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, 895 insertions, 0 deletions

diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
new file mode 100644
index 000000000..cbd26da44
--- /dev/null
+++ b/net/rxrpc/key.c
@@ -0,0 +1,895 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* RxRPC key management
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * RxRPC keys should have a description of describing their purpose:
+ *	"afs@example.com"
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/net.h>
+#include <linux/overflow.h>
+#include <linux/skbuff.h>
+#include <linux/key-type.h>
+#include <linux/ctype.h>
+#include <linux/slab.h>
+#include <net/sock.h>
+#include <net/af_rxrpc.h>
+#include <keys/rxrpc-type.h>
+#include <keys/user-type.h>
+#include "ar-internal.h"
+
+static int rxrpc_preparse(struct key_preparsed_payload *);
+static void rxrpc_free_preparse(struct key_preparsed_payload *);
+static void rxrpc_destroy(struct key *);
+static void rxrpc_describe(const struct key *, struct seq_file *);
+static long rxrpc_read(const struct key *, char *, size_t);
+
+/*
+ * rxrpc defined keys take an arbitrary string as the description and an
+ * arbitrary blob of data as the payload
+ */
+struct key_type key_type_rxrpc = {
+	.name		= "rxrpc",
+	.flags		= KEY_TYPE_NET_DOMAIN,
+	.preparse	= rxrpc_preparse,
+	.free_preparse	= rxrpc_free_preparse,
+	.instantiate	= generic_key_instantiate,
+	.destroy	= rxrpc_destroy,
+	.describe	= rxrpc_describe,
+	.read		= rxrpc_read,
+};
+EXPORT_SYMBOL(key_type_rxrpc);
+
+/*
+ * parse an RxKAD type XDR format token
+ * - the caller guarantees we have at least 4 words
+ */
+static int rxrpc_preparse_xdr_rxkad(struct key_preparsed_payload *prep,
+				    size_t datalen,
+				    const __be32 *xdr, unsigned int toklen)
+{
+	struct rxrpc_key_token *token, **pptoken;
+	time64_t expiry;
+	size_t plen;
+	u32 tktlen;
+
+	_enter(",{%x,%x,%x,%x},%u",
+	       ntohl(xdr[0]), ntohl(xdr[1]), ntohl(xdr[2]), ntohl(xdr[3]),
+	       toklen);
+
+	if (toklen <= 8 * 4)
+		return -EKEYREJECTED;
+	tktlen = ntohl(xdr[7]);
+	_debug("tktlen: %x", tktlen);
+	if (tktlen > AFSTOKEN_RK_TIX_MAX)
+		return -EKEYREJECTED;
+	if (toklen < 8 * 4 + tktlen)
+		return -EKEYREJECTED;
+
+	plen = sizeof(*token) + sizeof(*token->kad) + tktlen;
+	prep->quotalen += datalen + plen;
+
+	plen -= sizeof(*token);
+	token = kzalloc_obj(*token);
+	if (!token)
+		return -ENOMEM;
+
+	token->kad = kzalloc(plen, GFP_KERNEL);
+	if (!token->kad) {
+		kfree(token);
+		return -ENOMEM;
+	}
+
+	token->security_index	= RXRPC_SECURITY_RXKAD;
+	token->kad->ticket_len	= tktlen;
+	token->kad->vice_id	= ntohl(xdr[0]);
+	token->kad->kvno	= ntohl(xdr[1]);
+	token->kad->start	= ntohl(xdr[4]);
+	token->kad->expiry	= ntohl(xdr[5]);
+	token->kad->primary_flag = ntohl(xdr[6]);
+	memcpy(&token->kad->session_key, &xdr[2], 8);
+	memcpy(&token->kad->ticket, &xdr[8], tktlen);
