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, 490 insertions, 0 deletions

diff --git a/fs/afs/validation.c b/fs/afs/validation.c
new file mode 100644
index 000000000..e997563af
--- /dev/null
+++ b/fs/afs/validation.c
@@ -0,0 +1,490 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* vnode and volume validity verification.
+ *
+ * Copyright (C) 2023 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include "internal.h"
+
+/*
+ * Data validation is managed through a number of mechanisms from the server:
+ *
+ *  (1) On first contact with a server (such as if it has just been rebooted),
+ *      the server sends us a CB.InitCallBackState* request.
+ *
+ *  (2) On a RW volume, in response to certain vnode (inode)-accessing RPC
+ *      calls, the server maintains a time-limited per-vnode promise that it
+ *      will send us a CB.CallBack request if a third party alters the vnodes
+ *      accessed.
+ *
+ *      Note that a vnode-level callbacks may also be sent for other reasons,
+ *      such as filelock release.
+ *
+ *  (3) On a RO (or Backup) volume, in response to certain vnode-accessing RPC
+ *      calls, each server maintains a time-limited per-volume promise that it
+ *      will send us a CB.CallBack request if the RO volume is updated to a
+ *      snapshot of the RW volume ("vos release").  This is an atomic event
+ *      that cuts over all instances of the RO volume across multiple servers
+ *      simultaneously.
+ *
+ *	Note that a volume-level callbacks may also be sent for other reasons,
+ *	such as the volumeserver taking over control of the volume from the
+ *	fileserver.
+ *
+ *	Note also that each server maintains an independent time limit on an
+ *	independent callback.
+ *
+ *  (4) Certain RPC calls include a volume information record "VolSync" in
+ *      their reply.  This contains a creation date for the volume that should
+ *      remain unchanged for a RW volume (but will be changed if the volume is
+ *      restored from backup) or will be bumped to the time of snapshotting
+ *      when a RO volume is released.
+ *
+ * In order to track this events, the following are provided:
+ *
+ *	->cb_v_break.  A counter of events that might mean that the contents of
+ *	a volume have been altered since we last checked a vnode.
+ *
+ *	->cb_v_check.  A counter of the number of events that we've sent a
+ *	query to the server for.  Everything's up to date if this equals
+ *	cb_v_break.
+ *
+ *	->cb_scrub.  A counter of the number of regression events for which we
+ *	have to completely wipe the cache.
+ *
+ *	->cb_ro_snapshot.  A counter of the number of times that we've
+ *      recognised that a RO volume has been updated.
+ *
+ *	->cb_break.  A counter of events that might mean that the contents of a
+ *      vnode have been altered.
+ *
+ *	->cb_expires_at.  The time at which the callback promise expires or
+ *      AFS_NO_CB_PROMISE if we have no promise.
+ *
+ * The way we manage things is:
+ *
+ *  (1) When a volume-level CB.CallBack occurs, we increment ->cb_v_break on
+ *      the volume and reset ->cb_expires_at (ie. set AFS_NO_CB_PROMISE) on the
+ *      volume and volume's server record.
+ *
+ *  (2) When a CB.InitCallBackState occurs, we treat this as a volume-level
+ *	callback break on all the volumes that have been using that volume
+ *	(ie. increment ->cb_v_break and reset ->cb_expires_at).
+ *
+ *  (3) When a vnode-level CB.CallBack occurs, we increment ->cb_break on the
+ *	vnode and reset its ->cb_expires_at.  If the vnode is mmapped, we also
+ *	dispatch a work item to unmap all PTEs to the vnode's pagecache to
+ *	force reentry to the filesystem for revalidation.
+ *
+ *  (4) When entering the filesystem, we call afs_validate() to check the
+ *	validity of a vnode.  This first checks to see if ->cb_v_check and
+ *	->cb_v_break match, and if they don't, we lock volume->cb_check_lock
+ *	exclusively and perform an FS.FetchStatus on the vnode.
