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, 237 insertions, 0 deletions

diff --git a/fs/afs/main.c b/fs/afs/main.c
new file mode 100644
index 000000000..7a883c599
--- /dev/null
+++ b/fs/afs/main.c
@@ -0,0 +1,237 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* AFS client file system
+ *
+ * Copyright (C) 2002,5 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/init.h>
+#include <linux/completion.h>
+#include <linux/sched.h>
+#include <linux/random.h>
+#include <linux/proc_fs.h>
+#define CREATE_TRACE_POINTS
+#include "internal.h"
+
+MODULE_DESCRIPTION("AFS Client File System");
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");
+
+unsigned afs_debug;
+module_param_named(debug, afs_debug, uint, S_IWUSR | S_IRUGO);
+MODULE_PARM_DESC(debug, "AFS debugging mask");
+
+static char *rootcell;
+
+module_param(rootcell, charp, 0);
+MODULE_PARM_DESC(rootcell, "root AFS cell name and VL server IP addr list");
+
+struct workqueue_struct *afs_wq;
+static struct proc_dir_entry *afs_proc_symlink;
+
+#if defined(CONFIG_ALPHA)
+const char afs_init_sysname[] = "alpha_linux26";
+#elif defined(CONFIG_X86_64)
+const char afs_init_sysname[] = "amd64_linux26";
+#elif defined(CONFIG_ARM)
+const char afs_init_sysname[] = "arm_linux26";
+#elif defined(CONFIG_ARM64)
+const char afs_init_sysname[] = "aarch64_linux26";
+#elif defined(CONFIG_X86_32)
+const char afs_init_sysname[] = "i386_linux26";
+#elif defined(CONFIG_PPC64)
+const char afs_init_sysname[] = "ppc64_linux26";
+#elif defined(CONFIG_PPC32)
+const char afs_init_sysname[] = "ppc_linux26";
+#elif defined(CONFIG_S390)
+#ifdef CONFIG_64BIT
+const char afs_init_sysname[] = "s390x_linux26";
+#else
+const char afs_init_sysname[] = "s390_linux26";
+#endif
+#elif defined(CONFIG_SPARC64)
+const char afs_init_sysname[] = "sparc64_linux26";
+#elif defined(CONFIG_SPARC32)
+const char afs_init_sysname[] = "sparc_linux26";
+#else
+const char afs_init_sysname[] = "unknown_linux26";
+#endif
+
+/*
+ * Initialise an AFS network namespace record.
+ */
+static int __net_init afs_net_init(struct net *net_ns)
+{
+	struct afs_sysnames *sysnames;
+	struct afs_net *net = afs_net(net_ns);
+	int ret;
+
+	net->net = net_ns;
+	net->live = true;
+	generate_random_uuid((unsigned char *)&net->uuid);
+
+	INIT_WORK(&net->charge_preallocation_work, afs_charge_preallocation);
+	INIT_WORK(&net->rx_oob_work, afs_process_oob_queue);
+	mutex_init(&net->socket_mutex);
+
+	net->cells = RB_ROOT;
+	idr_init(&net->cells_dyn_ino);
+	init_rwsem(&net->cells_lock);
+	mutex_init(&net->cells_alias_lock);
+	mutex_init(&net->proc_cells_lock);
+	INIT_HLIST_HEAD(&net->proc_cells);
+
+	seqlock_init(&net->fs_lock);
+	INIT_LIST_HEAD(&net->fs_probe_fast);
+	INIT_LIST_HEAD(&net->fs_probe_slow);
+	INIT_HLIST_HEAD(&net->fs_proc);
+
+	INIT_WORK(&net->fs_prober, afs_fs_probe_dispatcher);
+	timer_setup(&net->fs_probe_timer, afs_fs_probe_timer, 0);
+	atomic_set(&net->servers_outstanding, 1);
+
+	ret = -ENOMEM;
+	sysnames = kzalloc_obj(*sysnames);
+	if (!sysnames)
+		goto error_sysnames;
+	sysnames->subs[0] = (char *)&afs_init_sysname;
+	sysnames->nr = 1;
+	refcount_set(&sysnames->usage, 1);
+	net->sysnames = sysnames;
+	rwlock_init(&net->sysnames_lock);
+
+	/* Register the /proc stuff */
+	ret = afs_proc_init(net);
+	if (ret < 0)
+		goto error_proc;
+
+	/* Initialise the cell DB */
+	ret = afs_cell_init(net, rootcell);
+	if (ret < 0)
+		goto error_cell_init;
+
+	/* Create the RxRPC transport */
+	ret = afs_open_socket(net);
+	if (ret < 0)
+		goto error_open_socket;
+
+	return 0;
+
+error_open_socket:
+	net->live = false;
+	afs_fs_probe_cleanup(net);
+	afs_cell_purge(net);
+	afs_wait_for_servers(net);
+error_cell_init:
+	net->live = false;
+	afs_proc_cleanup(net);
+error_proc:
+	afs_put_sysnames(net->sysnames);
+error_sysnames:
+	idr_destroy(&net->cells_dyn_ino);
+	net->live = false;
+	return ret;
+}
+
+/*
+ * Clean up and destroy an AFS network namespace record.