+
+	_debug("SCIX: %u", token->security_index);
+	_debug("TLEN: %u", token->kad->ticket_len);
+	_debug("EXPY: %x", token->kad->expiry);
+	_debug("KVNO: %u", token->kad->kvno);
+	_debug("PRIM: %u", token->kad->primary_flag);
+	_debug("SKEY: %02x%02x%02x%02x%02x%02x%02x%02x",
+	       token->kad->session_key[0], token->kad->session_key[1],
+	       token->kad->session_key[2], token->kad->session_key[3],
+	       token->kad->session_key[4], token->kad->session_key[5],
+	       token->kad->session_key[6], token->kad->session_key[7]);
+	if (token->kad->ticket_len >= 8)
+		_debug("TCKT: %02x%02x%02x%02x%02x%02x%02x%02x",
+		       token->kad->ticket[0], token->kad->ticket[1],
+		       token->kad->ticket[2], token->kad->ticket[3],
+		       token->kad->ticket[4], token->kad->ticket[5],
+		       token->kad->ticket[6], token->kad->ticket[7]);
+
+	/* count the number of tokens attached */
+	prep->payload.data[1] = (void *)((unsigned long)prep->payload.data[1] + 1);
+
+	/* attach the data */
+	for (pptoken = (struct rxrpc_key_token **)&prep->payload.data[0];
+	     *pptoken;
+	     pptoken = &(*pptoken)->next)
+		continue;
+	*pptoken = token;
+	expiry = rxrpc_u32_to_time64(token->kad->expiry);
+	if (expiry < prep->expiry)
+		prep->expiry = expiry;
+
+	_leave(" = 0");
+	return 0;
+}
+
+static u64 xdr_dec64(const __be32 *xdr)
+{
+	return (u64)ntohl(xdr[0]) << 32 | (u64)ntohl(xdr[1]);
+}
+
+static time64_t rxrpc_s64_to_time64(s64 time_in_100ns)
+{
+	bool neg = false;
+	u64 tmp = time_in_100ns;
+
+	if (time_in_100ns < 0) {
+		tmp = -time_in_100ns;
+		neg = true;
+	}
+	do_div(tmp, 10000000);
+	return neg ? -tmp : tmp;
+}
+
+/*
+ * Parse a YFS-RxGK type XDR format token
+ * - the caller guarantees we have at least 4 words
+ *
+ * struct token_rxgk {
+ *	opr_time begintime;
+ *	opr_time endtime;
+ *	afs_int64 level;
+ *	afs_int64 lifetime;
+ *	afs_int64 bytelife;
+ *	afs_int64 enctype;
+ *	opaque key<>;
+ *	opaque ticket<>;
+ * };
+ */
+static int rxrpc_preparse_xdr_yfs_rxgk(struct key_preparsed_payload *prep,
+				       size_t datalen,
+				       const __be32 *xdr, unsigned int toklen)
+{
+	struct rxrpc_key_token *token, **pptoken;
+	time64_t expiry;
+	size_t plen;
+	const __be32 *ticket, *key;
+	s64 tmp;
+	size_t raw_keylen, raw_tktlen, keylen, tktlen;
+
+	_enter(",{%x,%x,%x,%x},%x",
+	       ntohl(xdr[0]), ntohl(xdr[1]), ntohl(xdr[2]), ntohl(xdr[3]),
+	       toklen);
+
+	if (6 * 2 + 2 > toklen / 4)
+		goto reject;
+
+	key = xdr + (6 * 2 + 1);
+	raw_keylen = ntohl(key[-1]);
+	_debug("keylen: %zx", raw_keylen);
+	if (raw_keylen > AFSTOKEN_GK_KEY_MAX)
+		goto reject;
+	keylen = round_up(raw_keylen, 4);
+	if ((6 * 2 + 2) * 4 + keylen > toklen)
+		goto reject;
+
+	ticket = xdr + (6 * 2 + 1 + (keylen / 4) + 1);
+	raw_tktlen = ntohl(ticket[-1]);
+	_debug("tktlen: %zx", raw_tktlen);
+	if (raw_tktlen > AFSTOKEN_GK_TOKEN_MAX)
+		goto reject;
