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, 309 insertions, 0 deletions

diff --git a/net/sunrpc/debugfs.c b/net/sunrpc/debugfs.c
new file mode 100644
index 000000000..32417db34
--- /dev/null
+++ b/net/sunrpc/debugfs.c
@@ -0,0 +1,309 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * debugfs interface for sunrpc
+ *
+ * (c) 2014 Jeff Layton <jlayton@primarydata.com>
+ */
+
+#include <linux/debugfs.h>
+#include <linux/sunrpc/sched.h>
+#include <linux/sunrpc/clnt.h>
+
+#include "netns.h"
+#include "fail.h"
+
+static struct dentry *topdir;
+static struct dentry *rpc_clnt_dir;
+static struct dentry *rpc_xprt_dir;
+
+static int
+tasks_show(struct seq_file *f, void *v)
+{
+	u32 xid = 0;
+	struct rpc_task *task = v;
+	struct rpc_clnt *clnt = task->tk_client;
+	const char *rpc_waitq = "none";
+
+	if (RPC_IS_QUEUED(task))
+		rpc_waitq = rpc_qname(task->tk_waitqueue);
+
+	if (task->tk_rqstp)
+		xid = be32_to_cpu(task->tk_rqstp->rq_xid);
+
+	seq_printf(f, "%5u %04x %6d 0x%x 0x%x %8ld %ps %sv%u %s a:%ps q:%s\n",
+		task->tk_pid, task->tk_flags, task->tk_status,
+		clnt->cl_clid, xid, rpc_task_timeout(task), task->tk_ops,
+		clnt->cl_program->name, clnt->cl_vers, rpc_proc_name(task),
+		task->tk_action, rpc_waitq);
+	return 0;
+}
+
+static void *
+tasks_start(struct seq_file *f, loff_t *ppos)
+	__acquires(&clnt->cl_lock)
+{
+	struct rpc_clnt *clnt = f->private;
+	loff_t pos = *ppos;
+	struct rpc_task *task;
+
+	spin_lock(&clnt->cl_lock);
+	list_for_each_entry(task, &clnt->cl_tasks, tk_task)
+		if (pos-- == 0)
+			return task;
+	return NULL;
+}
+
+static void *
+tasks_next(struct seq_file *f, void *v, loff_t *pos)
+{
+	struct rpc_clnt *clnt = f->private;
+	struct rpc_task *task = v;
+	struct list_head *next = task->tk_task.next;
+
+	++*pos;
+
+	/* If there's another task on list, return it */
+	if (next == &clnt->cl_tasks)
+		return NULL;
+	return list_entry(next, struct rpc_task, tk_task);
+}
+
+static void
+tasks_stop(struct seq_file *f, void *v)
+	__releases(&clnt->cl_lock)
+{
+	struct rpc_clnt *clnt = f->private;
+	spin_unlock(&clnt->cl_lock);
+	seq_printf(f, "clnt[%pISpc] RPC tasks[%d]\n",
+		   (struct sockaddr *)&clnt->cl_xprt->addr,
+		   atomic_read(&clnt->cl_task_count));
+}
+
+static const struct seq_operations tasks_seq_operations = {
+	.start	= tasks_start,
+	.next	= tasks_next,
+	.stop	= tasks_stop,
+	.show	= tasks_show,
+};
+
+static int tasks_open(struct inode *inode, struct file *filp)
+{
+	int ret = seq_open(filp, &tasks_seq_operations);
+	if (!ret) {
+		struct seq_file *seq = filp->private_data;
+		struct rpc_clnt *clnt = seq->private = inode->i_private;
+
+		if (!refcount_inc_not_zero(&clnt->cl_count)) {
+			seq_release(inode, filp);
+			ret = -EINVAL;
+		}
+	}
+
+	return ret;
+}
+
+static int
+tasks_release(struct inode *inode, struct file *filp)
+{
+	struct seq_file *seq = filp->private_data;
+	struct rpc_clnt *clnt = seq->private;
+
+	rpc_release_client(clnt);
+	return seq_release(inode, filp);
+}
+
+static const struct file_operations tasks_fops = {
+	.owner		= THIS_MODULE,
+	.open		= tasks_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= tasks_release,
+};
+
+static int do_xprt_debugfs(struct rpc_clnt *clnt, struct rpc_xprt *xprt, void *numv)
+{
+	int len;
+	char name[24]; /* enough for "../../rpc_xprt/ + 8 hex digits + NULL */
+	char link[9]; /* enough for 8 hex digits + NULL */
+	int *nump = numv;
+
+	if (IS_ERR_OR_NULL(xprt->debugfs))
+		return 0;
+	len = snprintf(name, sizeof(name), "../../rpc_xprt/%s",
+		       xprt->debugfs->d_name.name);
+	if (len >= sizeof(name))
+		return -1;
+	if (*nump == 0)
+		strcpy(link, "xprt");
+	else {
+		len = snprintf(link, sizeof(link), "xprt%d", *nump);
+		if (len >= sizeof(link))
+			return -1;
+	}
+	debugfs_create_symlink(link, clnt->cl_debugfs, name);
