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, 281 insertions, 0 deletions

diff --git a/net/ethtool/tunnels.c b/net/ethtool/tunnels.c
new file mode 100644
index 000000000..b4ce47dd2
--- /dev/null
+++ b/net/ethtool/tunnels.c
@@ -0,0 +1,281 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/ethtool_netlink.h>
+#include <net/udp_tunnel.h>
+#include <net/vxlan.h>
+
+#include "bitset.h"
+#include "common.h"
+#include "netlink.h"
+
+const struct nla_policy ethnl_tunnel_info_get_policy[] = {
+	[ETHTOOL_A_TUNNEL_INFO_HEADER]		=
+		NLA_POLICY_NESTED(ethnl_header_policy),
+};
+
+static_assert(ETHTOOL_UDP_TUNNEL_TYPE_VXLAN == ilog2(UDP_TUNNEL_TYPE_VXLAN));
+static_assert(ETHTOOL_UDP_TUNNEL_TYPE_GENEVE == ilog2(UDP_TUNNEL_TYPE_GENEVE));
+static_assert(ETHTOOL_UDP_TUNNEL_TYPE_VXLAN_GPE ==
+	      ilog2(UDP_TUNNEL_TYPE_VXLAN_GPE));
+
+static ssize_t ethnl_udp_table_reply_size(unsigned int types, bool compact)
+{
+	ssize_t size;
+
+	size = ethnl_bitset32_size(&types, NULL, __ETHTOOL_UDP_TUNNEL_TYPE_CNT,
+				   udp_tunnel_type_names, compact);
+	if (size < 0)
+		return size;
+
+	return size +
+		nla_total_size(0) + /* _UDP_TABLE */
+		nla_total_size(sizeof(u32)); /* _UDP_TABLE_SIZE */
+}
+
+static ssize_t
+ethnl_tunnel_info_reply_size(const struct ethnl_req_info *req_base,
+			     struct netlink_ext_ack *extack)
+{
+	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+	const struct udp_tunnel_nic_info *info;
+	unsigned int i;
+	ssize_t ret;
+	size_t size;
+
+	info = req_base->dev->udp_tunnel_nic_info;
+	if (!info) {
+		NL_SET_ERR_MSG(extack,
+			       "device does not report tunnel offload info");
+		return -EOPNOTSUPP;
+	}
+
+	size =	nla_total_size(0); /* _INFO_UDP_PORTS */
+
+	for (i = 0; i < UDP_TUNNEL_NIC_MAX_TABLES; i++) {
+		if (!info->tables[i].n_entries)
+			break;
+
+		ret = ethnl_udp_table_reply_size(info->tables[i].tunnel_types,
+						 compact);
+		if (ret < 0)
+			return ret;
+		size += ret;
+
+		size += udp_tunnel_nic_dump_size(req_base->dev, i);
+	}
+
+	if (info->flags & UDP_TUNNEL_NIC_INFO_STATIC_IANA_VXLAN) {
+		ret = ethnl_udp_table_reply_size(0, compact);
+		if (ret < 0)
+			return ret;
+		size += ret;
+
+		size += nla_total_size(0) +		 /* _TABLE_ENTRY */
+			nla_total_size(sizeof(__be16)) + /* _ENTRY_PORT */
+			nla_total_size(sizeof(u32));	 /* _ENTRY_TYPE */
+	}
+
+	return size;
+}
+
+static int
+ethnl_tunnel_info_fill_reply(const struct ethnl_req_info *req_base,
+			     struct sk_buff *skb)
+{
+	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+	const struct udp_tunnel_nic_info *info;
+	struct nlattr *ports, *table, *entry;
+	unsigned int i;
+
+	info = req_base->dev->udp_tunnel_nic_info;
+	if (!info)
+		return -EOPNOTSUPP;
+
+	ports = nla_nest_start(skb, ETHTOOL_A_TUNNEL_INFO_UDP_PORTS);
+	if (!ports)
+		return -EMSGSIZE;
+
+	for (i = 0; i < UDP_TUNNEL_NIC_MAX_TABLES; i++) {
+		if (!info->tables[i].n_entries)
+			break;
+
+		table = nla_nest_start(skb, ETHTOOL_A_TUNNEL_UDP_TABLE);
+		if (!table)
+			goto err_cancel_ports;
+
+		if (nla_put_u32(skb, ETHTOOL_A_TUNNEL_UDP_TABLE_SIZE,
+				info->tables[i].n_entries))
+			goto err_cancel_table;
+
+		if (ethnl_put_bitset32(skb, ETHTOOL_A_TUNNEL_UDP_TABLE_TYPES,
+				       &info->tables[i].tunnel_types, NULL,
+				       __ETHTOOL_UDP_TUNNEL_TYPE_CNT,
+				       udp_tunnel_type_names, compact))
+			goto err_cancel_table;
+
+		if (udp_tunnel_nic_dump_write(req_base->dev, i, skb))
+			goto err_cancel_table;
+
+		nla_nest_end(skb, table);
+	}
+
+	if (info->flags & UDP_TUNNEL_NIC_INFO_STATIC_IANA_VXLAN) {
+		u32 zero = 0;
+
+		table = nla_nest_start(skb, ETHTOOL_A_TUNNEL_UDP_TABLE);
+		if (!table)
+			goto err_cancel_ports;
+
