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, 270 insertions, 0 deletions

diff --git a/fs/smb/server/proc.c b/fs/smb/server/proc.c
new file mode 100644
index 000000000..826353ed0
--- /dev/null
+++ b/fs/smb/server/proc.c
@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   Copyright (C) 2025, LG Electronics.
+ *   Author(s): Hyunchul Lee <hyc.lee@gmail.com>
+ *   Copyright (C) 2025, Samsung Electronics.
+ *   Author(s): Vedansh Bhardwaj <v.bhardwaj@samsung.com>
+ */
+
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+
+#include "misc.h"
+#include "connection.h"
+#include "server.h"
+#include "stats.h"
+#include "smb_common.h"
+#include "smb2pdu.h"
+#include "vfs_cache.h"
+
+static struct proc_dir_entry *ksmbd_proc_fs;
+struct ksmbd_counters ksmbd_counters;
+
+struct proc_dir_entry *ksmbd_proc_create(const char *name,
+					 int (*show)(struct seq_file *m, void *v),
+						 void *v)
+{
+	return proc_create_single_data(name, 0400, ksmbd_proc_fs,
+			   show, v);
+}
+
+void ksmbd_proc_show_flag_names(struct seq_file *m,
+				const struct ksmbd_const_name *table,
+				int count, unsigned int flags)
+{
+	unsigned int remaining = flags;
+	bool separator = false;
+	int i;
+
+	for (i = 0; i < count; i++) {
+		unsigned int flag = table[i].const_value;
+
+		if (!flag || (remaining & flag) != flag)
+			continue;
+		seq_printf(m, "%s%s", separator ? "," : "", table[i].name);
+		separator = true;
+		remaining &= ~flag;
+	}
+
+	if (remaining)
+		seq_printf(m, "%s0x%08x", separator ? "," : "", remaining);
+	else if (!separator)
+		seq_puts(m, "none");
+}
+
+const char *ksmbd_proc_const_name(const struct ksmbd_const_name *table,
+				  int count, unsigned int const_value)
+{
+	int i;
+
+	for (i = 0; i < count; i++) {
+		if (table[i].const_value == const_value)
+			return table[i].name;
+	}
+	return NULL;
+}
+
+struct ksmbd_const_smb2_process_req {
+	unsigned int const_value;
+	const char *name;
+};
+
+static const struct ksmbd_const_smb2_process_req smb2_process_req[KSMBD_COUNTER_MAX_REQS] = {
+	{le16_to_cpu(SMB2_NEGOTIATE), "SMB2_NEGOTIATE"},
+	{le16_to_cpu(SMB2_SESSION_SETUP), "SMB2_SESSION_SETUP"},
+	{le16_to_cpu(SMB2_LOGOFF), "SMB2_LOGOFF"},
+	{le16_to_cpu(SMB2_TREE_CONNECT), "SMB2_TREE_CONNECT"},
+	{le16_to_cpu(SMB2_TREE_DISCONNECT), "SMB2_TREE_DISCONNECT"},
+	{le16_to_cpu(SMB2_CREATE), "SMB2_CREATE"},
+	{le16_to_cpu(SMB2_CLOSE), "SMB2_CLOSE"},
+	{le16_to_cpu(SMB2_FLUSH), "SMB2_FLUSH"},
+	{le16_to_cpu(SMB2_READ), "SMB2_READ"},
+	{le16_to_cpu(SMB2_WRITE), "SMB2_WRITE"},
+	{le16_to_cpu(SMB2_LOCK), "SMB2_LOCK"},
+	{le16_to_cpu(SMB2_IOCTL), "SMB2_IOCTL"},
+	{le16_to_cpu(SMB2_CANCEL), "SMB2_CANCEL"},
+	{le16_to_cpu(SMB2_ECHO), "SMB2_ECHO"},
+	{le16_to_cpu(SMB2_QUERY_DIRECTORY), "SMB2_QUERY_DIRECTORY"},
+	{le16_to_cpu(SMB2_CHANGE_NOTIFY), "SMB2_CHANGE_NOTIFY"},
+	{le16_to_cpu(SMB2_QUERY_INFO), "SMB2_QUERY_INFO"},
+	{le16_to_cpu(SMB2_SET_INFO), "SMB2_SET_INFO"},
+	{le16_to_cpu(SMB2_OPLOCK_BREAK), "SMB2_OPLOCK_BREAK"},
+};
+
+static const char *ksmbd_server_state_string(void)
+{
+	switch (READ_ONCE(server_conf.state)) {
+	case SERVER_STATE_STARTING_UP:
+		return "starting";
+	case SERVER_STATE_RUNNING:
+		return "running";
+	case SERVER_STATE_RESETTING:
+		return "resetting";
+	case SERVER_STATE_SHUTTING_DOWN:
+		return "shutdown";
+	default:
+		return "unknown";
+	}
+}
+
+static const char *ksmbd_signing_mode_string(void)
+{
+	switch (server_conf.signing) {
+	case KSMBD_CONFIG_OPT_DISABLED:
+		return "disabled";
+	case KSMBD_CONFIG_OPT_MANDATORY:
+		return "mandatory";
+	case KSMBD_CONFIG_OPT_AUTO:
+		return "auto";
+	default:
+		return "unknown";
+	}
+}
+
+static void proc_show_runtime_totals(struct seq_file *m)
+{
+	struct ksmbd_conn *conn;
+	unsigned int clients = 0;
+	unsigned int open_files = 0;
+	int i;
+
+	down_read(&conn_list_lock);
+	hash_for_each(conn_list, i, conn, hlist) {
+		clients++;
+		open_files += atomic_read(&conn->stats.open_files_count);
+	}
+	up_read(&conn_list_lock);
+
+	seq_printf(m, "clients:\t%u\n", clients);
+	seq_printf(m, "open_files:\t%u\n", open_files);
+}
+
+static int proc_show_ksmbd_stats(struct seq_file *m, void *v)
+{
+	int i;
+
+	seq_puts(m, "Server\n");
+	seq_printf(m, "state:\t%s\n", ksmbd_server_state_string());
+	seq_printf(m, "name:\t%s\n", ksmbd_server_string());
