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, 520 insertions, 0 deletions

diff --git a/fs/afs/security.c b/fs/afs/security.c
new file mode 100644
index 000000000..6d00d62a6
--- /dev/null
+++ b/fs/afs/security.c
@@ -0,0 +1,520 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* AFS security handling
+ *
+ * Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/ctype.h>
+#include <linux/sched.h>
+#include <linux/hashtable.h>
+#include <keys/rxrpc-type.h>
+#include "internal.h"
+
+static DEFINE_HASHTABLE(afs_permits_cache, 10);
+static DEFINE_SPINLOCK(afs_permits_lock);
+static DEFINE_MUTEX(afs_key_lock);
+
+/*
+ * Allocate a key to use as a placeholder for anonymous user security.
+ */
+static int afs_alloc_anon_key(struct afs_cell *cell)
+{
+	struct key *key;
+
+	mutex_lock(&afs_key_lock);
+	key = cell->anonymous_key;
+	if (!key) {
+		key = rxrpc_get_null_key(cell->key_desc);
+		if (!IS_ERR(key))
+			cell->anonymous_key = key;
+	}
+	mutex_unlock(&afs_key_lock);
+
+	if (IS_ERR(key))
+		return PTR_ERR(key);
+
+	_debug("anon key %p{%x}",
+	       cell->anonymous_key, key_serial(cell->anonymous_key));
+	return 0;
+}
+
+/*
+ * get a key
+ */
+struct key *afs_request_key(struct afs_cell *cell)
+{
+	struct key *key;
+	int ret;
+
+	_enter("{%s}", cell->key_desc);
+
+	_debug("key %s", cell->key_desc);
+	key = request_key_net(&key_type_rxrpc, cell->key_desc,
+			      cell->net->net, NULL);
+	if (IS_ERR(key)) {
+		if (PTR_ERR(key) != -ENOKEY) {
+			_leave(" = %ld", PTR_ERR(key));
+			return key;
+		}
+
+		if (!cell->anonymous_key) {
+			ret = afs_alloc_anon_key(cell);
+			if (ret < 0)
+				return ERR_PTR(ret);
+		}
+
+		/* act as anonymous user */
+		_leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
+		return key_get(cell->anonymous_key);
+	} else {
+		/* act as authorised user */
+		_leave(" = {%x} [auth]", key_serial(key));
+		return key;
+	}
+}
+
+/*
+ * Get a key when pathwalk is in rcuwalk mode.
+ */
+struct key *afs_request_key_rcu(struct afs_cell *cell)
+{
+	struct key *key;
+
+	_enter("{%s}", cell->key_desc);
+
+	_debug("key %s", cell->key_desc);
+	key = request_key_net_rcu(&key_type_rxrpc, cell->key_desc,
+				  cell->net->net);
+	if (IS_ERR(key)) {
+		if (PTR_ERR(key) != -ENOKEY) {
+			_leave(" = %ld", PTR_ERR(key));
+			return key;
+		}
+
+		/* act as anonymous user */
+		if (!cell->anonymous_key)
+			return NULL; /* Need to allocate */
+		_leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
+		return key_get(cell->anonymous_key);
+	} else {
+		/* act as authorised user */
+		_leave(" = {%x} [auth]", key_serial(key));
+		return key;
+	}
+}
+
+/*
+ * Dispose of a list of permits.
+ */
+static void afs_permits_rcu(struct rcu_head *rcu)
+{
+	struct afs_permits *permits =
+		container_of(rcu, struct afs_permits, rcu);
+	int i;
+
+	for (i = 0; i < permits->nr_permits; i++)
+		key_put(permits->permits[i].key);
+	kfree(permits);
+}
+
+/*
+ * Discard a permission cache.
+ */
+void afs_put_permits(struct afs_permits *permits)
+{
+	if (permits && refcount_dec_and_test(&permits->usage)) {
+		spin_lock(&afs_permits_lock);
+		hash_del_rcu(&permits->hash_node);
+		spin_unlock(&afs_permits_lock);
+		call_rcu(&permits->rcu, afs_permits_rcu);
+	}
+}
+
+/*
+ * Clear a permit cache on callback break.
+ */
+void afs_clear_permits(struct afs_vnode *vnode)
+{
+	struct afs_permits *permits;
+
+	spin_lock(&vnode->lock);
+	permits = rcu_dereference_protected(vnode->permit_cache,
+					    lockdep_is_held(&vnode->lock));
+	RCU_INIT_POINTER(vnode->permit_cache, NULL);
+	spin_unlock(&vnode->lock);
+
+	afs_put_permits(permits);
+}
+
+/*
+ * Hash a list of permits.  Use simple addition to make it easy to add an extra
+ * one at an as-yet indeterminate position in the list.
