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, 496 insertions, 0 deletions

diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c
new file mode 100644
index 000000000..47824120f
--- /dev/null
+++ b/net/rxrpc/call_accept.c
@@ -0,0 +1,496 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* incoming call handling
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/net.h>
+#include <linux/skbuff.h>
+#include <linux/errqueue.h>
+#include <linux/udp.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <linux/icmp.h>
+#include <linux/gfp.h>
+#include <linux/circ_buf.h>
+#include <net/sock.h>
+#include <net/af_rxrpc.h>
+#include <net/ip.h>
+#include "ar-internal.h"
+
+static void rxrpc_dummy_notify(struct sock *sk, struct rxrpc_call *call,
+			       unsigned long user_call_ID)
+{
+}
+
+/*
+ * Preallocate a single service call, connection and peer and, if possible,
+ * give them a user ID and attach the user's side of the ID to them.
+ */
+static int rxrpc_service_prealloc_one(struct rxrpc_sock *rx,
+				      struct rxrpc_backlog *b,
+				      rxrpc_notify_rx_t notify_rx,
+				      unsigned long user_call_ID, gfp_t gfp,
+				      unsigned int debug_id)
+{
+	struct rxrpc_call *call, *xcall;
+	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
+	struct rb_node *parent, **pp;
+	int max, tmp;
+	unsigned int size = RXRPC_BACKLOG_MAX;
+	unsigned int head, tail, call_head, call_tail;
+
+	max = rx->sk.sk_max_ack_backlog;
+	tmp = rx->sk.sk_ack_backlog;
+	if (tmp >= max) {
+		_leave(" = -ENOBUFS [full %u]", max);
+		return -ENOBUFS;
+	}
+	max -= tmp;
+
+	/* We don't need more conns and peers than we have calls, but on the
+	 * other hand, we shouldn't ever use more peers than conns or conns
+	 * than calls.
+	 */
+	call_head = b->call_backlog_head;
+	call_tail = READ_ONCE(b->call_backlog_tail);
+	tmp = CIRC_CNT(call_head, call_tail, size);
+	if (tmp >= max) {
+		_leave(" = -ENOBUFS [enough %u]", tmp);
+		return -ENOBUFS;
+	}
+	max = tmp + 1;
+
+	head = b->peer_backlog_head;
+	tail = READ_ONCE(b->peer_backlog_tail);
+	if (CIRC_CNT(head, tail, size) < max) {
+		struct rxrpc_peer *peer;
+
+		peer = rxrpc_alloc_peer(rx->local, gfp, rxrpc_peer_new_prealloc);
+		if (!peer)
+			return -ENOMEM;
+		b->peer_backlog[head] = peer;
+		smp_store_release(&b->peer_backlog_head,
+				  (head + 1) & (size - 1));
+	}
+
+	head = b->conn_backlog_head;
+	tail = READ_ONCE(b->conn_backlog_tail);
+	if (CIRC_CNT(head, tail, size) < max) {
+		struct rxrpc_connection *conn;
+
+		conn = rxrpc_prealloc_service_connection(rxnet, gfp);
+		if (!conn)
+			return -ENOMEM;
+		b->conn_backlog[head] = conn;
+		smp_store_release(&b->conn_backlog_head,
+				  (head + 1) & (size - 1));
+	}
+
+	/* Now it gets complicated, because calls get registered with the
+	 * socket here, with a user ID preassigned by the user.