+ *
+ *	After checking the volume, we check the vnode.  If there's a mismatch
+ *	between the volume counters and the vnode's mirrors of those counters,
+ *	we lock vnode->validate_lock and issue an FS.FetchStatus on the vnode.
+ *
+ *  (5) When the reply from FS.FetchStatus arrives, the VolSync record is
+ *      parsed:
+ *
+ *	(A) If the Creation timestamp has changed on a RW volume or regressed
+ *	    on a RO volume, we try to increment ->cb_scrub; if it advances on a
+ *	    RO volume, we assume "vos release" happened and try to increment
+ *	    ->cb_ro_snapshot.
+ *
+ *      (B) If the Update timestamp has regressed, we try to increment
+ *	    ->cb_scrub.
+ *
+ *      Note that in both of these cases, we only do the increment if we can
+ *      cmpxchg the value of the timestamp from the value we noted before the
+ *      op.  This tries to prevent parallel ops from fighting one another.
+ *
+ *	volume->cb_v_check is then set to ->cb_v_break.
+ *
+ *  (6) The AFSCallBack record included in the FS.FetchStatus reply is also
+ *	parsed and used to set the promise in ->cb_expires_at for the vnode,
+ *	the volume and the volume's server record.
+ *
+ *  (7) If ->cb_scrub is seen to have advanced, we invalidate the pagecache for
+ *      the vnode.
+ */
+
+/*
+ * Check the validity of a vnode/inode and its parent volume.
+ */
+bool afs_check_validity(const struct afs_vnode *vnode)
+{
+	const struct afs_volume *volume = vnode->volume;
+	enum afs_vnode_invalid_trace trace = afs_vnode_valid_trace;
+	time64_t cb_expires_at = atomic64_read(&vnode->cb_expires_at);
+	time64_t deadline = ktime_get_real_seconds() + 10;
+
+	if (test_bit(AFS_VNODE_DELETED, &vnode->flags))
+		return true;
+
+	if (atomic_read(&volume->cb_v_check) != atomic_read(&volume->cb_v_break))
+		trace = afs_vnode_invalid_trace_cb_v_break;
+	else if (cb_expires_at == AFS_NO_CB_PROMISE)
+		trace = afs_vnode_invalid_trace_no_cb_promise;
+	else if (cb_expires_at <= deadline)
+		trace = afs_vnode_invalid_trace_expired;
+	else if (volume->cb_expires_at <= deadline)
+		trace = afs_vnode_invalid_trace_vol_expired;
+	else if (vnode->cb_ro_snapshot != atomic_read(&volume->cb_ro_snapshot))
+		trace = afs_vnode_invalid_trace_cb_ro_snapshot;
+	else if (vnode->cb_scrub != atomic_read(&volume->cb_scrub))
+		trace = afs_vnode_invalid_trace_cb_scrub;
+	else if (test_bit(AFS_VNODE_ZAP_DATA, &vnode->flags))
+		trace = afs_vnode_invalid_trace_zap_data;
+	else
+		return true;
+	trace_afs_vnode_invalid(vnode, trace);
+	return false;
+}
+
+/*
+ * See if the server we've just talked to is currently excluded.
+ */
+static bool __afs_is_server_excluded(struct afs_operation *op, struct afs_volume *volume)
+{
+	const struct afs_server_entry *se;
+	const struct afs_server_list *slist;
+	bool is_excluded = true;
+	int i;
+
+	rcu_read_lock();
+
+	slist = rcu_dereference(volume->servers);
+	for (i = 0; i < slist->nr_servers; i++) {
+		se = &slist->servers[i];
+		if (op->server == se->server) {
+			is_excluded = test_bit(AFS_SE_EXCLUDED, &se->flags);
+			break;
+		}
+	}
+
+	rcu_read_unlock();
+	return is_excluded;
+}
+
+/*
+ * Update the volume's server list when the creation time changes and see if
+ * the server we've just talked to is currently excluded.