+	seq_printf(m, "netbios:\t%s\n", ksmbd_netbios_name());
+	seq_printf(m, "work_group:\t%s\n", ksmbd_work_group());
+	seq_printf(m, "min_protocol:\t%s\n", ksmbd_get_protocol_string(server_conf.min_protocol));
+	seq_printf(m, "max_protocol:\t%s\n", ksmbd_get_protocol_string(server_conf.max_protocol));
+	seq_printf(m, "flags:\t0x%08x\n", server_conf.flags);
+	seq_printf(m, "tcp_port:\t%u\n", server_conf.tcp_port);
+	seq_printf(m, "signing:\t%s\n", ksmbd_signing_mode_string());
+	seq_printf(m, "signing_enforced:\t%s\n",
+		   server_conf.enforced_signing ? "yes" : "no");
+	seq_printf(m, "bind_interfaces_only:\t%s\n",
+		   server_conf.bind_interfaces_only ? "yes" : "no");
+	seq_printf(m, "max_connections:\t%u\n", server_conf.max_connections);
+	seq_printf(m, "max_connections_per_ip:\t%u\n",
+		   server_conf.max_ip_connections);
+	seq_printf(m, "max_inflight_requests:\t%u\n",
+		   server_conf.max_inflight_req);
+	seq_printf(m, "deadtime_seconds:\t%lu\n", server_conf.deadtime / HZ);
+	seq_printf(m, "ipc_timeout_seconds:\t%u\n", server_conf.ipc_timeout / HZ);
+	if (server_conf.ipc_last_active)
+		seq_printf(m, "ipc_last_active_seconds:\t%lu\n",
+			   jiffies_to_msecs(jiffies - server_conf.ipc_last_active) /
+			   MSEC_PER_SEC);
+	else
+		seq_puts(m, "ipc_last_active_seconds:\tnever\n");
+	seq_printf(m, "durable_scavenger:\t%s\n",
+		   ksmbd_durable_scavenger_active() ? "running" : "stopped");
+	seq_printf(m, "share_fake_fscaps:\t0x%08x\n",
+		   server_conf.share_fake_fscaps);
+	proc_show_runtime_totals(m);
+	seq_printf(m, "sessions:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_SESSIONS));
+	seq_printf(m, "tree_connects:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_TREE_CONNS));
+	seq_printf(m, "requests:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_REQUESTS));
+	seq_printf(m, "read_bytes:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_READ_BYTES));
+	seq_printf(m, "written_bytes:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_WRITE_BYTES));
+
+	seq_puts(m, "\nSMB2\n");
+	for (i = 0; i < KSMBD_COUNTER_MAX_REQS; i++)
+		seq_printf(m, "%s:\t%lld\n", smb2_process_req[i].name,
+			   ksmbd_counter_sum(KSMBD_COUNTER_FIRST_REQ + i));
+
+	seq_puts(m, "\nSMB2 status\n");
+	seq_printf(m, "success:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_STATUS_SUCCESS));
+	seq_printf(m, "informational:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_STATUS_INFORMATIONAL));
+	seq_printf(m, "warning:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_STATUS_WARNING));
+	seq_printf(m, "error:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_STATUS_ERROR));
+	seq_printf(m, "access_denied:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_ERROR_ACCESS_DENIED));
+	seq_printf(m, "not_found:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_ERROR_NOT_FOUND));
+	seq_printf(m, "invalid_parameter:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_ERROR_INVALID_PARAMETER));
+	seq_printf(m, "sharing_violation:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_ERROR_SHARING_VIOLATION));
+	seq_printf(m, "not_supported:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_ERROR_NOT_SUPPORTED));
+	seq_printf(m, "other:\t%lld\n",
+		   ksmbd_counter_sum(KSMBD_COUNTER_ERROR_OTHER));
+	return 0;
+}
+
+void ksmbd_proc_cleanup(void)
+{
+	int i;
+
+	if (!ksmbd_proc_fs)
+		return;
+
+	proc_remove(ksmbd_proc_fs);
+
+	for (i = 0; i < ARRAY_SIZE(ksmbd_counters.counters); i++)
+		percpu_counter_destroy(&ksmbd_counters.counters[i]);
+
+	ksmbd_proc_fs = NULL;
+}
+
+void ksmbd_proc_reset(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(ksmbd_counters.counters); i++)
+		percpu_counter_set(&ksmbd_counters.counters[i], 0);
+}
+
+int ksmbd_proc_init(void)
+{
+	int i;
+	int retval = -ENOMEM;
+
+	ksmbd_proc_fs = proc_mkdir("fs/ksmbd", NULL);
+	if (!ksmbd_proc_fs)
+		return retval;
+
+	if (!proc_mkdir_mode("sessions", 0400, ksmbd_proc_fs))
+		goto err_out;
+
+	for (i = 0; i < ARRAY_SIZE(ksmbd_counters.counters); i++) {
+		retval = percpu_counter_init(&ksmbd_counters.counters[i], 0, GFP_KERNEL);
+		if (retval)
+			goto err_out;
+	}
+
+	if (!ksmbd_proc_create("server", proc_show_ksmbd_stats, NULL)) {
+		retval = -ENOMEM;
+		goto err_out;
+	}
+
+	ksmbd_proc_reset();
+	return 0;
+err_out:
+	ksmbd_proc_cleanup();
+	return retval;
+}