+	tktlen = round_up(raw_tktlen, 4);
+	if ((6 * 2 + 2) * 4 + keylen + tktlen != toklen) {
+		kleave(" = -EKEYREJECTED [%zx!=%x, %zx,%zx]",
+		       (6 * 2 + 2) * 4 + keylen + tktlen, toklen,
+		       keylen, tktlen);
+		goto reject;
+	}
+
+	plen = sizeof(*token) + sizeof(*token->rxgk) + tktlen + keylen;
+	prep->quotalen += datalen + plen;
+
+	plen -= sizeof(*token);
+	token = kzalloc_obj(*token);
+	if (!token)
+		goto nomem;
+
+	token->rxgk = kzalloc_flex(struct rxgk_key, _key, raw_keylen);
+	if (!token->rxgk)
+		goto nomem_token;
+
+	token->security_index	= RXRPC_SECURITY_YFS_RXGK;
+	token->rxgk->begintime	= xdr_dec64(xdr + 0 * 2);
+	token->rxgk->endtime	= xdr_dec64(xdr + 1 * 2);
+	token->rxgk->level	= tmp = xdr_dec64(xdr + 2 * 2);
+	if (tmp < -1LL || tmp > RXRPC_SECURITY_ENCRYPT)
+		goto reject_token;
+	token->rxgk->lifetime	= xdr_dec64(xdr + 3 * 2);
+	token->rxgk->bytelife	= xdr_dec64(xdr + 4 * 2);
+	token->rxgk->enctype	= tmp = xdr_dec64(xdr + 5 * 2);
+	if (tmp < 0 || tmp > UINT_MAX)
+		goto reject_token;
+	token->rxgk->key.len	= raw_keylen;
+	token->rxgk->key.data	= token->rxgk->_key;
+	token->rxgk->ticket.len = raw_tktlen;
+
+	if (token->rxgk->endtime != 0) {
+		expiry = rxrpc_s64_to_time64(token->rxgk->endtime);
+		if (expiry < 0)
+			goto expired;
+		if (expiry < prep->expiry)
+			prep->expiry = expiry;
+	}
+
+	memcpy(token->rxgk->key.data, key, token->rxgk->key.len);
+
+	/* Pad the ticket so that we can use it directly in XDR */
+	token->rxgk->ticket.data = kzalloc(tktlen, GFP_KERNEL);
+	if (!token->rxgk->ticket.data)
+		goto nomem_yrxgk;
+	memcpy(token->rxgk->ticket.data, ticket, token->rxgk->ticket.len);
+
+	_debug("SCIX: %u",	token->security_index);
+	_debug("EXPY: %llx",	token->rxgk->endtime);
+	_debug("LIFE: %llx",	token->rxgk->lifetime);
+	_debug("BYTE: %llx",	token->rxgk->bytelife);
+	_debug("ENC : %u",	token->rxgk->enctype);
+	_debug("LEVL: %u",	token->rxgk->level);
+	_debug("KLEN: %u",	token->rxgk->key.len);
+	_debug("TLEN: %u",	token->rxgk->ticket.len);
+	_debug("KEY0: %*phN",	token->rxgk->key.len, token->rxgk->key.data);
+	_debug("TICK: %*phN",
+	       min_t(u32, token->rxgk->ticket.len, 32), token->rxgk->ticket.data);
+
+	/* count the number of tokens attached */
+	prep->payload.data[1] = (void *)((unsigned long)prep->payload.data[1] + 1);
+
+	/* attach the data */
+	for (pptoken = (struct rxrpc_key_token **)&prep->payload.data[0];
+	     *pptoken;
+	     pptoken = &(*pptoken)->next)
+		continue;
+	*pptoken = token;
+
+	_leave(" = 0");
+	return 0;
+
+nomem_yrxgk:
+	kfree(token->rxgk);
+nomem_token:
+	kfree(token);
+nomem:
+	return -ENOMEM;
+reject_token:
+	kfree(token->rxgk);
+	kfree(token);
+reject:
+	return -EKEYREJECTED;
+expired:
+	kfree(token->rxgk);
+	kfree(token);
+	return -EKEYEXPIRED;
+}
+
+/*
+ * attempt to parse the data as the XDR format
+ * - the caller guarantees we have more than 7 words
+ */
