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, 581 insertions, 0 deletions

diff --git a/fs/lockd/mon.c b/fs/lockd/mon.c
new file mode 100644
index 000000000..a8f5ac6f0
--- /dev/null
+++ b/fs/lockd/mon.c
@@ -0,0 +1,581 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/lockd/mon.c
+ *
+ * The kernel statd client.
+ *
+ * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/ktime.h>
+#include <linux/slab.h>
+
+#include <linux/sunrpc/clnt.h>
+#include <linux/sunrpc/addr.h>
+#include <linux/sunrpc/xprtsock.h>
+#include <linux/sunrpc/svc.h>
+
+#include <linux/unaligned.h>
+
+#include "lockd.h"
+#include "netns.h"
+
+#define NLMDBG_FACILITY		NLMDBG_MONITOR
+#define NSM_PROGRAM		100024
+#define NSM_VERSION		1
+
+enum {
+	NSMPROC_NULL,
+	NSMPROC_STAT,
+	NSMPROC_MON,
+	NSMPROC_UNMON,
+	NSMPROC_UNMON_ALL,
+	NSMPROC_SIMU_CRASH,
+	NSMPROC_NOTIFY,
+};
+
+struct nsm_args {
+	struct nsm_private	*priv;
+	u32			prog;		/* RPC callback info */
+	u32			vers;
+	u32			proc;
+
+	char			*mon_name;
+	const char		*nodename;
+};
+
+struct nsm_res {
+	u32			status;
+	u32			state;
+};
+
+static const struct rpc_program	nsm_program;
+static				DEFINE_SPINLOCK(nsm_lock);
+
+/*
+ * Local NSM state
+ */
+u32	__read_mostly		nsm_local_state;
+bool	__read_mostly		nsm_use_hostnames;
+
+static inline struct sockaddr *nsm_addr(const struct nsm_handle *nsm)
+{
+	return (struct sockaddr *)&nsm->sm_addr;
+}
+
+static struct rpc_clnt *nsm_create(struct net *net, const char *nodename)
+{
+	struct sockaddr_in sin = {
+		.sin_family		= AF_INET,
+		.sin_addr.s_addr	= htonl(INADDR_LOOPBACK),
+	};
+	struct rpc_create_args args = {
+		.net			= net,
+		.protocol		= XPRT_TRANSPORT_TCP,
+		.address		= (struct sockaddr *)&sin,
+		.addrsize		= sizeof(sin),
+		.servername		= "rpc.statd",
+		.nodename		= nodename,
+		.program		= &nsm_program,
+		.version		= NSM_VERSION,
+		.authflavor		= RPC_AUTH_NULL,
+		.flags			= RPC_CLNT_CREATE_NOPING,
+		.cred			= current_cred(),
+	};
+
+	return rpc_create(&args);
+}
+
+static int nsm_mon_unmon(struct nsm_handle *nsm, u32 proc, struct nsm_res *res,
+			 const struct nlm_host *host)
+{
+	int		status;
+	struct rpc_clnt *clnt;
+	struct nsm_args args = {
+		.priv		= &nsm->sm_priv,
+		.prog		= NLM_PROGRAM,
+		.vers		= 3,
+		.proc		= NLMPROC_NSM_NOTIFY,
+		.mon_name	= nsm->sm_mon_name,
+		.nodename	= host->nodename,
+	};
+	struct rpc_message msg = {
+		.rpc_argp	= &args,
+		.rpc_resp	= res,
+	};
+
+	memset(res, 0, sizeof(*res));
+
+	clnt = nsm_create(host->net, host->nodename);
+	if (IS_ERR(clnt)) {
+		dprintk("lockd: failed to create NSM upcall transport, "
+			"status=%ld, net=%x\n", PTR_ERR(clnt),
+			host->net->ns.inum);
+		return PTR_ERR(clnt);
+	}
+
+	msg.rpc_proc = &clnt->cl_procinfo[proc];
+	status = rpc_call_sync(clnt, &msg, RPC_TASK_SOFTCONN);
+	if (status == -ECONNREFUSED) {
+		dprintk("lockd:	NSM upcall RPC failed, status=%d, forcing rebind\n",
+				status);
+		rpc_force_rebind(clnt);
+		status = rpc_call_sync(clnt, &msg, RPC_TASK_SOFTCONN);
+	}
+	if (status < 0)
+		dprintk("lockd: NSM upcall RPC failed, status=%d\n",
+				status);
+	else
+		status = 0;
+
+	rpc_shutdown_client(clnt);
+	return status;
+}
+
+/**
+ * nsm_monitor - Notify a peer in case we reboot
+ * @host: pointer to nlm_host of peer to notify
+ *
+ * If this peer is not already monitored, this function sends an
+ * upcall to the local rpc.statd to record the name/address of
+ * the peer to notify in case we reboot.
