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, 269 insertions, 0 deletions

diff --git a/drivers/net/arcnet/capmode.c b/drivers/net/arcnet/capmode.c
new file mode 100644
index 000000000..7a0a79973
--- /dev/null
+++ b/drivers/net/arcnet/capmode.c
@@ -0,0 +1,269 @@
+/*
+ * Linux ARCnet driver - "cap mode" packet encapsulation.
+ * It adds sequence numbers to packets for communicating between a user space
+ * application and the driver. After a transmit it sends a packet with protocol
+ * byte 0 back up to the userspace containing the sequence number of the packet
+ * plus the transmit-status on the ArcNet.
+ *
+ * Written 2002-4 by Esben Nielsen, Vestas Wind Systems A/S
+ * Derived from arc-rawmode.c by Avery Pennarun.
+ * arc-rawmode was in turned based on skeleton.c, see below.
+ *
+ * **********************
+ *
+ * The original copyright of skeleton.c was as follows:
+ *
+ * skeleton.c Written 1993 by Donald Becker.
+ * Copyright 1993 United States Government as represented by the
+ * Director, National Security Agency.  This software may only be used
+ * and distributed according to the terms of the GNU General Public License as
+ * modified by SRC, incorporated herein by reference.
+ *
+ * **********************
+ *
+ * For more details, see drivers/net/arcnet.c
+ *
+ * **********************
+ */
+
+#define pr_fmt(fmt) "arcnet:" KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/gfp.h>
+#include <linux/init.h>
+#include <linux/if_arp.h>
+#include <net/arp.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+
+#include "arcdevice.h"
+
+/* packet receiver */
+static void rx(struct net_device *dev, int bufnum,
+	       struct archdr *pkthdr, int length)
+{
+	struct arcnet_local *lp = netdev_priv(dev);
+	struct sk_buff *skb;
+	struct archdr *pkt;
+	char *pktbuf, *pkthdrbuf;
+	int ofs;
+
+	arc_printk(D_DURING, dev, "it's a raw(cap) packet (length=%d)\n",
+		   length);
+
+	if (length >= MinTU)
+		ofs = 512 - length;
+	else
+		ofs = 256 - length;
+
+	skb = alloc_skb(length + ARC_HDR_SIZE + sizeof(int), GFP_ATOMIC);
+	if (!skb) {
+		dev->stats.rx_dropped++;
+		return;
+	}
+	skb_put(skb, length + ARC_HDR_SIZE + sizeof(int));
+	skb->dev = dev;
+	skb_reset_mac_header(skb);
+	pkt = (struct archdr *)skb_mac_header(skb);
+	skb_pull(skb, ARC_HDR_SIZE);
+
+	/* up to sizeof(pkt->soft) has already been copied from the card
+	 * squeeze in an int for the cap encapsulation
+	 * use these variables to be sure we count in bytes, not in
+	 * sizeof(struct archdr)
+	 */
+	pktbuf = (char *)pkt;
+	pkthdrbuf = (char *)pkthdr;
+	memcpy(pktbuf, pkthdrbuf, ARC_HDR_SIZE + sizeof(pkt->soft.cap.proto));
+	memcpy(pktbuf + ARC_HDR_SIZE + sizeof(pkt->soft.cap.proto) + sizeof(int),
+	       pkthdrbuf + ARC_HDR_SIZE + sizeof(pkt->soft.cap.proto),
+	       sizeof(struct archdr) - ARC_HDR_SIZE - sizeof(pkt->soft.cap.proto));
+
+	if (length > sizeof(pkt->soft))
+		lp->hw.copy_from_card(dev, bufnum, ofs + sizeof(pkt->soft),
+				      pkt->soft.raw + sizeof(pkt->soft)
+				      + sizeof(int),
+				      length - sizeof(pkt->soft));
+
+	if (BUGLVL(D_SKB))
+		arcnet_dump_skb(dev, skb, "rx");
+
+	skb->protocol = cpu_to_be16(ETH_P_ARCNET);
+	netif_rx(skb);
+}
+
+/* Create the ARCnet hard/soft headers for cap mode.
+ * There aren't any soft headers in cap mode - not even the protocol id.
+ */
+static int build_header(struct sk_buff *skb,
+			struct net_device *dev,
+			unsigned short type,
+			uint8_t daddr)
+{
+	int hdr_size = ARC_HDR_SIZE;
+	struct archdr *pkt = skb_push(skb, hdr_size);
+
+	arc_printk(D_PROTO, dev, "Preparing header for cap packet %x.\n",
+		   *((int *)&pkt->soft.cap.cookie[0]));
+
+	/* Set the source hardware address.
+	 *
+	 * This is pretty pointless for most purposes, but it can help in
+	 * debugging.  ARCnet does not allow us to change the source address in
+	 * the actual packet sent)
+	 */
+	pkt->hard.source = *dev->dev_addr;
+
+	/* see linux/net/ethernet/eth.c to see where I got the following */
+
+	if (dev->flags & (IFF_LOOPBACK | IFF_NOARP)) {
+		/* FIXME: fill in the last byte of the dest ipaddr here to
+		 * better comply with RFC1051 in "noarp" mode.
