get_capabilities(struct afs_call *call)
+{
+	u32 count;
+	int ret;
+
+	_enter("{%u,%zu/%u}",
+	       call->unmarshall, iov_iter_count(call->iter), call->count);
+
+	switch (call->unmarshall) {
+	case 0:
+		afs_extract_to_tmp(call);
+		call->unmarshall++;
+
+		fallthrough;	/* and extract the capabilities word count */
+	case 1:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		count = ntohl(call->tmp);
+		call->count = count;
+		call->count2 = count;
+
+		call->unmarshall++;
+		afs_extract_discard(call, count * sizeof(__be32));
+
+		fallthrough;	/* and extract capabilities words */
+	case 2:
+		ret = afs_extract_data(call, false);
+		if (ret < 0)
+			return ret;
+
+		/* TODO: Examine capabilities */
+
+		call->unmarshall++;
+		break;
+	}
+
+	_leave(" = 0 [done]");
+	return 0;
+}
+
+static void afs_destroy_vl_get_capabilities(struct afs_call *call)
+{
+	afs_put_addrlist(call->vl_probe, afs_alist_trace_put_vlgetcaps);
+	afs_put_vlserver(call->net, call->vlserver);
+	afs_flat_call_destructor(call);
+}
+
+/*
+ * VL.GetCapabilities operation type
+ */
+static const struct afs_call_type afs_RXVLGetCapabilities = {
+	.name		= "VL.GetCapabilities",
+	.op		= afs_VL_GetCapabilities,
+	.deliver	= afs_deliver_vl_get_capabilities,
+	.immediate_cancel = afs_vlserver_probe_result,
+	.done		= afs_vlserver_probe_result,
+	.destructor	= afs_destroy_vl_get_capabilities,
+};
+
+/*
+ * Probe a volume server for the capabilities that it supports.  This can
+ * return up to 196 words.
+ *
+ * We use this to probe for service upgrade to determine what the server at the
+ * other end supports.
+ */
+struct afs_call *afs_vl_get_capabilities(struct afs_net *net,
+					 struct afs_addr_list *alist,
+					 unsigned int addr_index,
+					 struct key *key,
+					 struct afs_vlserver *server,
+					 unsigned int server_index)
+{
+	struct afs_call *call;
+	__be32 *bp;
+
+	_enter("");
+
+	call = afs_alloc_flat_call(net, &afs_RXVLGetCapabilities, 1 * 4, 16 * 4);
+	if (!call)
+		return ERR_PTR(-ENOMEM);
+
+	call->key = key;
+	call->vlserver = afs_get_vlserver(server);
+	call->server_index = server_index;
+	call->peer = rxrpc_kernel_get_peer(alist->addrs[addr_index].peer);
+	call->vl_probe = afs_get_addrlist(alist, afs_alist_trace_get_vlgetcaps);
+	call->probe_index = addr_index;
+	call->service_id = server->service_id;
+	call->upgrade = true;
+	call->async = true;
+	call->max_lifespan = AFS_PROBE_MAX_LIFESPAN;
+
+	/* marshall the parameters */
+	bp = call->request;
+	*bp++ = htonl(VLGETCAPABILITIES);
+
+	/* Can't take a ref on server */
+	trace_afs_make_vl_call(call);
+	afs_make_call(call, GFP_KERNEL);
+	return call;
+}
+
+/*
+ * Deliver reply data to a YFSVL.GetEndpoints call.