+ */
+static void __net_exit afs_net_exit(struct net *net_ns)
+{
+	struct afs_net *net = afs_net(net_ns);
+
+	net->live = false;
+	afs_fs_probe_cleanup(net);
+	afs_cell_purge(net);
+	afs_wait_for_servers(net);
+	afs_close_socket(net);
+	afs_proc_cleanup(net);
+	afs_put_sysnames(net->sysnames);
+	idr_destroy(&net->cells_dyn_ino);
+	kfree_rcu(rcu_access_pointer(net->address_prefs), rcu);
+}
+
+static struct pernet_operations afs_net_ops = {
+	.init	= afs_net_init,
+	.exit	= afs_net_exit,
+	.id	= &afs_net_id,
+	.size	= sizeof(struct afs_net),
+};
+
+/*
+ * initialise the AFS client FS module
+ */
+static int __init afs_init(void)
+{
+	int ret = -ENOMEM;
+
+	printk(KERN_INFO "kAFS: Red Hat AFS client v0.1 registering.\n");
+
+	afs_wq = alloc_workqueue("afs", WQ_PERCPU, 0);
+	if (!afs_wq)
+		goto error_afs_wq;
+	afs_async_calls = alloc_workqueue("kafsd", WQ_MEM_RECLAIM | WQ_UNBOUND, 0);
+	if (!afs_async_calls)
+		goto error_async;
+	afs_lock_manager = alloc_workqueue("kafs_lockd", WQ_MEM_RECLAIM | WQ_PERCPU, 0);
+	if (!afs_lock_manager)
+		goto error_lockmgr;
+
+	ret = register_pernet_device(&afs_net_ops);
+	if (ret < 0)
+		goto error_net;
+
+	/* register the filesystems */
+	ret = afs_fs_init();
+	if (ret < 0)
+		goto error_fs;
+
+	afs_proc_symlink = proc_symlink("fs/afs", NULL, "../self/net/afs");
+	if (!afs_proc_symlink) {
+		ret = -ENOMEM;
+		goto error_proc;
+	}
+
+	return ret;
+
+error_proc:
+	afs_fs_exit();
+error_fs:
+	unregister_pernet_device(&afs_net_ops);
+error_net:
+	destroy_workqueue(afs_lock_manager);
+error_lockmgr:
+	destroy_workqueue(afs_async_calls);
+error_async:
+	destroy_workqueue(afs_wq);
+error_afs_wq:
+	rcu_barrier();
+	printk(KERN_ERR "kAFS: failed to register: %d\n", ret);
+	return ret;
+}
+
+/* XXX late_initcall is kludgy, but the only alternative seems to create
+ * a transport upon the first mount, which is worse. Or is it?
+ */
+late_initcall(afs_init);	/* must be called after net/ to create socket */
+
+/*
+ * clean up on module removal
+ */
+static void __exit afs_exit(void)
+{
+	printk(KERN_INFO "kAFS: Red Hat AFS client v0.1 unregistering.\n");
+
+	proc_remove(afs_proc_symlink);
+	afs_fs_exit();
+	unregister_pernet_device(&afs_net_ops);
+	destroy_workqueue(afs_lock_manager);
+	destroy_workqueue(afs_async_calls);
+	destroy_workqueue(afs_wq);
+	afs_clean_up_permit_cache();
+	rcu_barrier();
+}
+
+module_exit(afs_exit);