+ */
+static void afs_hash_permits(struct afs_permits *permits)
+{
+	unsigned long h = permits->nr_permits;
+	int i;
+
+	for (i = 0; i < permits->nr_permits; i++) {
+		h += (unsigned long)permits->permits[i].key / sizeof(void *);
+		h += permits->permits[i].access;
+	}
+
+	permits->h = h;
+}
+
+/*
+ * Cache the CallerAccess result obtained from doing a fileserver operation
+ * that returned a vnode status for a particular key.  If a callback break
+ * occurs whilst the operation was in progress then we have to ditch the cache
+ * as the ACL *may* have changed.
+ */
+void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
+		      unsigned int cb_break, struct afs_status_cb *scb)
+{
+	struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
+	afs_access_t caller_access = scb->status.caller_access;
+	size_t size = 0;
+	bool changed = false;
+	int i, j;
+
+	_enter("{%llx:%llu},%x,%x",
+	       vnode->fid.vid, vnode->fid.vnode, key_serial(key), caller_access);
+
+	rcu_read_lock();
+
+	/* Check for the common case first: We got back the same access as last
+	 * time we tried and already have it recorded.
+	 */
+	permits = rcu_dereference(vnode->permit_cache);
+	if (permits) {
+		if (!permits->invalidated) {
+			for (i = 0; i < permits->nr_permits; i++) {
+				if (permits->permits[i].key < key)
+					continue;
+				if (permits->permits[i].key > key)
+					break;
+				if (permits->permits[i].access != caller_access) {
+					changed = true;
+					break;
+				}
+
+				if (afs_cb_is_broken(cb_break, vnode)) {
+					changed = true;
+					break;
+				}
+
+				/* The cache is still good. */
+				rcu_read_unlock();
+				return;
+			}
+		}
+
+		changed |= permits->invalidated;
+		size = permits->nr_permits;
+
+		/* If this set of permits is now wrong, clear the permits
+		 * pointer so that no one tries to use the stale information.
+		 */
+		if (changed) {
+			spin_lock(&vnode->lock);
+			if (permits != rcu_access_pointer(vnode->permit_cache))
+				goto someone_else_changed_it_unlock;
+			RCU_INIT_POINTER(vnode->permit_cache, NULL);
+			spin_unlock(&vnode->lock);
+
+			afs_put_permits(permits);
+			permits = NULL;
+			size = 0;
+		}
+	}
+
+	if (afs_cb_is_broken(cb_break, vnode))
+		goto someone_else_changed_it;
+
+	/* We need a ref on any permits list we want to copy as we'll have to
+	 * drop the lock to do memory allocation.
+	 */
+	if (permits && !refcount_inc_not_zero(&permits->usage))
+		goto someone_else_changed_it;
+
+	rcu_read_unlock();
+
+	/* Speculatively create a new list with the revised permission set.  We
+	 * discard this if we find an extant match already in the hash, but
+	 * it's easier to compare with memcmp this way.
+	 *
+	 * We fill in the key pointers at this time, but we don't get the refs
+	 * yet.
+	 */
+	size++;
+	new = kzalloc_flex(*new, permits, size, GFP_NOFS);
+	if (!new)
+		goto out_put;
+
+	refcount_set(&new->usage, 1);
+	new->nr_permits = size;
+	i = j = 0;
+	if (permits) {
+		for (i = 0; i < permits->nr_permits; i++) {
+			if (j == i && permits->permits[i].key > key) {
+				new->permits[j].key = key;
+				new->permits[j].access = caller_access;
+				j++;
+			}
+			new->permits[j].key = permits->permits[i].key;
+			new->permits[j].access = permits->permits[i].access;
+			j++;
+		}
+	}
+
+	if (j == i) {
+		new->permits[j].key = key;
+		new->permits[j].access = caller_access;
+	}
+
+	afs_hash_permits(new);
+
+	/* Now see if the permit list we want is actually already available */
+	spin_lock(&afs_permits_lock);
+
+	hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
+		if (xpermits->h != new->h ||
+		    xpermits->invalidated ||
+		    xpermits->nr_permits != new->nr_permits ||
+		    memcmp(xpermits->permits, new->permits,
+			   new->nr_permits * sizeof(struct afs_permit)) != 0)
+			continue;
+
+		if (refcount_inc_not_zero(&xpermits->usage)) {
+			replacement = xpermits;
+			goto found;
+		}
+
+		break;
+	}
+
+	for (i = 0; i < new->nr_permits; i++)
+		key_get(new->permits[i].key);
+	hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
+	replacement = new;
+	new = NULL;
+
+found:
+	spin_unlock(&afs_permits_lock);
+
+	kfree(new);
+
+	rcu_read_lock();
+	spin_lock(&vnode->lock);
+	zap = rcu_access_pointer(vnode->permit_cache);
+	if (!afs_cb_is_broken(cb_break, vnode) && zap == permits)
+		rcu_assign_pointer(vnode->permit_cache, replacement);
+	else
+		zap = replacement;
+	spin_unlock(&vnode->lock);
+	rcu_read_unlock();
+	afs_put_permits(zap);
+out_put:
+	afs_put_permits(permits);
+	return;
+
+someone_else_changed_it_unlock:
+	spin_unlock(&vnode->lock);
+someone_else_changed_it:
+	/* Someone else changed the cache under us - don't recheck at this
+	 * time.