+ *
+ * Returns zero if the peer is monitored by the local rpc.statd;
+ * otherwise a negative errno value is returned.
+ */
+int nsm_monitor(const struct nlm_host *host)
+{
+	struct nsm_handle *nsm = host->h_nsmhandle;
+	struct nsm_res	res;
+	int		status;
+
+	dprintk("lockd: nsm_monitor(%s)\n", nsm->sm_name);
+
+	if (nsm->sm_monitored)
+		return 0;
+
+	/*
+	 * Choose whether to record the caller_name or IP address of
+	 * this peer in the local rpc.statd's database.
+	 */
+	nsm->sm_mon_name = nsm_use_hostnames ? nsm->sm_name : nsm->sm_addrbuf;
+
+	status = nsm_mon_unmon(nsm, NSMPROC_MON, &res, host);
+	if (unlikely(res.status != 0))
+		status = -EIO;
+	if (unlikely(status < 0)) {
+		pr_notice_ratelimited("lockd: cannot monitor %s\n", nsm->sm_name);
+		return status;
+	}
+
+	nsm->sm_monitored = 1;
+	if (unlikely(nsm_local_state != res.state)) {
+		nsm_local_state = res.state;
+		dprintk("lockd: NSM state changed to %d\n", nsm_local_state);
+	}
+	return 0;
+}
+
+/**
+ * nsm_unmonitor - Unregister peer notification
+ * @host: pointer to nlm_host of peer to stop monitoring
+ *
+ * If this peer is monitored, this function sends an upcall to
+ * tell the local rpc.statd not to send this peer a notification
+ * when we reboot.
+ */
+void nsm_unmonitor(const struct nlm_host *host)
+{
+	struct nsm_handle *nsm = host->h_nsmhandle;
+	struct nsm_res	res;
+	int status;
+
+	if (refcount_read(&nsm->sm_count) == 1
+	 && nsm->sm_monitored && !nsm->sm_sticky) {
+		dprintk("lockd: nsm_unmonitor(%s)\n", nsm->sm_name);
+
+		status = nsm_mon_unmon(nsm, NSMPROC_UNMON, &res, host);
+		if (res.status != 0)
+			status = -EIO;
+		if (status < 0)
+			printk(KERN_NOTICE "lockd: cannot unmonitor %s\n",
+					nsm->sm_name);
+		else
+			nsm->sm_monitored = 0;
+	}
+}
+
+static struct nsm_handle *nsm_lookup_hostname(const struct list_head *nsm_handles,
+					const char *hostname, const size_t len)
+{
+	struct nsm_handle *nsm;
+
+	list_for_each_entry(nsm, nsm_handles, sm_link)
+		if (strlen(nsm->sm_name) == len &&
+		    memcmp(nsm->sm_name, hostname, len) == 0)
+			return nsm;
+	return NULL;
+}
+
+static struct nsm_handle *nsm_lookup_addr(const struct list_head *nsm_handles,
+					const struct sockaddr *sap)
+{
+	struct nsm_handle *nsm;
+
+	list_for_each_entry(nsm, nsm_handles, sm_link)
+		if (rpc_cmp_addr(nsm_addr(nsm), sap))
+			return nsm;
+	return NULL;
+}
+
+static struct nsm_handle *nsm_lookup_priv(const struct list_head *nsm_handles,
+					const struct nsm_private *priv)
+{
+	struct nsm_handle *nsm;
+
+	list_for_each_entry(nsm, nsm_handles, sm_link)
+		if (memcmp(nsm->sm_priv.data, priv->data,
+					sizeof(priv->data)) == 0)
+			return nsm;
+	return NULL;
+}
+
+/*
+ * Construct a unique cookie to match this nsm_handle to this monitored
+ * host.  It is passed to the local rpc.statd via NSMPROC_MON, and
+ * returned via NLMPROC_SM_NOTIFY, in the "priv" field of these
+ * requests.