+	 */
+	call = rxrpc_alloc_call(rx, gfp, debug_id);
+	if (!call)
+		return -ENOMEM;
+	call->flags |= (1 << RXRPC_CALL_IS_SERVICE);
+	rxrpc_set_call_state(call, RXRPC_CALL_SERVER_PREALLOC);
+	__set_bit(RXRPC_CALL_EV_INITIAL_PING, &call->events);
+
+	trace_rxrpc_call(call->debug_id, refcount_read(&call->ref),
+			 user_call_ID, rxrpc_call_new_prealloc_service);
+
+	write_lock(&rx->call_lock);
+
+	/* Check the user ID isn't already in use */
+	pp = &rx->calls.rb_node;
+	parent = NULL;
+	while (*pp) {
+		parent = *pp;
+		xcall = rb_entry(parent, struct rxrpc_call, sock_node);
+		if (user_call_ID < xcall->user_call_ID)
+			pp = &(*pp)->rb_left;
+		else if (user_call_ID > xcall->user_call_ID)
+			pp = &(*pp)->rb_right;
+		else
+			goto id_in_use;
+	}
+
+	call->user_call_ID = user_call_ID;
+	call->notify_rx = notify_rx;
+	if (rx->app_ops &&
+	    rx->app_ops->user_attach_call) {
+		rxrpc_get_call(call, rxrpc_call_get_kernel_service);
+		rx->app_ops->user_attach_call(call, user_call_ID);
+	}
+
+	rxrpc_get_call(call, rxrpc_call_get_userid);
+	rb_link_node(&call->sock_node, parent, pp);
+	rb_insert_color(&call->sock_node, &rx->calls);
+	set_bit(RXRPC_CALL_HAS_USERID, &call->flags);
+
+	list_add(&call->sock_link, &rx->sock_calls);
+
+	write_unlock(&rx->call_lock);
+
+	rxnet = call->rxnet;
+	spin_lock(&rxnet->call_lock);
+	list_add_tail_rcu(&call->link, &rxnet->calls);
+	spin_unlock(&rxnet->call_lock);
+
+	b->call_backlog[call_head] = call;
+	smp_store_release(&b->call_backlog_head, (call_head + 1) & (size - 1));
+	_leave(" = 0 [%d -> %lx]", call->debug_id, user_call_ID);
+	return 0;
+
+id_in_use:
+	write_unlock(&rx->call_lock);
+	rxrpc_prefail_call(call, RXRPC_CALL_LOCAL_ERROR, -EBADSLT);
+	rxrpc_cleanup_call(call);
+	_leave(" = -EBADSLT");
+	return -EBADSLT;
+}
+
+/*
+ * Allocate the preallocation buffers for incoming service calls.  These must
+ * be charged manually.
+ */
+int rxrpc_service_prealloc(struct rxrpc_sock *rx, gfp_t gfp)
+{
+	struct rxrpc_backlog *b = rx->backlog;
+
+	if (!b) {
+		b = kzalloc_obj(struct rxrpc_backlog, gfp);
+		if (!b)
+			return -ENOMEM;
+		rx->backlog = b;
+	}
+
+	return 0;
+}
+
+/*
+ * Discard the preallocation on a service.
+ */
+void rxrpc_discard_prealloc(struct rxrpc_sock *rx)
+{
+	struct rxrpc_backlog *b = rx->backlog;
+	struct rxrpc_net *rxnet = rxrpc_net(sock_net(&rx->sk));
+	unsigned int size = RXRPC_BACKLOG_MAX, head, tail;
+
+	if (!b)
+		return;
+	rx->backlog = NULL;
+
+	/* Make sure that there aren't any incoming calls in progress before we
+	 * clear the preallocation buffers.
