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, 377 insertions, 0 deletions

diff --git a/fs/afs/fs_operation.c b/fs/afs/fs_operation.c
new file mode 100644
index 000000000..20801b295
--- /dev/null
+++ b/fs/afs/fs_operation.c
@@ -0,0 +1,377 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Fileserver-directed operation handling.
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include "internal.h"
+
+static atomic_t afs_operation_debug_counter;
+
+/*
+ * Create an operation against a volume.
+ */
+struct afs_operation *afs_alloc_operation(struct key *key, struct afs_volume *volume)
+{
+	struct afs_operation *op;
+
+	_enter("");
+
+	op = kzalloc_obj(*op);
+	if (!op)
+		return ERR_PTR(-ENOMEM);
+
+	if (!key) {
+		key = afs_request_key(volume->cell);
+		if (IS_ERR(key)) {
+			kfree(op);
+			return ERR_CAST(key);
+		}
+	} else {
+		key_get(key);
+	}
+
+	op->key			= key;
+	op->volume		= afs_get_volume(volume, afs_volume_trace_get_new_op);
+	op->net			= volume->cell->net;
+	op->cb_v_break		= atomic_read(&volume->cb_v_break);
+	op->pre_volsync.creation = volume->creation_time;
+	op->pre_volsync.update	= volume->update_time;
+	op->debug_id		= atomic_inc_return(&afs_operation_debug_counter);
+	op->nr_iterations	= -1;
+	afs_op_set_error(op, -EDESTADDRREQ);
+
+	_leave(" = [op=%08x]", op->debug_id);
+	return op;
+}
+
+struct afs_io_locker {
+	struct list_head	link;
+	struct task_struct	*task;
+	unsigned long		have_lock;
+};
+
+/*
+ * Unlock the I/O lock on a vnode.
+ */
+static void afs_unlock_for_io(struct afs_vnode *vnode)
+{
+	struct afs_io_locker *locker;
+
+	spin_lock(&vnode->lock);
+	locker = list_first_entry_or_null(&vnode->io_lock_waiters,
+					  struct afs_io_locker, link);
+	if (locker) {
+		list_del(&locker->link);
+		smp_store_release(&locker->have_lock, 1); /* The unlock barrier. */
+		smp_mb__after_atomic(); /* Store have_lock before task state */
+		wake_up_process(locker->task);
+	} else {
+		clear_bit(AFS_VNODE_IO_LOCK, &vnode->flags);
+	}
+	spin_unlock(&vnode->lock);
+}
+
+/*
+ * Lock the I/O lock on a vnode uninterruptibly.  We can't use an ordinary
+ * mutex as lockdep will complain if we unlock it in the wrong thread.
+ */
+static void afs_lock_for_io(struct afs_vnode *vnode)
+{
+	struct afs_io_locker myself = { .task = current, };
+
+	spin_lock(&vnode->lock);
+
+	if (!test_and_set_bit(AFS_VNODE_IO_LOCK, &vnode->flags)) {
+		spin_unlock(&vnode->lock);
+		return;
+	}
+
+	list_add_tail(&myself.link, &vnode->io_lock_waiters);
+	spin_unlock(&vnode->lock);
+
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (smp_load_acquire(&myself.have_lock)) /* The lock barrier */
+			break;
+		schedule();
+	}
+	__set_current_state(TASK_RUNNING);
+}
+
+/*
+ * Lock the I/O lock on a vnode interruptibly.  We can't use an ordinary mutex
+ * as lockdep will complain if we unlock it in the wrong thread.
+ */
+static int afs_lock_for_io_interruptible(struct afs_vnode *vnode)
+{
+	struct afs_io_locker myself = { .task = current, };
+	int ret = 0;
+
+	spin_lock(&vnode->lock);
+
+	if (!test_and_set_bit(AFS_VNODE_IO_LOCK, &vnode->flags)) {
+		spin_unlock(&vnode->lock);
+		return 0;
+	}
+
+	list_add_tail(&myself.link, &vnode->io_lock_waiters);
+	spin_unlock(&vnode->lock);
+
+	for (;;) {
+		set_current_state(TASK_INTERRUPTIBLE);
+		if (smp_load_acquire(&myself.have_lock) || /* The lock barrier */
+		    signal_pending(current))
+			break;
+		schedule();
+	}
+	__set_current_state(TASK_RUNNING);
+
+	/* If we got a signal, try to transfer the lock onto the next
+	 * waiter.