+ *
+ *	GetEndpoints(IN yfsServerAttributes *attr,
+ *		     OUT opr_uuid *uuid,
+ *		     OUT afs_int32 *uniquifier,
+ *		     OUT endpoints *fsEndpoints,
+ *		     OUT endpoints *volEndpoints)
+ */
+static int afs_deliver_yfsvl_get_endpoints(struct afs_call *call)
+{
+	struct afs_addr_list *alist;
+	__be32 *bp;
+	u32 uniquifier, size;
+	int ret;
+
+	_enter("{%u,%zu,%u}",
+	       call->unmarshall, iov_iter_count(call->iter), call->count2);
+
+	switch (call->unmarshall) {
+	case 0:
+		afs_extract_to_buf(call, sizeof(uuid_t) + 3 * sizeof(__be32));
+		call->unmarshall = 1;
+
+		/* Extract the returned uuid, uniquifier, fsEndpoints count and
+		 * either the first fsEndpoint type or the volEndpoints
+		 * count if there are no fsEndpoints. */
+		fallthrough;
+	case 1:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		bp = call->buffer + sizeof(uuid_t);
+		uniquifier	= ntohl(*bp++);
+		call->count	= ntohl(*bp++);
+		call->count2	= ntohl(*bp); /* Type or next count */
+
+		if (call->count > YFS_MAXENDPOINTS)
+			return afs_protocol_error(call, afs_eproto_yvl_fsendpt_num);
+
+		alist = afs_alloc_addrlist(call->count);
+		if (!alist)
+			return -ENOMEM;
+		alist->version = uniquifier;
+		call->ret_alist = alist;
+
+		if (call->count == 0)
+			goto extract_volendpoints;
+
+	next_fsendpoint:
+		switch (call->count2) {
+		case YFS_ENDPOINT_IPV4:
+			size = sizeof(__be32) * (1 + 1 + 1);
+			break;
+		case YFS_ENDPOINT_IPV6:
+			size = sizeof(__be32) * (1 + 4 + 1);
+			break;
+		default:
+			return afs_protocol_error(call, afs_eproto_yvl_fsendpt_type);
+		}
+
+		size += sizeof(__be32);
+		afs_extract_to_buf(call, size);
+		call->unmarshall = 2;
+
+		fallthrough;	/* and extract fsEndpoints[] entries */
+	case 2:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		alist = call->ret_alist;
+		bp = call->buffer;
+		switch (call->count2) {
+		case YFS_ENDPOINT_IPV4:
+			if (ntohl(bp[0]) != sizeof(__be32) * 2)
+				return afs_protocol_error(
+					call, afs_eproto_yvl_fsendpt4_len);
+			ret = afs_merge_fs_addr4(call->net, alist, bp[1], ntohl(bp[2]));
+			if (ret < 0)
+				return ret;
+			bp += 3;
+			break;
+		case YFS_ENDPOINT_IPV6:
+			if (ntohl(bp[0]) != sizeof(__be32) * 5)
+				return afs_protocol_error(
+					call, afs_eproto_yvl_fsendpt6_len);
+			ret = afs_merge_fs_addr6(call->net, alist, bp + 1, ntohl(bp[5]));
+			if (ret < 0)
+				return ret;
+			bp += 6;
+			break;
+		default:
+			return afs_protocol_error(call, afs_eproto_yvl_fsendpt_type);
+		}
+
+		/* Got either the type of the next entry or the count of
+		 * volEndpoints if no more fsEndpoints.
+		 */
+		call->count2 = ntohl(*bp++);
+
+		call->count--;
+		if (call->count > 0)
+			goto next_fsendpoint;
+
+	extract_volendpoints:
+		/* Extract the list of volEndpoints. */
+		call->count = call->count2;
+		if (!call->count)
+			goto end;
+		if (call->count > YFS_MAXENDPOINTS)
+			return afs_protocol_error(call, afs_eproto_yvl_vlendpt_type);
+
+		afs_extract_to_buf(call, 1 * sizeof(__be32));
+		call->unmarshall = 3;
+
+		/* Extract the type of volEndpoints[0].  Normally we would
+		 * extract the type of the next endpoint when we extract the
+		 * data of the current one, but this is the first...