+	 */
+	spin_lock_irq(&rx->incoming_lock);
+	spin_unlock_irq(&rx->incoming_lock);
+
+	head = b->peer_backlog_head;
+	tail = b->peer_backlog_tail;
+	while (CIRC_CNT(head, tail, size) > 0) {
+		struct rxrpc_peer *peer = b->peer_backlog[tail];
+		rxrpc_put_local(peer->local, rxrpc_local_put_prealloc_peer);
+		kfree(peer);
+		tail = (tail + 1) & (size - 1);
+	}
+
+	head = b->conn_backlog_head;
+	tail = b->conn_backlog_tail;
+	while (CIRC_CNT(head, tail, size) > 0) {
+		struct rxrpc_connection *conn = b->conn_backlog[tail];
+		write_lock(&rxnet->conn_lock);
+		list_del(&conn->link);
+		list_del(&conn->proc_link);
+		write_unlock(&rxnet->conn_lock);
+		kfree(conn);
+		if (atomic_dec_and_test(&rxnet->nr_conns))
+			wake_up_var(&rxnet->nr_conns);
+		tail = (tail + 1) & (size - 1);
+	}
+
+	head = b->call_backlog_head;
+	tail = b->call_backlog_tail;
+	while (CIRC_CNT(head, tail, size) > 0) {
+		struct rxrpc_call *call = b->call_backlog[tail];
+		rxrpc_see_call(call, rxrpc_call_see_discard);
+		rcu_assign_pointer(call->socket, rx);
+		if (rx->app_ops &&
+		    rx->app_ops->discard_new_call) {
+			_debug("discard %lx", call->user_call_ID);
+			rx->app_ops->discard_new_call(call, call->user_call_ID);
+			if (call->notify_rx)
+				call->notify_rx = rxrpc_dummy_notify;
+			rxrpc_put_call(call, rxrpc_call_put_kernel);
+		}
+		rxrpc_call_completed(call);
+		rxrpc_release_call(rx, call);
+		rxrpc_put_call(call, rxrpc_call_put_discard_prealloc);
+		tail = (tail + 1) & (size - 1);
+	}
+
+	kfree(b);
+}
+
+/*
+ * Allocate a new incoming call from the prealloc pool, along with a connection
+ * and a peer as necessary.
+ */
+static struct rxrpc_call *rxrpc_alloc_incoming_call(struct rxrpc_sock *rx,
+						    struct rxrpc_local *local,
+						    struct rxrpc_peer *peer,
+						    struct rxrpc_connection *conn,
+						    const struct rxrpc_security *sec,
+						    struct sockaddr_rxrpc *peer_srx,
+						    struct sk_buff *skb)
+{
+	struct rxrpc_backlog *b = rx->backlog;
+	struct rxrpc_call *call;
+	unsigned short call_head, conn_head, peer_head;
+	unsigned short call_tail, conn_tail, peer_tail;
+	unsigned short call_count, conn_count;
+
+	if (!b)
+		return NULL;
+
+	/* #calls >= #conns >= #peers must hold true. */
+	call_head = smp_load_acquire(&b->call_backlog_head);
+	call_tail = b->call_backlog_tail;
+	call_count = CIRC_CNT(call_head, call_tail, RXRPC_BACKLOG_MAX);
+	conn_head = smp_load_acquire(&b->conn_backlog_head);
+	conn_tail = b->conn_backlog_tail;
+	conn_count = CIRC_CNT(conn_head, conn_tail, RXRPC_BACKLOG_MAX);
+	ASSERTCMP(conn_count, >=, call_count);
+	peer_head = smp_load_acquire(&b->peer_backlog_head);
+	peer_tail = b->peer_backlog_tail;
+	ASSERTCMP(CIRC_CNT(peer_head, peer_tail, RXRPC_BACKLOG_MAX), >=,
+		  conn_count);
+
+	if (call_count == 0)
+		return NULL;
+
+	if (!conn) {
+		if (peer && !rxrpc_get_peer_maybe(peer, rxrpc_peer_get_service_conn))
+			peer = NULL;
+		if (!peer) {
+			peer = b->peer_backlog[peer_tail];
+			peer->srx = *peer_srx;
+			b->peer_backlog[peer_tail] = NULL;
+			smp_store_release(&b->peer_backlog_tail,
+					  (peer_tail + 1) &
+					  (RXRPC_BACKLOG_MAX - 1));
+
+			rxrpc_new_incoming_peer(local, peer);
+		}
+
+		/* Now allocate and set up the connection */
+		conn = b->conn_backlog[conn_tail];
+		b->conn_backlog[conn_tail] = NULL;
+		smp_store_release(&b->conn_backlog_tail,
+				  (conn_tail + 1) & (RXRPC_BACKLOG_MAX - 1));
+		conn->local = rxrpc_get_local(local, rxrpc_local_get_prealloc_conn);
+		conn->peer = peer;
+		rxrpc_see_connection(conn, rxrpc_conn_see_new_service_conn);
+		rxrpc_new_incoming_connection(rx, conn, sec, skb);
+	} else {
+		rxrpc_get_connection(conn, rxrpc_conn_get_service_conn);
+		atomic_inc(&conn->active);
+	}
+
+	/* And now we can allocate and set up a new call */
+	call = b->call_backlog[call_tail];
+	b->call_backlog[call_tail] = NULL;
+	smp_store_release(&b->call_backlog_tail,
+			  (call_tail + 1) & (RXRPC_BACKLOG_MAX - 1));
+
+	rxrpc_see_call(call, rxrpc_call_see_accept);
+	call->local = rxrpc_get_local(conn->local, rxrpc_local_get_call);
+	call->conn = conn;
+	call->security = conn->security;
+	call->security_ix = conn->security_ix;
+	call->peer = rxrpc_get_peer(conn->peer, rxrpc_peer_get_accept);
+	call->dest_srx = peer->srx;
+	call->cong_ssthresh = call->peer->cong_ssthresh;
+	call->tx_last_sent = ktime_get_real();
+	return call;
+}
+
+/*
+ * Set up a new incoming call.  Called from the I/O thread.