+		 */
+		pkt->hard.dest = 0;
+		return hdr_size;
+	}
+	/* otherwise, just fill it in and go! */
+	pkt->hard.dest = daddr;
+
+	return hdr_size;	/* success */
+}
+
+static int prepare_tx(struct net_device *dev, struct archdr *pkt, int length,
+		      int bufnum)
+{
+	struct arcnet_local *lp = netdev_priv(dev);
+	struct arc_hardware *hard = &pkt->hard;
+	int ofs;
+
+	/* hard header is not included in packet length */
+	length -= ARC_HDR_SIZE;
+	/* And neither is the cookie field */
+	length -= sizeof(int);
+
+	arc_printk(D_DURING, dev, "prepare_tx: txbufs=%d/%d/%d\n",
+		   lp->next_tx, lp->cur_tx, bufnum);
+
+	arc_printk(D_PROTO, dev, "Sending for cap packet %x.\n",
+		   *((int *)&pkt->soft.cap.cookie[0]));
+
+	if (length > XMTU) {
+		/* should never happen! other people already check for this. */
+		arc_printk(D_NORMAL, dev, "Bug!  prepare_tx with size %d (> %d)\n",
+			   length, XMTU);
+		length = XMTU;
+	}
+	if (length > MinTU) {
+		hard->offset[0] = 0;
+		hard->offset[1] = ofs = 512 - length;
+	} else if (length > MTU) {
+		hard->offset[0] = 0;
+		hard->offset[1] = ofs = 512 - length - 3;
+	} else {
+		hard->offset[0] = ofs = 256 - length;
+	}
+
+	arc_printk(D_DURING, dev, "prepare_tx: length=%d ofs=%d\n",
+		   length, ofs);
+
+	/* Copy the arcnet-header + the protocol byte down: */
+	lp->hw.copy_to_card(dev, bufnum, 0, hard, ARC_HDR_SIZE);
+	lp->hw.copy_to_card(dev, bufnum, ofs, &pkt->soft.cap.proto,
+			    sizeof(pkt->soft.cap.proto));
+
+	/* Skip the extra integer we have written into it as a cookie
+	 * but write the rest of the message:
+	 */
+	lp->hw.copy_to_card(dev, bufnum, ofs + 1,
+			    ((unsigned char *)&pkt->soft.cap.mes), length - 1);
+
+	lp->lastload_dest = hard->dest;
+
+	return 1;	/* done */
+}
+
+static int ack_tx(struct net_device *dev, int acked)
+{
+	struct arcnet_local *lp = netdev_priv(dev);
+	struct sk_buff *ackskb;
+	struct archdr *ackpkt;
+	int length = sizeof(struct arc_cap);
+
+	arc_printk(D_DURING, dev, "capmode: ack_tx: protocol: %x: result: %d\n",
+		   lp->outgoing.skb->protocol, acked);
+
+	if (BUGLVL(D_SKB))
+		arcnet_dump_skb(dev, lp->outgoing.skb, "ack_tx");
+
+	/* Now alloc a skb to send back up through the layers: */
+	ackskb = alloc_skb(length + ARC_HDR_SIZE, GFP_ATOMIC);
+	if (!ackskb)
+		goto free_outskb;
+
+	skb_put(ackskb, length + ARC_HDR_SIZE);
+	ackskb->dev = dev;
+
+	skb_reset_mac_header(ackskb);
+	ackpkt = (struct archdr *)skb_mac_header(ackskb);
+	/* skb_pull(ackskb, ARC_HDR_SIZE); */
+
+	skb_copy_from_linear_data(lp->outgoing.skb, ackpkt,
+				  ARC_HDR_SIZE + sizeof(struct arc_cap));
+	ackpkt->soft.cap.proto = 0; /* using protocol 0 for acknowledge */
+	ackpkt->soft.cap.mes.ack = acked;
+
+	arc_printk(D_PROTO, dev, "Acknowledge for cap packet %x.\n",
+		   *((int *)&ackpkt->soft.cap.cookie[0]));
+
+	ackskb->protocol = cpu_to_be16(ETH_P_ARCNET);
+
+	if (BUGLVL(D_SKB))
+		arcnet_dump_skb(dev, ackskb, "ack_tx_recv");
+	netif_rx(ackskb);
+
+free_outskb:
+	dev_kfree_skb_irq(lp->outgoing.skb);
+	lp->outgoing.proto = NULL;
+			/* We are always finished when in this protocol */
+
+	return 0;
+}
+
+static struct ArcProto capmode_proto = {
+	.suffix		= 'r',
+	.mtu		= XMTU,
+	.rx		= rx,
+	.build_header	= build_header,
+	.prepare_tx	= prepare_tx,
+	.ack_tx		= ack_tx
+};
+
+static int __init capmode_module_init(void)
+{
+	int count;
+
+	pr_info("cap mode (`c') encapsulation support loaded\n");
+
+	for (count = 1; count <= 8; count++)
+		if (arc_proto_map[count] == arc_proto_default)
+			arc_proto_map[count] = &capmode_proto;
+
+	/* for cap mode, we only set the bcast proto if there's no better one */
+	if (arc_bcast_proto == arc_proto_default)
+		arc_bcast_proto = &capmode_proto;
+
+	arc_proto_default = &capmode_proto;
+	arc_raw_proto = &capmode_proto;
+
+	return 0;
+}
+
+static void __exit capmode_module_exit(void)
+{
+	arcnet_unregister_proto(&capmode_proto);
+}
+module_init(capmode_module_init);
+module_exit(capmode_module_exit);
+
+MODULE_DESCRIPTION("ARCnet CAP mode packet interface module");
+MODULE_LICENSE("GPL");