+static int rxrpc_preparse_xdr(struct key_preparsed_payload *prep)
+{
+	const __be32 *xdr = prep->data, *token, *p;
+	const char *cp;
+	unsigned int len, paddedlen, loop, ntoken, toklen, sec_ix;
+	size_t datalen = prep->datalen;
+	int ret, ret2;
+
+	_enter(",{%x,%x,%x,%x},%zu",
+	       ntohl(xdr[0]), ntohl(xdr[1]), ntohl(xdr[2]), ntohl(xdr[3]),
+	       prep->datalen);
+
+	if (datalen > AFSTOKEN_LENGTH_MAX)
+		goto not_xdr;
+
+	/* XDR is an array of __be32's */
+	if (datalen & 3)
+		goto not_xdr;
+
+	/* the flags should be 0 (the setpag bit must be handled by
+	 * userspace) */
+	if (ntohl(*xdr++) != 0)
+		goto not_xdr;
+	datalen -= 4;
+
+	/* check the cell name */
+	len = ntohl(*xdr++);
+	if (len < 1 || len > AFSTOKEN_CELL_MAX)
+		goto not_xdr;
+	datalen -= 4;
+	paddedlen = (len + 3) & ~3;
+	if (paddedlen > datalen)
+		goto not_xdr;
+
+	cp = (const char *) xdr;
+	for (loop = 0; loop < len; loop++)
+		if (!isprint(cp[loop]))
+			goto not_xdr;
+	for (; loop < paddedlen; loop++)
+		if (cp[loop])
+			goto not_xdr;
+	_debug("cellname: [%u/%u] '%*.*s'",
+	       len, paddedlen, len, len, (const char *) xdr);
+	datalen -= paddedlen;
+	xdr += paddedlen >> 2;
+
+	/* get the token count */
+	if (datalen < 12)
+		goto not_xdr;
+	ntoken = ntohl(*xdr++);
+	datalen -= 4;
+	_debug("ntoken: %x", ntoken);
+	if (ntoken < 1 || ntoken > AFSTOKEN_MAX)
+		goto not_xdr;
+
+	/* check each token wrapper */
+	p = xdr;
+	loop = ntoken;
+	do {
+		if (datalen < 8)
+			goto not_xdr;
+		toklen = ntohl(*p++);
+		sec_ix = ntohl(*p);
+		datalen -= 4;
+		_debug("token: [%x/%zx] %x", toklen, datalen, sec_ix);
+		paddedlen = (toklen + 3) & ~3;
+		if (toklen < 20 || toklen > datalen || paddedlen > datalen)
+			goto not_xdr;
+		datalen -= paddedlen;
+		p += paddedlen >> 2;
+
+	} while (--loop > 0);
+
+	_debug("remainder: %zu", datalen);
+	if (datalen != 0)
+		goto not_xdr;
+
+	/* okay: we're going to assume it's valid XDR format
+	 * - we ignore the cellname, relying on the key to be correctly named
+	 */
+	ret = -EPROTONOSUPPORT;
+	do {
+		toklen = ntohl(*xdr++);
+		token = xdr;
+		xdr += (toklen + 3) / 4;
+
+		sec_ix = ntohl(*token++);
+		toklen -= 4;
+
+		_debug("TOKEN type=%x len=%x", sec_ix, toklen);
+
+		switch (sec_ix) {
+		case RXRPC_SECURITY_RXKAD:
+			ret2 = rxrpc_preparse_xdr_rxkad(prep, datalen, token, toklen);
+			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			ret2 = rxrpc_preparse_xdr_yfs_rxgk(prep, datalen, token, toklen);
+			break;
+		default:
+			ret2 = -EPROTONOSUPPORT;
+			break;
+		}
+
+		switch (ret2) {
+		case 0:
+			ret = 0;
+			break;
+		case -EPROTONOSUPPORT:
+			break;
+		case -ENOPKG:
+			if (ret != 0)
+				ret = -ENOPKG;
+			break;
+		default:
+			ret = ret2;
+			goto error;
+		}
+
+	} while (--ntoken > 0);
+
+error:
+	_leave(" = %d", ret);
+	return ret;
+
+not_xdr:
+	_leave(" = -EPROTO");
+	return -EPROTO;
+}
+
+/*
+ * Preparse an rxrpc defined key.