+ *
+ * If this is for a kernel service, when we allocate the call, it will have
+ * three refs on it: (1) the kernel service, (2) the user_call_ID tree, (3) the
+ * retainer ref obtained from the backlog buffer.  Prealloc calls for userspace
+ * services only have the ref from the backlog buffer.
+ *
+ * If we want to report an error, we mark the skb with the packet type and
+ * abort code and return false.
+ */
+bool rxrpc_new_incoming_call(struct rxrpc_local *local,
+			     struct rxrpc_peer *peer,
+			     struct rxrpc_connection *conn,
+			     struct sockaddr_rxrpc *peer_srx,
+			     struct sk_buff *skb)
+{
+	const struct rxrpc_security *sec = NULL;
+	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+	struct rxrpc_call *call = NULL;
+	struct rxrpc_sock *rx;
+
+	_enter("");
+
+	/* Don't set up a call for anything other than a DATA packet. */
+	if (sp->hdr.type != RXRPC_PACKET_TYPE_DATA)
+		return rxrpc_protocol_error(skb, rxrpc_eproto_no_service_call);
+
+	read_lock_irq(&local->services_lock);
+
+	/* Weed out packets to services we're not offering.  Packets that would
+	 * begin a call are explicitly rejected and the rest are just
+	 * discarded.
+	 */
+	rx = local->service;
+	if (!rx || (sp->hdr.serviceId != rx->srx.srx_service &&
+		    sp->hdr.serviceId != rx->second_service)
+	    ) {
+		if (sp->hdr.type == RXRPC_PACKET_TYPE_DATA &&
+		    sp->hdr.seq == 1)
+			goto unsupported_service;
+		goto discard;
+	}
+
+	if (!conn) {
+		sec = rxrpc_get_incoming_security(rx, skb);
+		if (!sec)
+			goto unsupported_security;
+	}
+
+	spin_lock(&rx->incoming_lock);
+	if (rx->sk.sk_state == RXRPC_SERVER_LISTEN_DISABLED ||
+	    rx->sk.sk_state == RXRPC_CLOSE) {
+		rxrpc_direct_conn_abort(skb, rxrpc_abort_shut_down,
+					RX_INVALID_OPERATION, -ESHUTDOWN);
+		goto no_call;
+	}
+
+	call = rxrpc_alloc_incoming_call(rx, local, peer, conn, sec, peer_srx,
+					 skb);
+	if (!call) {
+		skb->mark = RXRPC_SKB_MARK_REJECT_BUSY;
+		goto no_call;
+	}
+
+	trace_rxrpc_receive(call, rxrpc_receive_incoming,
+			    sp->hdr.serial, sp->hdr.seq);
+
+	/* Make the call live. */
+	rxrpc_incoming_call(rx, call, skb);
+	conn = call->conn;
+
+	if (rx->app_ops &&
+	    rx->app_ops->notify_new_call)
+		rx->app_ops->notify_new_call(&rx->sk, call, call->user_call_ID);
+
+	spin_lock(&conn->state_lock);
+	if (conn->state == RXRPC_CONN_SERVICE_UNSECURED) {
+		conn->state = RXRPC_CONN_SERVICE_CHALLENGING;
+		set_bit(RXRPC_CONN_EV_CHALLENGE, &call->conn->events);
+		rxrpc_queue_conn(call->conn, rxrpc_conn_queue_challenge);
+	}
+	spin_unlock(&conn->state_lock);
+
+	spin_unlock(&rx->incoming_lock);
+	read_unlock_irq(&local->services_lock);