+ */
+static int afs_is_server_excluded(struct afs_operation *op, struct afs_volume *volume)
+{
+	int ret;
+
+	if (__afs_is_server_excluded(op, volume))
+		return 1;
+
+	set_bit(AFS_VOLUME_NEEDS_UPDATE, &volume->flags);
+	ret = afs_check_volume_status(op->volume, op);
+	if (ret < 0)
+		return ret;
+
+	return __afs_is_server_excluded(op, volume);
+}
+
+/*
+ * Handle a change to the volume creation time in the VolSync record.
+ */
+static int afs_update_volume_creation_time(struct afs_operation *op, struct afs_volume *volume)
+{
+	unsigned int snap;
+	time64_t cur = volume->creation_time;
+	time64_t old = op->pre_volsync.creation;
+	time64_t new = op->volsync.creation;
+	int ret;
+
+	_enter("%llx,%llx,%llx->%llx", volume->vid, cur, old, new);
+
+	if (cur == TIME64_MIN) {
+		volume->creation_time = new;
+		return 0;
+	}
+
+	if (new == cur)
+		return 0;
+
+	/* Try to advance the creation timestamp from what we had before the
+	 * operation to what we got back from the server.  This should
+	 * hopefully ensure that in a race between multiple operations only one
+	 * of them will do this.
+	 */
+	if (cur != old)
+		return 0;
+
+	/* If the creation time changes in an unexpected way, we need to scrub
+	 * our caches.  For a RW vol, this will only change if the volume is
+	 * restored from a backup; for a RO/Backup vol, this will advance when
+	 * the volume is updated to a new snapshot (eg. "vos release").
+	 */
+	if (volume->type == AFSVL_RWVOL)
+		goto regressed;
+	if (volume->type == AFSVL_BACKVOL) {
+		if (new < old)
+			goto regressed;
+		goto advance;
+	}
+
+	/* We have an RO volume, we need to query the VL server and look at the
+	 * server flags to see if RW->RO replication is in progress.
+	 */
+	ret = afs_is_server_excluded(op, volume);
+	if (ret < 0)
+		return ret;
+	if (ret > 0) {
+		snap = atomic_read(&volume->cb_ro_snapshot);
+		trace_afs_cb_v_break(volume->vid, snap, afs_cb_break_volume_excluded);
+		return ret;
+	}
+
+advance:
+	snap = atomic_inc_return(&volume->cb_ro_snapshot);
+	trace_afs_cb_v_break(volume->vid, snap, afs_cb_break_for_vos_release);
+	volume->creation_time = new;
+	return 0;
+
+regressed:
+	atomic_inc(&volume->cb_scrub);
+	trace_afs_cb_v_break(volume->vid, 0, afs_cb_break_for_creation_regress);
+	volume->creation_time = new;
+	return 0;
+}
+
+/*
+ * Handle a change to the volume update time in the VolSync record.
+ */
+static void afs_update_volume_update_time(struct afs_operation *op, struct afs_volume *volume)
+{
+	enum afs_cb_break_reason reason = afs_cb_break_no_break;
+	time64_t cur = volume->update_time;
+	time64_t old = op->pre_volsync.update;
+	time64_t new = op->volsync.update;
+
+	_enter("%llx,%llx,%llx->%llx", volume->vid, cur, old, new);
+
+	if (cur == TIME64_MIN) {
+		volume->update_time = new;
+		return;
+	}
+
+	if (new == cur)
+		return;
+
+	/* If the volume update time changes in an unexpected way, we need to
+	 * scrub our caches.  For a RW vol, this will advance on every
+	 * modification op; for a RO/Backup vol, this will advance when the
+	 * volume is updated to a new snapshot (eg. "vos release").
+	 */
+	if (new < old)
+		reason = afs_cb_break_for_update_regress;
+
+	/* Try to advance the update timestamp from what we had before the
+	 * operation to what we got back from the server.  This should
+	 * hopefully ensure that in a race between multiple operations only one
+	 * of them will do this.