+	 */
+	if (unlikely(signal_pending(current))) {
+		spin_lock(&vnode->lock);
+		if (myself.have_lock) {
+			spin_unlock(&vnode->lock);
+			afs_unlock_for_io(vnode);
+		} else {
+			list_del(&myself.link);
+			spin_unlock(&vnode->lock);
+		}
+		ret = -ERESTARTSYS;
+	}
+	return ret;
+}
+
+/*
+ * Lock the vnode(s) being operated upon.
+ */
+static bool afs_get_io_locks(struct afs_operation *op)
+{
+	struct afs_vnode *vnode = op->file[0].vnode;
+	struct afs_vnode *vnode2 = op->file[1].vnode;
+
+	_enter("");
+
+	if (op->flags & AFS_OPERATION_UNINTR) {
+		afs_lock_for_io(vnode);
+		op->flags |= AFS_OPERATION_LOCK_0;
+		_leave(" = t [1]");
+		return true;
+	}
+
+	if (!vnode2 || !op->file[1].need_io_lock || vnode == vnode2)
+		vnode2 = NULL;
+
+	if (vnode2 > vnode)
+		swap(vnode, vnode2);
+
+	if (afs_lock_for_io_interruptible(vnode) < 0) {
+		afs_op_set_error(op, -ERESTARTSYS);
+		op->flags |= AFS_OPERATION_STOP;
+		_leave(" = f [I 0]");
+		return false;
+	}
+	op->flags |= AFS_OPERATION_LOCK_0;
+
+	if (vnode2) {
+		if (afs_lock_for_io_interruptible(vnode2) < 0) {
+			afs_op_set_error(op, -ERESTARTSYS);
+			op->flags |= AFS_OPERATION_STOP;
+			afs_unlock_for_io(vnode);
+			op->flags &= ~AFS_OPERATION_LOCK_0;
+			_leave(" = f [I 1]");
+			return false;
+		}
+		op->flags |= AFS_OPERATION_LOCK_1;
+	}
+
+	_leave(" = t [2]");
+	return true;
+}
+
+static void afs_drop_io_locks(struct afs_operation *op)
+{
+	struct afs_vnode *vnode = op->file[0].vnode;
+	struct afs_vnode *vnode2 = op->file[1].vnode;
+
+	_enter("");
+
+	if (op->flags & AFS_OPERATION_LOCK_1)
+		afs_unlock_for_io(vnode2);
+	if (op->flags & AFS_OPERATION_LOCK_0)
+		afs_unlock_for_io(vnode);
+}
+
+static void afs_prepare_vnode(struct afs_operation *op, struct afs_vnode_param *vp,
+			      unsigned int index)
+{
+	struct afs_vnode *vnode = vp->vnode;
+
+	if (vnode) {
+		vp->fid			= vnode->fid;
+		vp->dv_before		= vnode->status.data_version;
+		vp->cb_break_before	= afs_calc_vnode_cb_break(vnode);
+		if (vnode->lock_state != AFS_VNODE_LOCK_NONE)
+			op->flags	|= AFS_OPERATION_CUR_ONLY;
+		if (vp->modification)
+			set_bit(AFS_VNODE_MODIFYING, &vnode->flags);
+	}
+
+	if (vp->fid.vnode)
+		_debug("PREP[%u] {%llx:%llu.%u}",
+		       index, vp->fid.vid, vp->fid.vnode, vp->fid.unique);
+}
+
+/*
+ * Begin an operation on the fileserver.
+ *
+ * Fileserver operations are serialised on the server by vnode, so we serialise
+ * them here also using the io_lock.
+ */
+bool afs_begin_vnode_operation(struct afs_operation *op)
+{
+	struct afs_vnode *vnode = op->file[0].vnode;
+
+	ASSERT(vnode);
+
+	_enter("");
+
+	if (op->file[0].need_io_lock)
+		if (!afs_get_io_locks(op))
+			return false;
+
+	afs_prepare_vnode(op, &op->file[0], 0);
+	afs_prepare_vnode(op, &op->file[1], 1);
+	op->cb_v_break = atomic_read(&op->volume->cb_v_break);
+	_leave(" = true");
+	return true;
+}
+
+/*
+ * Tidy up a filesystem cursor and unlock the vnode.