+		 */
+		fallthrough;
+	case 3:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		bp = call->buffer;
+
+	next_volendpoint:
+		call->count2 = ntohl(*bp++);
+		switch (call->count2) {
+		case YFS_ENDPOINT_IPV4:
+			size = sizeof(__be32) * (1 + 1 + 1);
+			break;
+		case YFS_ENDPOINT_IPV6:
+			size = sizeof(__be32) * (1 + 4 + 1);
+			break;
+		default:
+			return afs_protocol_error(call, afs_eproto_yvl_vlendpt_type);
+		}
+
+		if (call->count > 1)
+			size += sizeof(__be32); /* Get next type too */
+		afs_extract_to_buf(call, size);
+		call->unmarshall = 4;
+
+		fallthrough;	/* and extract volEndpoints[] entries */
+	case 4:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		bp = call->buffer;
+		switch (call->count2) {
+		case YFS_ENDPOINT_IPV4:
+			if (ntohl(bp[0]) != sizeof(__be32) * 2)
+				return afs_protocol_error(
+					call, afs_eproto_yvl_vlendpt4_len);
+			bp += 3;
+			break;
+		case YFS_ENDPOINT_IPV6:
+			if (ntohl(bp[0]) != sizeof(__be32) * 5)
+				return afs_protocol_error(
+					call, afs_eproto_yvl_vlendpt6_len);
+			bp += 6;
+			break;
+		default:
+			return afs_protocol_error(call, afs_eproto_yvl_vlendpt_type);
+		}
+
+		/* Got either the type of the next entry or the count of
+		 * volEndpoints if no more fsEndpoints.
+		 */
+		call->count--;
+		if (call->count > 0)
+			goto next_volendpoint;
+
+	end:
+		afs_extract_discard(call, 0);
+		call->unmarshall = 5;
+
+		fallthrough;	/* Done */
+	case 5:
+		ret = afs_extract_data(call, false);
+		if (ret < 0)
+			return ret;
+		call->unmarshall = 6;
+		fallthrough;
+
+	case 6:
+		break;
+	}
+
+	_leave(" = 0 [done]");
+	return 0;
+}
+
+/*
+ * YFSVL.GetEndpoints operation type.
+ */
+static const struct afs_call_type afs_YFSVLGetEndpoints = {
+	.name		= "YFSVL.GetEndpoints",
+	.op		= afs_YFSVL_GetEndpoints,
+	.deliver	= afs_deliver_yfsvl_get_endpoints,
+	.destructor	= afs_flat_call_destructor,
+};
+
+/*
+ * Dispatch an operation to get the addresses for a server, where the server is
+ * nominated by UUID.
+ */
+struct afs_addr_list *afs_yfsvl_get_endpoints(struct afs_vl_cursor *vc,
+					      const uuid_t *uuid)
+{
+	struct afs_addr_list *alist;
+	struct afs_call *call;
+	struct afs_net *net = vc->cell->net;
+	__be32 *bp;
+
+	_enter("");
+
+	call = afs_alloc_flat_call(net, &afs_YFSVLGetEndpoints,
+				   sizeof(__be32) * 2 + sizeof(*uuid),
+				   sizeof(struct in6_addr) + sizeof(__be32) * 3);
+	if (!call)
+		return ERR_PTR(-ENOMEM);
+
+	call->key = vc->key;
+	call->ret_alist = NULL;
+	call->max_lifespan = AFS_VL_MAX_LIFESPAN;
+	call->peer = rxrpc_kernel_get_peer(vc->alist->addrs[vc->addr_index].peer);
+	call->service_id = vc->server->service_id;
+
+	/* Marshall the parameters */
+	bp = call->request;
+	*bp++ = htonl(YVLGETENDPOINTS);
+	*bp++ = htonl(YFS_SERVER_UUID);
+	memcpy(bp, uuid, sizeof(*uuid)); /* Type opr_uuid */
+
+	trace_afs_make_vl_call(call);
+	afs_make_call(call, GFP_KERNEL);
+	afs_wait_for_call_to_complete(call);
+	vc->call_abort_code	= call->abort_code;
+	vc->call_error		= call->error;
+	vc->call_responded	= call->responded;
+	alist			= call->ret_alist;
+	afs_put_call(call);
+	if (vc->call_error) {
+		afs_put_addrlist(alist, afs_alist_trace_put_getaddru);
+		return ERR_PTR(vc->call_error);
+	}
+	return alist;
+}
+
+/*
+ * Deliver reply data to a YFSVL.GetCellName operation.