+ *
+ * Data should be of the form:
+ *	OFFSET	LEN	CONTENT
+ *	0	4	key interface version number
+ *	4	2	security index (type)
+ *	6	2	ticket length
+ *	8	4	key expiry time (time_t)
+ *	12	4	kvno
+ *	16	8	session key
+ *	24	[len]	ticket
+ *
+ * if no data is provided, then a no-security key is made
+ */
+static int rxrpc_preparse(struct key_preparsed_payload *prep)
+{
+	const struct rxrpc_key_data_v1 *v1;
+	struct rxrpc_key_token *token, **pp;
+	time64_t expiry;
+	size_t plen;
+	u32 kver;
+	int ret;
+
+	_enter("%zu", prep->datalen);
+
+	/* handle a no-security key */
+	if (!prep->data && prep->datalen == 0)
+		return 0;
+
+	/* determine if the XDR payload format is being used */
+	if (prep->datalen > 7 * 4) {
+		ret = rxrpc_preparse_xdr(prep);
+		if (ret != -EPROTO)
+			return ret;
+	}
+
+	/* get the key interface version number */
+	ret = -EINVAL;
+	if (prep->datalen <= 4 || !prep->data)
+		goto error;
+	memcpy(&kver, prep->data, sizeof(kver));
+	prep->data += sizeof(kver);
+	prep->datalen -= sizeof(kver);
+	prep->quotalen = 0;
+
+	_debug("KEY I/F VERSION: %u", kver);
+
+	ret = -EKEYREJECTED;
+	if (kver != 1)
+		goto error;
+
+	/* deal with a version 1 key */
+	ret = -EINVAL;
+	if (prep->datalen < sizeof(*v1))
+		goto error;
+
+	v1 = prep->data;
+	if (prep->datalen != sizeof(*v1) + v1->ticket_length)
+		goto error;
+
+	_debug("SCIX: %u", v1->security_index);
+	_debug("TLEN: %u", v1->ticket_length);
+	_debug("EXPY: %x", v1->expiry);
+	_debug("KVNO: %u", v1->kvno);
+	_debug("SKEY: %02x%02x%02x%02x%02x%02x%02x%02x",
+	       v1->session_key[0], v1->session_key[1],
+	       v1->session_key[2], v1->session_key[3],
+	       v1->session_key[4], v1->session_key[5],
+	       v1->session_key[6], v1->session_key[7]);
+	if (v1->ticket_length >= 8)
+		_debug("TCKT: %02x%02x%02x%02x%02x%02x%02x%02x",
+		       v1->ticket[0], v1->ticket[1],
+		       v1->ticket[2], v1->ticket[3],
+		       v1->ticket[4], v1->ticket[5],
+		       v1->ticket[6], v1->ticket[7]);
+
+	ret = -EPROTONOSUPPORT;
+	if (v1->security_index != RXRPC_SECURITY_RXKAD)
+		goto error;
+
+	ret = -EKEYREJECTED;
+	if (v1->ticket_length > AFSTOKEN_RK_TIX_MAX)
+		goto error;
+
+	plen = sizeof(*token->kad) + v1->ticket_length;
+	prep->quotalen += plen + sizeof(*token);
+
+	ret = -ENOMEM;
+	token = kzalloc_obj(*token);
+	if (!token)
+		goto error;
+	token->kad = kzalloc(plen, GFP_KERNEL);
+	if (!token->kad)
+		goto error_free;
+
+	token->security_index		= RXRPC_SECURITY_RXKAD;
+	token->kad->ticket_len		= v1->ticket_length;
+	token->kad->expiry		= v1->expiry;
+	token->kad->kvno		= v1->kvno;
+	memcpy(&token->kad->session_key, &v1->session_key, 8);
+	memcpy(&token->kad->ticket, v1->ticket, v1->ticket_length);
+
+	/* count the number of tokens attached */
+	prep->payload.data[1] = (void *)((unsigned long)prep->payload.data[1] + 1);
+
+	/* attach the data */
+	pp = (struct rxrpc_key_token **)&prep->payload.data[0];
+	while (*pp)
+		pp = &(*pp)->next;
+	*pp = token;
+	expiry = rxrpc_u32_to_time64(token->kad->expiry);
+	if (expiry < prep->expiry)
+		prep->expiry = expiry;
+	token = NULL;
+	ret = 0;
+
+error_free:
+	kfree(token);
+error:
+	return ret;
+}
+
+/*
+ * Free token list.