+ *
+ * The NSM protocol requires that these cookies be unique while the
+ * system is running.  We prefer a stronger requirement of making them
+ * unique across reboots.  If user space bugs cause a stale cookie to
+ * be sent to the kernel, it could cause the wrong host to lose its
+ * lock state if cookies were not unique across reboots.
+ *
+ * The cookies are exposed only to local user space via loopback.  They
+ * do not appear on the physical network.  If we want greater security
+ * for some reason, nsm_init_private() could perform a one-way hash to
+ * obscure the contents of the cookie.
+ */
+static void nsm_init_private(struct nsm_handle *nsm)
+{
+	u64 *p = (u64 *)&nsm->sm_priv.data;
+	s64 ns;
+
+	ns = ktime_get_ns();
+	put_unaligned(ns, p);
+	put_unaligned((unsigned long)nsm, p + 1);
+}
+
+static struct nsm_handle *nsm_create_handle(const struct sockaddr *sap,
+					    const size_t salen,
+					    const char *hostname,
+					    const size_t hostname_len)
+{
+	struct nsm_handle *new;
+
+	if (!hostname)
+		return NULL;
+
+	new = kzalloc(sizeof(*new) + hostname_len + 1, GFP_KERNEL);
+	if (unlikely(new == NULL))
+		return NULL;
+
+	refcount_set(&new->sm_count, 1);
+	new->sm_name = (char *)(new + 1);
+	memcpy(nsm_addr(new), sap, salen);
+	new->sm_addrlen = salen;
+	nsm_init_private(new);
+
+	if (rpc_ntop(nsm_addr(new), new->sm_addrbuf,
+					sizeof(new->sm_addrbuf)) == 0)
+		(void)snprintf(new->sm_addrbuf, sizeof(new->sm_addrbuf),
+				"unsupported address family");
+	memcpy(new->sm_name, hostname, hostname_len);
+	new->sm_name[hostname_len] = '\0';
+
+	return new;
+}
+
+/**
+ * nsm_get_handle - Find or create a cached nsm_handle
+ * @net: network namespace
+ * @sap: pointer to socket address of handle to find
+ * @salen: length of socket address
+ * @hostname: pointer to C string containing hostname to find
+ * @hostname_len: length of C string
+ *
+ * Behavior is modulated by the global nsm_use_hostnames variable.
+ *
+ * Returns a cached nsm_handle after bumping its ref count, or
+ * returns a fresh nsm_handle if a handle that matches @sap and/or
+ * @hostname cannot be found in the handle cache.  Returns NULL if
+ * an error occurs.
+ */
+struct nsm_handle *nsm_get_handle(const struct net *net,
+				  const struct sockaddr *sap,
+				  const size_t salen, const char *hostname,
+				  const size_t hostname_len)
+{
+	struct nsm_handle *cached, *new = NULL;
+	struct lockd_net *ln = net_generic(net, lockd_net_id);
+
+	if (hostname && memchr(hostname, '/', hostname_len) != NULL) {
+		if (printk_ratelimit()) {
+			printk(KERN_WARNING "Invalid hostname \"%.*s\" "
+					    "in NFS lock request\n",
+				(int)hostname_len, hostname);
+		}
+		return NULL;
+	}
+
+retry:
+	spin_lock(&nsm_lock);
+
+	if (nsm_use_hostnames && hostname != NULL)
+		cached = nsm_lookup_hostname(&ln->nsm_handles,
+					hostname, hostname_len);
+	else
+		cached = nsm_lookup_addr(&ln->nsm_handles, sap);
+
+	if (cached != NULL) {
+		refcount_inc(&cached->sm_count);
+		spin_unlock(&nsm_lock);
+		kfree(new);
+		dprintk("lockd: found nsm_handle for %s (%s), "
+				"cnt %d\n", cached->sm_name,
+				cached->sm_addrbuf,
+				refcount_read(&cached->sm_count));
+		return cached;
+	}
+
+	if (new != NULL) {
+		list_add(&new->sm_link, &ln->nsm_handles);
+		spin_unlock(&nsm_lock);
+		dprintk("lockd: created nsm_handle for %s (%s)\n",
+				new->sm_name, new->sm_addrbuf);
+		return new;
+	}
+
+	spin_unlock(&nsm_lock);
+
+	new = nsm_create_handle(sap, salen, hostname, hostname_len);
+	if (unlikely(new == NULL))
+		return NULL;
+	goto retry;
+}
+
+/**
+ * nsm_reboot_lookup - match NLMPROC_SM_NOTIFY arguments to an nsm_handle
+ * @net:  network namespace
+ * @info: pointer to NLMPROC_SM_NOTIFY arguments
+ *
+ * Returns a matching nsm_handle if found in the nsm cache. The returned
+ * nsm_handle's reference count is bumped. Otherwise returns NULL if some
+ * error occurred.