+		if (nla_put_u32(skb, ETHTOOL_A_TUNNEL_UDP_TABLE_SIZE, 1))
+			goto err_cancel_table;
+
+		if (ethnl_put_bitset32(skb, ETHTOOL_A_TUNNEL_UDP_TABLE_TYPES,
+				       &zero, NULL,
+				       __ETHTOOL_UDP_TUNNEL_TYPE_CNT,
+				       udp_tunnel_type_names, compact))
+			goto err_cancel_table;
+
+		entry = nla_nest_start(skb, ETHTOOL_A_TUNNEL_UDP_TABLE_ENTRY);
+		if (!entry)
+			goto err_cancel_entry;
+
+		if (nla_put_be16(skb, ETHTOOL_A_TUNNEL_UDP_ENTRY_PORT,
+				 htons(IANA_VXLAN_UDP_PORT)) ||
+		    nla_put_u32(skb, ETHTOOL_A_TUNNEL_UDP_ENTRY_TYPE,
+				ilog2(UDP_TUNNEL_TYPE_VXLAN)))
+			goto err_cancel_entry;
+
+		nla_nest_end(skb, entry);
+		nla_nest_end(skb, table);
+	}
+
+	nla_nest_end(skb, ports);
+
+	return 0;
+
+err_cancel_entry:
+	nla_nest_cancel(skb, entry);
+err_cancel_table:
+	nla_nest_cancel(skb, table);
+err_cancel_ports:
+	nla_nest_cancel(skb, ports);
+	return -EMSGSIZE;
+}
+
+int ethnl_tunnel_info_doit(struct sk_buff *skb, struct genl_info *info)
+{
+	struct ethnl_req_info req_info = {};
+	struct nlattr **tb = info->attrs;
+	struct sk_buff *rskb;
+	void *reply_payload;
+	int reply_len;
+	int ret;
+
+	ret = ethnl_parse_header_dev_get(&req_info,
+					 tb[ETHTOOL_A_TUNNEL_INFO_HEADER],
+					 genl_info_net(info), info->extack,
+					 true);
+	if (ret < 0)
+		return ret;
+
+	rtnl_lock();
+	ret = ethnl_tunnel_info_reply_size(&req_info, info->extack);
+	if (ret < 0)
+		goto err_unlock_rtnl;
+	reply_len = ret + ethnl_reply_header_size();
+
+	rskb = ethnl_reply_init(reply_len, req_info.dev,
+				ETHTOOL_MSG_TUNNEL_INFO_GET_REPLY,
+				ETHTOOL_A_TUNNEL_INFO_HEADER,
+				info, &reply_payload);
+	if (!rskb) {
+		ret = -ENOMEM;
+		goto err_unlock_rtnl;
+	}
+
+	ret = ethnl_tunnel_info_fill_reply(&req_info, rskb);
+	if (ret)
+		goto err_free_msg;
+	rtnl_unlock();
+	ethnl_parse_header_dev_put(&req_info);
+	genlmsg_end(rskb, reply_payload);
+
+	return genlmsg_reply(rskb, info);
+
+err_free_msg:
+	nlmsg_free(rskb);
+err_unlock_rtnl:
+	rtnl_unlock();
+	ethnl_parse_header_dev_put(&req_info);
+	return ret;
+}
+
+struct ethnl_tunnel_info_dump_ctx {
+	struct ethnl_req_info	req_info;
+	unsigned long		ifindex;
+};
+
+int ethnl_tunnel_info_start(struct netlink_callback *cb)
+{
+	const struct genl_dumpit_info *info = genl_dumpit_info(cb);
+	struct ethnl_tunnel_info_dump_ctx *ctx = (void *)cb->ctx;
+	struct nlattr **tb = info->info.attrs;
+	int ret;
+
+	BUILD_BUG_ON(sizeof(*ctx) > sizeof(cb->ctx));
+
+	memset(ctx, 0, sizeof(*ctx));
+
+	ret = ethnl_parse_header_dev_get(&ctx->req_info,
+					 tb[ETHTOOL_A_TUNNEL_INFO_HEADER],
+					 sock_net(cb->skb->sk), cb->extack,
+					 false);
+	if (ctx->req_info.dev) {
+		ethnl_parse_header_dev_put(&ctx->req_info);
+		ctx->req_info.dev = NULL;
+	}
+
+	return ret;
+}
+
+int ethnl_tunnel_info_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
+{
+	struct ethnl_tunnel_info_dump_ctx *ctx = (void *)cb->ctx;
+	struct net *net = sock_net(skb->sk);
+	struct net_device *dev;
+	int ret = 0;
+	void *ehdr;
+
+	rtnl_lock();
+	for_each_netdev_dump(net, dev, ctx->ifindex) {
+		ehdr = ethnl_dump_put(skb, cb,
+				      ETHTOOL_MSG_TUNNEL_INFO_GET_REPLY);
+		if (!ehdr) {
+			ret = -EMSGSIZE;
+			break;
+		}
+
+		ret = ethnl_fill_reply_header(skb, dev,
+					      ETHTOOL_A_TUNNEL_INFO_HEADER);
+		if (ret < 0) {
+			genlmsg_cancel(skb, ehdr);
+			break;
+		}
+
+		ctx->req_info.dev = dev;
+		ret = ethnl_tunnel_info_fill_reply(&ctx->req_info, skb);
+		ctx->req_info.dev = NULL;
+		if (ret < 0) {
+			genlmsg_cancel(skb, ehdr);
+			if (ret == -EOPNOTSUPP)
+				continue;
+			break;
+		}
+		genlmsg_end(skb, ehdr);
+	}
+	rtnl_unlock();
+
+	if (ret == -EMSGSIZE && skb->len)
+		return skb->len;
+	return ret;
+}