+ */
+static void rxrpc_free_token_list(struct rxrpc_key_token *token)
+{
+	struct rxrpc_key_token *next;
+
+	for (; token; token = next) {
+		next = token->next;
+		switch (token->security_index) {
+		case RXRPC_SECURITY_RXKAD:
+			kfree(token->kad);
+			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			kfree(token->rxgk->ticket.data);
+			kfree(token->rxgk);
+			break;
+		default:
+			pr_err("Unknown token type %x on rxrpc key\n",
+			       token->security_index);
+			BUG();
+		}
+
+		kfree(token);
+	}
+}
+
+/*
+ * Clean up preparse data.
+ */
+static void rxrpc_free_preparse(struct key_preparsed_payload *prep)
+{
+	rxrpc_free_token_list(prep->payload.data[0]);
+}
+
+/*
+ * dispose of the data dangling from the corpse of a rxrpc key
+ */
+static void rxrpc_destroy(struct key *key)
+{
+	rxrpc_free_token_list(key->payload.data[0]);
+}
+
+/*
+ * describe the rxrpc key
+ */
+static void rxrpc_describe(const struct key *key, struct seq_file *m)
+{
+	const struct rxrpc_key_token *token;
+	const char *sep = ": ";
+
+	seq_puts(m, key->description);
+
+	for (token = key->payload.data[0]; token; token = token->next) {
+		seq_puts(m, sep);
+
+		switch (token->security_index) {
+		case RXRPC_SECURITY_RXKAD:
+			seq_puts(m, "ka");
+			break;
+		case RXRPC_SECURITY_YFS_RXGK:
+			seq_puts(m, "ygk");
+			break;
+		default: /* we have a ticket we can't encode */
+			seq_printf(m, "%u", token->security_index);
+			break;
+		}
+
+		sep = " ";
+	}
+}
+
+/*
+ * grab the security key for a socket
+ */
+int rxrpc_request_key(struct rxrpc_sock *rx, sockptr_t optval, int optlen)
+{
+	struct key *key;
+	char *description;
+
+	_enter("");
+
+	if (optlen <= 0 || optlen > PAGE_SIZE - 1 || rx->key)
+		return -EINVAL;
+
+	description = memdup_sockptr_nul(optval, optlen);
+	if (IS_ERR(description))
+		return PTR_ERR(description);
+
+	key = request_key_net(&key_type_rxrpc, description, sock_net(&rx->sk), NULL);
+	if (IS_ERR(key)) {
+		kfree(description);
+		_leave(" = %ld", PTR_ERR(key));
+		return PTR_ERR(key);
+	}
+
+	rx->key = key;
+	kfree(description);
+	_leave(" = 0 [key %x]", key->serial);
+	return 0;
+}
+
+/*
+ * generate a server data key
+ */
+int rxrpc_get_server_data_key(struct rxrpc_connection *conn,
+			      const void *session_key,
+			      time64_t expiry,
+			      u32 kvno)
+{
+	const struct cred *cred = current_cred();
+	struct key *key;
+	int ret;
+
+	struct {
+		u32 kver;
+		struct rxrpc_key_data_v1 v1;
+	} data;
+
+	_enter("");
+
+	key = key_alloc(&key_type_rxrpc, "x",
+			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, 0,
+			KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (IS_ERR(key)) {
+		_leave(" = -ENOMEM [alloc %ld]", PTR_ERR(key));
+		return -ENOMEM;
+	}
+
+	_debug("key %d", key_serial(key));
+
+	data.kver = 1;