+ */
+struct nsm_handle *nsm_reboot_lookup(const struct net *net,
+				const struct lockd_reboot *info)
+{
+	struct nsm_handle *cached;
+	struct lockd_net *ln = net_generic(net, lockd_net_id);
+
+	spin_lock(&nsm_lock);
+
+	cached = nsm_lookup_priv(&ln->nsm_handles, &info->priv);
+	if (unlikely(cached == NULL)) {
+		spin_unlock(&nsm_lock);
+		dprintk("lockd: never saw rebooted peer '%.*s' before\n",
+				info->len, info->mon);
+		return cached;
+	}
+
+	refcount_inc(&cached->sm_count);
+	spin_unlock(&nsm_lock);
+
+	dprintk("lockd: host %s (%s) rebooted, cnt %d\n",
+			cached->sm_name, cached->sm_addrbuf,
+			refcount_read(&cached->sm_count));
+	return cached;
+}
+
+/**
+ * nsm_release - Release an NSM handle
+ * @nsm: pointer to handle to be released
+ *
+ */
+void nsm_release(struct nsm_handle *nsm)
+{
+	if (refcount_dec_and_lock(&nsm->sm_count, &nsm_lock)) {
+		list_del(&nsm->sm_link);
+		spin_unlock(&nsm_lock);
+		dprintk("lockd: destroyed nsm_handle for %s (%s)\n",
+				nsm->sm_name, nsm->sm_addrbuf);
+		kfree(nsm);
+	}
+}
+
+/*
+ * XDR functions for NSM.
+ *
+ * See https://www.opengroup.org/ for details on the Network
+ * Status Monitor wire protocol.
+ */
+
+static void encode_nsm_string(struct xdr_stream *xdr, const char *string)
+{
+	const u32 len = strlen(string);
+	__be32 *p;
+
+	p = xdr_reserve_space(xdr, 4 + len);
+	xdr_encode_opaque(p, string, len);
+}
+
+/*
+ * "mon_name" specifies the host to be monitored.
+ */
+static void encode_mon_name(struct xdr_stream *xdr, const struct nsm_args *argp)
+{
+	encode_nsm_string(xdr, argp->mon_name);
+}
+
+/*
+ * The "my_id" argument specifies the hostname and RPC procedure
+ * to be called when the status manager receives notification
+ * (via the NLMPROC_SM_NOTIFY call) that the state of host "mon_name"
+ * has changed.
+ */
+static void encode_my_id(struct xdr_stream *xdr, const struct nsm_args *argp)
+{
+	__be32 *p;
+
+	encode_nsm_string(xdr, argp->nodename);
+	p = xdr_reserve_space(xdr, 4 + 4 + 4);
+	*p++ = cpu_to_be32(argp->prog);
+	*p++ = cpu_to_be32(argp->vers);
+	*p = cpu_to_be32(argp->proc);
+}
+
+/*
+ * The "mon_id" argument specifies the non-private arguments
+ * of an NSMPROC_MON or NSMPROC_UNMON call.
+ */
+static void encode_mon_id(struct xdr_stream *xdr, const struct nsm_args *argp)
+{
+	encode_mon_name(xdr, argp);
+	encode_my_id(xdr, argp);
+}
+
+/*
+ * The "priv" argument may contain private information required
+ * by the NSMPROC_MON call. This information will be supplied in the
+ * NLMPROC_SM_NOTIFY call.