+	 */
+	if (cur == old) {
+		if (reason == afs_cb_break_for_update_regress) {
+			atomic_inc(&volume->cb_scrub);
+			trace_afs_cb_v_break(volume->vid, 0, reason);
+		}
+		volume->update_time = new;
+	}
+}
+
+static int afs_update_volume_times(struct afs_operation *op, struct afs_volume *volume)
+{
+	int ret = 0;
+
+	if (likely(op->volsync.creation == volume->creation_time &&
+		   op->volsync.update == volume->update_time))
+		return 0;
+
+	mutex_lock(&volume->volsync_lock);
+	if (op->volsync.creation != volume->creation_time) {
+		ret = afs_update_volume_creation_time(op, volume);
+		if (ret < 0)
+			goto out;
+	}
+	if (op->volsync.update != volume->update_time)
+		afs_update_volume_update_time(op, volume);
+out:
+	mutex_unlock(&volume->volsync_lock);
+	return ret;
+}
+
+/*
+ * Update the state of a volume, including recording the expiration time of the
+ * callback promise.  Returns 1 to redo the operation from the start.
+ */
+int afs_update_volume_state(struct afs_operation *op)
+{
+	struct afs_server_list *slist = op->server_list;
+	struct afs_server_entry *se = &slist->servers[op->server_index];
+	struct afs_callback *cb = &op->file[0].scb.callback;
+	struct afs_volume *volume = op->volume;
+	unsigned int cb_v_break = atomic_read(&volume->cb_v_break);
+	unsigned int cb_v_check = atomic_read(&volume->cb_v_check);
+	int ret;
+
+	_enter("%llx", op->volume->vid);
+
+	if (op->volsync.creation != TIME64_MIN || op->volsync.update != TIME64_MIN) {
+		ret = afs_update_volume_times(op, volume);
+		if (ret != 0) {
+			_leave(" = %d", ret);
+			return ret;
+		}
+	}
+
+	if (op->cb_v_break == cb_v_break &&
+	    (op->file[0].scb.have_cb || op->file[1].scb.have_cb)) {
+		time64_t expires_at = cb->expires_at;
+
+		if (!op->file[0].scb.have_cb)
+			expires_at = op->file[1].scb.callback.expires_at;
+
+		se->cb_expires_at = expires_at;
+		volume->cb_expires_at = expires_at;
+	}
+	if (cb_v_check < op->cb_v_break)
+		atomic_cmpxchg(&volume->cb_v_check, cb_v_check, op->cb_v_break);
+	return 0;
+}
+
+/*
+ * mark the data attached to an inode as obsolete due to a write on the server
+ * - might also want to ditch all the outstanding writes and dirty pages
+ */
+static void afs_zap_data(struct afs_vnode *vnode)
+{
+	_enter("{%llx:%llu}", vnode->fid.vid, vnode->fid.vnode);
+
+	afs_invalidate_cache(vnode, 0);
+
+	/* nuke all the non-dirty pages that aren't locked, mapped or being
+	 * written back in a regular file and completely discard the pages in a
+	 * directory or symlink */
+	if (S_ISREG(vnode->netfs.inode.i_mode))
+		filemap_invalidate_inode(&vnode->netfs.inode, true, 0, LLONG_MAX);
+	else
+		filemap_invalidate_inode(&vnode->netfs.inode, false, 0, LLONG_MAX);
+}
+
+/*
+ * validate a vnode/inode
+ * - there are several things we need to check
+ *   - parent dir data changes (rm, rmdir, rename, mkdir, create, link,
+ *     symlink)
+ *   - parent dir metadata changed (security changes)
+ *   - dentry data changed (write, truncate)
+ *   - dentry metadata changed (security changes)
+ */
+int afs_validate(struct afs_vnode *vnode, struct key *key)
+{
+	struct afs_volume *volume = vnode->volume;
+	unsigned int cb_ro_snapshot, cb_scrub;
+	time64_t deadline = ktime_get_real_seconds() + 10;
+	bool zap = false, locked_vol = false;
+	int ret;
+
+	_enter("{v={%llx:%llu} fl=%lx},%x",
+	       vnode->fid.vid, vnode->fid.vnode, vnode->flags,
+	       key_serial(key));
+
+	if (afs_check_validity(vnode))
+		return test_bit(AFS_VNODE_DELETED, &vnode->flags) ? -ESTALE : 0;
+
+	ret = down_write_killable(&vnode->validate_lock);
+	if (ret < 0)
+		goto error;
+
+	if (test_bit(AFS_VNODE_DELETED, &vnode->flags)) {
+		ret = -ESTALE;
+		goto error_unlock;
+	}
+
+	/* Validate a volume after the v_break has changed or the volume
+	 * callback expired.  We only want to do this once per volume per
+	 * v_break change.  The actual work will be done when parsing the
+	 * status fetch reply.