+	data.v1.security_index = RXRPC_SECURITY_RXKAD;
+	data.v1.ticket_length = 0;
+	data.v1.expiry = rxrpc_time64_to_u32(expiry);
+	data.v1.kvno = 0;
+
+	memcpy(&data.v1.session_key, session_key, sizeof(data.v1.session_key));
+
+	ret = key_instantiate_and_link(key, &data, sizeof(data), NULL, NULL);
+	if (ret < 0)
+		goto error;
+
+	conn->key = key;
+	_leave(" = 0 [%d]", key_serial(key));
+	return 0;
+
+error:
+	key_revoke(key);
+	key_put(key);
+	_leave(" = -ENOMEM [ins %d]", ret);
+	return -ENOMEM;
+}
+EXPORT_SYMBOL(rxrpc_get_server_data_key);
+
+/**
+ * rxrpc_get_null_key - Generate a null RxRPC key
+ * @keyname: The name to give the key.
+ *
+ * Generate a null RxRPC key that can be used to indicate anonymous security is
+ * required for a particular domain.
+ *
+ * Return: The new key or a negative error code.
+ */
+struct key *rxrpc_get_null_key(const char *keyname)
+{
+	const struct cred *cred = current_cred();
+	struct key *key;
+	int ret;
+
+	key = key_alloc(&key_type_rxrpc, keyname,
+			GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred,
+			KEY_POS_SEARCH, KEY_ALLOC_NOT_IN_QUOTA, NULL);
+	if (IS_ERR(key))
+		return key;
+
+	ret = key_instantiate_and_link(key, NULL, 0, NULL, NULL);
+	if (ret < 0) {
+		key_revoke(key);
+		key_put(key);
+		return ERR_PTR(ret);
+	}
+
+	return key;
+}
+EXPORT_SYMBOL(rxrpc_get_null_key);
+
+/*
+ * read the contents of an rxrpc key
+ * - this returns the result in XDR form
+ */
+static long rxrpc_read(const struct key *key,
+		       char *buffer, size_t buflen)
+{
+	const struct rxrpc_key_token *token;
+	size_t size;
+	__be32 *xdr, *oldxdr;
+	u32 cnlen, toksize, ntoks, tok, zero;
+	u16 toksizes[AFSTOKEN_MAX];
+
+	_enter("");
+
+	/* we don't know what form we should return non-AFS keys in */
+	if (memcmp(key->description, "afs@", 4) != 0)
+		return -EOPNOTSUPP;
+	cnlen = strlen(key->description + 4);
+
+#define RND(X) (((X) + 3) & ~3)
+
+	/* AFS keys we return in XDR form, so we need to work out the size of
+	 * the XDR */
+	size = 2 * 4;	/* flags, cellname len */
+	size += RND(cnlen);	/* cellname */
+	size += 1 * 4;	/* token count */
+
+	ntoks = 0;
+	for (token = key->payload.data[0]; token; token = token->next) {
+		toksize = 4;	/* sec index */
+
+		switch (token->security_index) {
+		case RXRPC_SECURITY_RXKAD:
+			toksize += 8 * 4;	/* viceid, kvno, key*2, begin,
+						 * end, primary, tktlen */
+			if (!token->no_leak_key)
+				toksize += RND(token->kad->ticket_len);
+			break;
+
+		case RXRPC_SECURITY_YFS_RXGK:
+			toksize += 6 * 8 + 2 * 4;
+			if (!token->no_leak_key)
+				toksize += RND(token->rxgk->key.len);
+			toksize += RND(token->rxgk->ticket.len);
+			break;
+
+		default: /* we have a ticket we can't encode */
+			pr_err("Unsupported key token type (%u)\n",