+ */
+void afs_end_vnode_operation(struct afs_operation *op)
+{
+	_enter("");
+
+	switch (afs_op_error(op)) {
+	case -EDESTADDRREQ:
+	case -EADDRNOTAVAIL:
+	case -ENETUNREACH:
+	case -EHOSTUNREACH:
+		afs_dump_edestaddrreq(op);
+		break;
+	}
+
+	afs_drop_io_locks(op);
+}
+
+/*
+ * Wait for an in-progress operation to complete.
+ */
+void afs_wait_for_operation(struct afs_operation *op)
+{
+	_enter("");
+
+	while (afs_select_fileserver(op)) {
+		op->call_responded = false;
+		op->call_error = 0;
+		op->call_abort_code = 0;
+		if (test_bit(AFS_SERVER_FL_IS_YFS, &op->server->flags) &&
+		    op->ops->issue_yfs_rpc)
+			op->ops->issue_yfs_rpc(op);
+		else if (op->ops->issue_afs_rpc)
+			op->ops->issue_afs_rpc(op);
+		else
+			op->call_error = -ENOTSUPP;
+
+		if (op->call) {
+			afs_wait_for_call_to_complete(op->call);
+			op->call_abort_code = op->call->abort_code;
+			op->call_error = op->call->error;
+			op->call_responded = op->call->responded;
+			afs_put_call(op->call);
+		}
+	}
+
+	if (op->call_responded && op->server)
+		set_bit(AFS_SERVER_FL_RESPONDING, &op->server->flags);
+
+	if (!afs_op_error(op)) {
+		_debug("success");
+		op->ops->success(op);
+	} else if (op->cumul_error.aborted) {
+		if (op->ops->aborted)
+			op->ops->aborted(op);
+	} else {
+		if (op->ops->failed)
+			op->ops->failed(op);
+	}
+
+	afs_end_vnode_operation(op);
+
+	if (!afs_op_error(op) && op->ops->edit_dir) {
+		_debug("edit_dir");
+		op->ops->edit_dir(op);
+	}
+	_leave("");
+}
+
+/*
+ * Dispose of an operation.
+ */
+int afs_put_operation(struct afs_operation *op)
+{
+	struct afs_addr_list *alist;
+	int i, ret = afs_op_error(op);
+
+	_enter("op=%08x,%d", op->debug_id, ret);
+
+	if (op->ops && op->ops->put)
+		op->ops->put(op);
+	if (op->file[0].modification)
+		clear_bit(AFS_VNODE_MODIFYING, &op->file[0].vnode->flags);
+	if (op->file[1].modification && op->file[1].vnode != op->file[0].vnode)
+		clear_bit(AFS_VNODE_MODIFYING, &op->file[1].vnode->flags);
+	if (op->file[0].put_vnode)
+		iput(&op->file[0].vnode->netfs.inode);
+	if (op->file[1].put_vnode)
+		iput(&op->file[1].vnode->netfs.inode);
+
+	if (op->more_files) {
+		for (i = 0; i < op->nr_files - 2; i++)
+			if (op->more_files[i].put_vnode)
+				iput(&op->more_files[i].vnode->netfs.inode);
+		kvfree(op->more_files);
+	}
+
+	if (op->estate) {
+		alist = op->estate->addresses;
+		if (alist) {
+			if (op->call_responded &&
+			    op->addr_index != alist->preferred &&
+			    test_bit(alist->preferred, &op->addr_tried))
+				WRITE_ONCE(alist->preferred, op->addr_index);
+		}
+	}
+
+	afs_clear_server_states(op);
+	afs_put_serverlist(op->net, op->server_list);
+	afs_put_volume(op->volume, afs_volume_trace_put_put_op);
+	key_put(op->key);
+	kfree(op);
+	return ret;
+}
+
+int afs_do_sync_operation(struct afs_operation *op)
+{
+	afs_begin_vnode_operation(op);
+	afs_wait_for_operation(op);
+	return afs_put_operation(op);
+}