+ */
+static void encode_priv(struct xdr_stream *xdr, const struct nsm_args *argp)
+{
+	__be32 *p;
+
+	p = xdr_reserve_space(xdr, SM_PRIV_SIZE);
+	xdr_encode_opaque_fixed(p, argp->priv->data, SM_PRIV_SIZE);
+}
+
+static void nsm_xdr_enc_mon(struct rpc_rqst *req, struct xdr_stream *xdr,
+			    const void *argp)
+{
+	encode_mon_id(xdr, argp);
+	encode_priv(xdr, argp);
+}
+
+static void nsm_xdr_enc_unmon(struct rpc_rqst *req, struct xdr_stream *xdr,
+			      const void *argp)
+{
+	encode_mon_id(xdr, argp);
+}
+
+static int nsm_xdr_dec_stat_res(struct rpc_rqst *rqstp,
+				struct xdr_stream *xdr,
+				void *data)
+{
+	struct nsm_res *resp = data;
+	__be32 *p;
+
+	p = xdr_inline_decode(xdr, 4 + 4);
+	if (unlikely(p == NULL))
+		return -EIO;
+	resp->status = be32_to_cpup(p++);
+	resp->state = be32_to_cpup(p);
+
+	dprintk("lockd: %s status %d state %d\n",
+		__func__, resp->status, resp->state);
+	return 0;
+}
+
+static int nsm_xdr_dec_stat(struct rpc_rqst *rqstp,
+			    struct xdr_stream *xdr,
+			    void *data)
+{
+	struct nsm_res *resp = data;
+	__be32 *p;
+
+	p = xdr_inline_decode(xdr, 4);
+	if (unlikely(p == NULL))
+		return -EIO;
+	resp->state = be32_to_cpup(p);
+
+	dprintk("lockd: %s state %d\n", __func__, resp->state);
+	return 0;
+}
+
+#define SM_my_name_sz	(1+XDR_QUADLEN(SM_MAXSTRLEN))
+#define SM_my_id_sz	(SM_my_name_sz+3)
+#define SM_mon_name_sz	(1+XDR_QUADLEN(SM_MAXSTRLEN))
+#define SM_mon_id_sz	(SM_mon_name_sz+SM_my_id_sz)
+#define SM_priv_sz	(XDR_QUADLEN(SM_PRIV_SIZE))
+#define SM_mon_sz	(SM_mon_id_sz+SM_priv_sz)
+#define SM_monres_sz	2
+#define SM_unmonres_sz	1
+
+static const struct rpc_procinfo nsm_procedures[] = {
+[NSMPROC_MON] = {
+		.p_proc		= NSMPROC_MON,
+		.p_encode	= nsm_xdr_enc_mon,
+		.p_decode	= nsm_xdr_dec_stat_res,
+		.p_arglen	= SM_mon_sz,
+		.p_replen	= SM_monres_sz,
+		.p_statidx	= NSMPROC_MON,
+		.p_name		= "MONITOR",
+	},
+[NSMPROC_UNMON] = {
+		.p_proc		= NSMPROC_UNMON,
+		.p_encode	= nsm_xdr_enc_unmon,
+		.p_decode	= nsm_xdr_dec_stat,
+		.p_arglen	= SM_mon_id_sz,
+		.p_replen	= SM_unmonres_sz,
+		.p_statidx	= NSMPROC_UNMON,
+		.p_name		= "UNMONITOR",
+	},
+};
+
+static unsigned int nsm_version1_counts[ARRAY_SIZE(nsm_procedures)];
+static const struct rpc_version nsm_version1 = {
+	.number		= 1,
+	.nrprocs	= ARRAY_SIZE(nsm_procedures),
+	.procs		= nsm_procedures,
+	.counts		= nsm_version1_counts,
+};
+
+static const struct rpc_version *nsm_version[] = {
+	[1] = &nsm_version1,
+};
+
+static struct rpc_stat		nsm_stats;
+
+static const struct rpc_program nsm_program = {
+	.name		= "statd",
+	.number		= NSM_PROGRAM,
+	.nrvers		= ARRAY_SIZE(nsm_version),
+	.version	= nsm_version,
+	.stats		= &nsm_stats
+};