+			       token->security_index);
+			return -ENOPKG;
+		}
+
+		_debug("token[%u]: toksize=%u", ntoks, toksize);
+		if (WARN_ON(toksize > AFSTOKEN_LENGTH_MAX))
+			return -EIO;
+
+		toksizes[ntoks++] = toksize;
+		size += toksize + 4; /* each token has a length word */
+	}
+
+#undef RND
+
+	if (!buffer || buflen < size)
+		return size;
+
+	xdr = (__be32 *)buffer;
+	zero = 0;
+#define ENCODE(x)				\
+	do {					\
+		*xdr++ = htonl(x);		\
+	} while(0)
+#define ENCODE_DATA(l, s)						\
+	do {								\
+		u32 _l = (l);						\
+		ENCODE(l);						\
+		memcpy(xdr, (s), _l);					\
+		if (_l & 3)						\
+			memcpy((u8 *)xdr + _l, &zero, 4 - (_l & 3));	\
+		xdr += (_l + 3) >> 2;					\
+	} while(0)
+#define ENCODE_BYTES(l, s)						\
+	do {								\
+		u32 _l = (l);						\
+		memcpy(xdr, (s), _l);					\
+		if (_l & 3)						\
+			memcpy((u8 *)xdr + _l, &zero, 4 - (_l & 3));	\
+		xdr += (_l + 3) >> 2;					\
+	} while(0)
+#define ENCODE64(x)					\
+	do {						\
+		__be64 y = cpu_to_be64(x);		\
+		memcpy(xdr, &y, 8);			\
+		xdr += 8 >> 2;				\
+	} while(0)
+#define ENCODE_STR(s)				\
+	do {					\
+		const char *_s = (s);		\
+		ENCODE_DATA(strlen(_s), _s);	\
+	} while(0)
+
+	ENCODE(0);					/* flags */
+	ENCODE_DATA(cnlen, key->description + 4);	/* cellname */
+	ENCODE(ntoks);
+
+	tok = 0;
+	for (token = key->payload.data[0]; token; token = token->next) {
+		toksize = toksizes[tok++];
+		ENCODE(toksize);
+		oldxdr = xdr;
+		ENCODE(token->security_index);
+
+		switch (token->security_index) {
+		case RXRPC_SECURITY_RXKAD:
+			ENCODE(token->kad->vice_id);
+			ENCODE(token->kad->kvno);
+			ENCODE_BYTES(8, token->kad->session_key);
+			ENCODE(token->kad->start);
+			ENCODE(token->kad->expiry);
+			ENCODE(token->kad->primary_flag);
+			if (token->no_leak_key)
+				ENCODE(0);
+			else
+				ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
+			break;
+
+		case RXRPC_SECURITY_YFS_RXGK:
+			ENCODE64(token->rxgk->begintime);
+			ENCODE64(token->rxgk->endtime);
+			ENCODE64(token->rxgk->level);
+			ENCODE64(token->rxgk->lifetime);
+			ENCODE64(token->rxgk->bytelife);
+			ENCODE64(token->rxgk->enctype);
+			if (token->no_leak_key)
+				ENCODE(0);
+			else
+				ENCODE_DATA(token->rxgk->key.len, token->rxgk->key.data);
+			ENCODE_DATA(token->rxgk->ticket.len, token->rxgk->ticket.data);
+			break;
+
+		default:
+			pr_err("Unsupported key token type (%u)\n",
+			       token->security_index);
+			return -ENOPKG;
+		}
+
+		if (WARN_ON((unsigned long)xdr - (unsigned long)oldxdr !=
+			    toksize))
+			return -EIO;
+	}
+
+#undef ENCODE_STR
+#undef ENCODE_DATA
+#undef ENCODE64
+#undef ENCODE
+
+	if (WARN_ON(tok != ntoks))
+		return -EIO;
+	if (WARN_ON((unsigned long)xdr - (unsigned long)buffer != size))
+		return -EIO;
+	_leave(" = %zu", size);
+	return size;
+}