+	(*nump)++;
+	return 0;
+}
+
+void
+rpc_clnt_debugfs_register(struct rpc_clnt *clnt)
+{
+	int len;
+	char name[9]; /* enough for 8 hex digits + NULL */
+	int xprtnum = 0;
+
+	len = snprintf(name, sizeof(name), "%x", clnt->cl_clid);
+	if (len >= sizeof(name))
+		return;
+
+	/* make the per-client dir */
+	clnt->cl_debugfs = debugfs_create_dir(name, rpc_clnt_dir);
+
+	/* make tasks file */
+	debugfs_create_file("tasks", S_IFREG | 0400, clnt->cl_debugfs, clnt,
+			    &tasks_fops);
+
+	rpc_clnt_iterate_for_each_xprt(clnt, do_xprt_debugfs, &xprtnum);
+}
+
+void
+rpc_clnt_debugfs_unregister(struct rpc_clnt *clnt)
+{
+	debugfs_remove_recursive(clnt->cl_debugfs);
+	clnt->cl_debugfs = NULL;
+}
+
+static int
+xprt_info_show(struct seq_file *f, void *v)
+{
+	struct rpc_xprt *xprt = f->private;
+
+	seq_printf(f, "netid: %s\n", xprt->address_strings[RPC_DISPLAY_NETID]);
+	seq_printf(f, "addr:  %s\n", xprt->address_strings[RPC_DISPLAY_ADDR]);
+	seq_printf(f, "port:  %s\n", xprt->address_strings[RPC_DISPLAY_PORT]);
+	seq_printf(f, "state: 0x%lx\n", xprt->state);
+	seq_printf(f, "netns: %u\n", xprt->xprt_net->ns.inum);
+
+	if (xprt->ops->get_srcaddr) {
+		int ret, buflen;
+		char buf[INET6_ADDRSTRLEN];
+
+		buflen = ARRAY_SIZE(buf);
+		ret = xprt->ops->get_srcaddr(xprt, buf, buflen);
+		if (ret < 0)
+			ret = sprintf(buf, "<closed>");
+		seq_printf(f, "saddr: %.*s\n", ret, buf);
+	}
+	return 0;
+}
+
+static int
+xprt_info_open(struct inode *inode, struct file *filp)
+{
+	int ret;
+	struct rpc_xprt *xprt = inode->i_private;
+
+	ret = single_open(filp, xprt_info_show, xprt);
+
+	if (!ret) {
+		if (!xprt_get(xprt)) {
+			single_release(inode, filp);
+			ret = -EINVAL;
+		}
+	}
+	return ret;
+}
+
+static int
+xprt_info_release(struct inode *inode, struct file *filp)
+{
+	struct rpc_xprt *xprt = inode->i_private;
+
+	xprt_put(xprt);
+	return single_release(inode, filp);
+}
+
+static const struct file_operations xprt_info_fops = {
+	.owner		= THIS_MODULE,
+	.open		= xprt_info_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= xprt_info_release,
+};
+
+void
+rpc_xprt_debugfs_register(struct rpc_xprt *xprt)
+{
+	int len, id;
+	static atomic_t	cur_id;
+	char		name[9]; /* 8 hex digits + NULL term */
+
+	id = (unsigned int)atomic_inc_return(&cur_id);
+
+	len = snprintf(name, sizeof(name), "%x", id);
+	if (len >= sizeof(name))
+		return;
+
+	/* make the per-client dir */
+	xprt->debugfs = debugfs_create_dir(name, rpc_xprt_dir);
+
+	/* make tasks file */
+	debugfs_create_file("info", S_IFREG | 0400, xprt->debugfs, xprt,
+			    &xprt_info_fops);
+}
+
+void
+rpc_xprt_debugfs_unregister(struct rpc_xprt *xprt)
+{
+	debugfs_remove_recursive(xprt->debugfs);
+	xprt->debugfs = NULL;
+}
+
+#if IS_ENABLED(CONFIG_FAIL_SUNRPC)
+struct fail_sunrpc_attr fail_sunrpc = {
+	.attr			= FAULT_ATTR_INITIALIZER,
+};
+EXPORT_SYMBOL_GPL(fail_sunrpc);
+
+static void fail_sunrpc_init(void)
+{
+	struct dentry *dir;
+
+	dir = fault_create_debugfs_attr("fail_sunrpc", NULL,
+					&fail_sunrpc.attr);
+
+	debugfs_create_bool("ignore-client-disconnect", S_IFREG | 0600, dir,
+			    &fail_sunrpc.ignore_client_disconnect);
+
+	debugfs_create_bool("ignore-server-disconnect", S_IFREG | 0600, dir,
+			    &fail_sunrpc.ignore_server_disconnect);
+
+	debugfs_create_bool("ignore-cache-wait", S_IFREG | 0600, dir,
+			    &fail_sunrpc.ignore_cache_wait);
+}
+#else
+static void fail_sunrpc_init(void)
+{
+}
+#endif
+
+void __exit
+sunrpc_debugfs_exit(void)
+{
+	debugfs_remove_recursive(topdir);
+	topdir = NULL;
+	rpc_clnt_dir = NULL;
+	rpc_xprt_dir = NULL;
+}
+
+void __init
+sunrpc_debugfs_init(void)
+{
+	topdir = debugfs_create_dir("sunrpc", NULL);
+
+	rpc_clnt_dir = debugfs_create_dir("rpc_clnt", topdir);
+
+	rpc_xprt_dir = debugfs_create_dir("rpc_xprt", topdir);
+
+	fail_sunrpc_init();
+}