+	 */
+	if (volume->cb_expires_at <= deadline ||
+	    atomic_read(&volume->cb_v_check) != atomic_read(&volume->cb_v_break)) {
+		ret = mutex_lock_interruptible(&volume->cb_check_lock);
+		if (ret < 0)
+			goto error_unlock;
+		locked_vol = true;
+	}
+
+	cb_ro_snapshot = atomic_read(&volume->cb_ro_snapshot);
+	cb_scrub = atomic_read(&volume->cb_scrub);
+	if (vnode->cb_ro_snapshot != cb_ro_snapshot ||
+	    vnode->cb_scrub	  != cb_scrub)
+		unmap_mapping_pages(vnode->netfs.inode.i_mapping, 0, 0, false);
+
+	if (vnode->cb_ro_snapshot != cb_ro_snapshot ||
+	    vnode->cb_scrub	  != cb_scrub ||
+	    volume->cb_expires_at <= deadline ||
+	    atomic_read(&volume->cb_v_check) != atomic_read(&volume->cb_v_break) ||
+	    atomic64_read(&vnode->cb_expires_at) <= deadline
+	    ) {
+		ret = afs_fetch_status(vnode, key, false, NULL);
+		if (ret < 0) {
+			if (ret == -ENOENT) {
+				set_bit(AFS_VNODE_DELETED, &vnode->flags);
+				ret = -ESTALE;
+			}
+			goto error_unlock;
+		}
+
+		_debug("new promise [fl=%lx]", vnode->flags);
+	}
+
+	/* We can drop the volume lock now as. */
+	if (locked_vol) {
+		mutex_unlock(&volume->cb_check_lock);
+		locked_vol = false;
+	}
+
+	cb_ro_snapshot = atomic_read(&volume->cb_ro_snapshot);
+	cb_scrub = atomic_read(&volume->cb_scrub);
+	_debug("vnode inval %x==%x %x==%x",
+	       vnode->cb_ro_snapshot, cb_ro_snapshot,
+	       vnode->cb_scrub, cb_scrub);
+	if (vnode->cb_scrub != cb_scrub)
+		zap = true;
+	vnode->cb_ro_snapshot = cb_ro_snapshot;
+	vnode->cb_scrub = cb_scrub;
+
+	/* If the vnode's data version number changed then its contents are
+	 * different.  Note that afs_apply_status() doesn't set ZAP_DATA on
+	 * directories.
+	 */
+	zap |= test_and_clear_bit(AFS_VNODE_ZAP_DATA, &vnode->flags);
+	if (zap) {
+		if (S_ISREG(vnode->netfs.inode.i_mode))
+			afs_zap_data(vnode);
+		else if (S_ISLNK(vnode->netfs.inode.i_mode))
+			afs_invalidate_symlink(vnode);
+	}
+	up_write(&vnode->validate_lock);
+	_leave(" = 0");
+	return 0;
+
+error_unlock:
+	if (locked_vol)
+		mutex_unlock(&volume->cb_check_lock);
+	up_write(&vnode->validate_lock);
+error:
+	_leave(" = %d", ret);
+	return ret;
+}