+ */
+static int afs_deliver_yfsvl_get_cell_name(struct afs_call *call)
+{
+	char *cell_name;
+	u32 namesz, paddedsz;
+	int ret;
+
+	_enter("{%u,%zu/%u}",
+	       call->unmarshall, iov_iter_count(call->iter), call->count);
+
+	switch (call->unmarshall) {
+	case 0:
+		afs_extract_to_tmp(call);
+		call->unmarshall++;
+
+		fallthrough;	/* and extract the cell name length */
+	case 1:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		namesz = ntohl(call->tmp);
+		if (namesz > YFS_VL_MAXCELLNAME)
+			return afs_protocol_error(call, afs_eproto_cellname_len);
+		paddedsz = (namesz + 3) & ~3;
+		call->count = namesz;
+		call->count2 = paddedsz - namesz;
+
+		cell_name = kmalloc(namesz + 1, GFP_KERNEL);
+		if (!cell_name)
+			return -ENOMEM;
+		cell_name[namesz] = 0;
+		call->ret_str = cell_name;
+
+		afs_extract_begin(call, cell_name, namesz);
+		call->unmarshall++;
+
+		fallthrough;	/* and extract cell name */
+	case 2:
+		ret = afs_extract_data(call, true);
+		if (ret < 0)
+			return ret;
+
+		afs_extract_discard(call, call->count2);
+		call->unmarshall++;
+
+		fallthrough;	/* and extract padding */
+	case 3:
+		ret = afs_extract_data(call, false);
+		if (ret < 0)
+			return ret;
+
+		call->unmarshall++;
+		break;
+	}
+
+	_leave(" = 0 [done]");
+	return 0;
+}
+
+/*
+ * VL.GetCapabilities operation type
+ */
+static const struct afs_call_type afs_YFSVLGetCellName = {
+	.name		= "YFSVL.GetCellName",
+	.op		= afs_YFSVL_GetCellName,
+	.deliver	= afs_deliver_yfsvl_get_cell_name,
+	.destructor	= afs_flat_call_destructor,
+};
+
+/*
+ * Probe a volume server for the capabilities that it supports.  This can
+ * return up to 196 words.
+ *
+ * We use this to probe for service upgrade to determine what the server at the
+ * other end supports.
+ */
+char *afs_yfsvl_get_cell_name(struct afs_vl_cursor *vc)
+{
+	struct afs_call *call;
+	struct afs_net *net = vc->cell->net;
+	__be32 *bp;
+	char *cellname;
+
+	_enter("");
+
+	call = afs_alloc_flat_call(net, &afs_YFSVLGetCellName, 1 * 4, 0);
+	if (!call)
+		return ERR_PTR(-ENOMEM);
+
+	call->key = vc->key;
+	call->ret_str = NULL;
+	call->max_lifespan = AFS_VL_MAX_LIFESPAN;
+	call->peer = rxrpc_kernel_get_peer(vc->alist->addrs[vc->addr_index].peer);
+	call->service_id = vc->server->service_id;
+
+	/* marshall the parameters */
+	bp = call->request;
+	*bp++ = htonl(YVLGETCELLNAME);
+
+	/* Can't take a ref on server */
+	trace_afs_make_vl_call(call);
+	afs_make_call(call, GFP_KERNEL);
+	afs_wait_for_call_to_complete(call);
+	vc->call_abort_code	= call->abort_code;
+	vc->call_error		= call->error;
+	vc->call_responded	= call->responded;
+	cellname		= call->ret_str;
+	afs_put_call(call);
+	if (vc->call_error) {
+		kfree(cellname);
+		return ERR_PTR(vc->call_error);
+	}
+	return cellname;
+}