+	rxrpc_assess_MTU_size(local, call->peer);
+
+	if (hlist_unhashed(&call->error_link)) {
+		spin_lock_irq(&call->peer->lock);
+		hlist_add_head(&call->error_link, &call->peer->error_targets);
+		spin_unlock_irq(&call->peer->lock);
+	}
+
+	_leave(" = %p{%d}", call, call->debug_id);
+	rxrpc_queue_rx_call_packet(call, skb);
+	rxrpc_put_call(call, rxrpc_call_put_input);
+	return true;
+
+unsupported_service:
+	read_unlock_irq(&local->services_lock);
+	return rxrpc_direct_conn_abort(skb, rxrpc_abort_service_not_offered,
+				       RX_INVALID_OPERATION, -EOPNOTSUPP);
+unsupported_security:
+	read_unlock_irq(&local->services_lock);
+	return rxrpc_direct_conn_abort(skb, rxrpc_abort_service_not_offered,
+				       RX_INVALID_OPERATION, -EKEYREJECTED);
+no_call:
+	spin_unlock(&rx->incoming_lock);
+	read_unlock_irq(&local->services_lock);
+	_leave(" = f [%u]", skb->mark);
+	return false;
+discard:
+	read_unlock_irq(&local->services_lock);
+	return true;
+}
+
+/*
+ * Charge up socket with preallocated calls, attaching user call IDs.
+ */
+int rxrpc_user_charge_accept(struct rxrpc_sock *rx, unsigned long user_call_ID)
+{
+	struct rxrpc_backlog *b = rx->backlog;
+
+	if (rx->sk.sk_state == RXRPC_CLOSE)
+		return -ESHUTDOWN;
+
+	return rxrpc_service_prealloc_one(rx, b, NULL, user_call_ID, GFP_KERNEL,
+					  atomic_inc_return(&rxrpc_debug_id));
+}
+
+/*
+ * rxrpc_kernel_charge_accept - Charge up socket with preallocated calls
+ * @sock: The socket on which to preallocate
+ * @notify_rx: Event notification function for the call
+ * @user_call_ID: The tag to attach to the preallocated call
+ * @gfp: The allocation conditions.
+ * @debug_id: The tracing debug ID.
+ *
+ * Charge up the socket with preallocated calls, each with a user ID.  The
+ * ->user_attach_call() callback function should be provided to effect the
+ * attachment from the user's side.  The user is given a ref to hold on the
+ * call.
+ *
+ * Note that the call may be come connected before this function returns.
+ */
+int rxrpc_kernel_charge_accept(struct socket *sock, rxrpc_notify_rx_t notify_rx,
+			       unsigned long user_call_ID, gfp_t gfp,
+			       unsigned int debug_id)
+{
+	struct rxrpc_backlog *b;
+	struct rxrpc_sock *rx;
+	struct sock *sk;
+	int ret;
+
+	sk = sock->sk;
+	rx = rxrpc_sk(sk);
+
+	lock_sock(sk);
+	if (sk->sk_state != RXRPC_SERVER_LISTENING || !rx->backlog) {
+		ret = -ESHUTDOWN;
+		goto out;
+	}
+
+	b = rx->backlog;
+	ret = rxrpc_service_prealloc_one(rx, b, notify_rx, user_call_ID,
+					 gfp, debug_id);
+
+out:
+	release_sock(sk);
+	return ret;
+}
+EXPORT_SYMBOL(rxrpc_kernel_charge_accept);