+	 */
+	rcu_read_unlock();
+	return;
+}
+
+static bool afs_check_permit_rcu(struct afs_vnode *vnode, struct key *key,
+				 afs_access_t *_access)
+{
+	const struct afs_permits *permits;
+	int i;
+
+	_enter("{%llx:%llu},%x",
+	       vnode->fid.vid, vnode->fid.vnode, key_serial(key));
+
+	/* check the permits to see if we've got one yet */
+	if (key == vnode->volume->cell->anonymous_key) {
+		*_access = vnode->status.anon_access;
+		_leave(" = t [anon %x]", *_access);
+		return true;
+	}
+
+	permits = rcu_dereference(vnode->permit_cache);
+	if (permits) {
+		for (i = 0; i < permits->nr_permits; i++) {
+			if (permits->permits[i].key < key)
+				continue;
+			if (permits->permits[i].key > key)
+				break;
+
+			*_access = permits->permits[i].access;
+			_leave(" = %u [perm %x]", !permits->invalidated, *_access);
+			return !permits->invalidated;
+		}
+	}
+
+	_leave(" = f");
+	return false;
+}
+
+/*
+ * check with the fileserver to see if the directory or parent directory is
+ * permitted to be accessed with this authorisation, and if so, what access it
+ * is granted
+ */
+int afs_check_permit(struct afs_vnode *vnode, struct key *key,
+		     afs_access_t *_access)
+{
+	struct afs_permits *permits;
+	bool valid = false;
+	int i, ret;
+
+	_enter("{%llx:%llu},%x",
+	       vnode->fid.vid, vnode->fid.vnode, key_serial(key));
+
+	/* check the permits to see if we've got one yet */
+	if (key == vnode->volume->cell->anonymous_key) {
+		_debug("anon");
+		*_access = vnode->status.anon_access;
+		valid = true;
+	} else {
+		rcu_read_lock();
+		permits = rcu_dereference(vnode->permit_cache);
+		if (permits) {
+			for (i = 0; i < permits->nr_permits; i++) {
+				if (permits->permits[i].key < key)
+					continue;
+				if (permits->permits[i].key > key)
+					break;
+
+				*_access = permits->permits[i].access;
+				valid = !permits->invalidated;
+				break;
+			}
+		}
+		rcu_read_unlock();
+	}
+
+	if (!valid) {
+		/* Check the status on the file we're actually interested in
+		 * (the post-processing will cache the result).
+		 */
+		_debug("no valid permit");
+
+		ret = afs_fetch_status(vnode, key, false, _access);
+		if (ret < 0) {
+			*_access = 0;
+			_leave(" = %d", ret);
+			return ret;
+		}
+	}
+
+	_leave(" = 0 [access %x]", *_access);
+	return 0;
+}
+
+/*
+ * check the permissions on an AFS file
+ * - AFS ACLs are attached to directories only, and a file is controlled by its
+ *   parent directory's ACL
+ */
+int afs_permission(struct mnt_idmap *idmap, struct inode *inode,
+		   int mask)
+{
+	struct afs_vnode *vnode = AFS_FS_I(inode);
+	afs_access_t access;
+	struct key *key;
+	int ret = 0;
+
+	_enter("{{%llx:%llu},%lx},%x,",
+	       vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
+
+	if (mask & MAY_NOT_BLOCK) {
+		key = afs_request_key_rcu(vnode->volume->cell);
+		if (IS_ERR_OR_NULL(key))
+			return -ECHILD;
+
+		ret = -ECHILD;
+		if (!afs_check_validity(vnode) ||
+		    !afs_check_permit_rcu(vnode, key, &access))
+			goto error;
+	} else {
+		key = afs_request_key(vnode->volume->cell);
+		if (IS_ERR(key)) {
+			_leave(" = %ld [key]", PTR_ERR(key));
+			return PTR_ERR(key);
+		}
+
+		ret = afs_validate(vnode, key);
+		if (ret < 0)
+			goto error;
+
+		/* check the permits to see if we've got one yet */
+		ret = afs_check_permit(vnode, key, &access);
+		if (ret < 0)
+			goto error;
+	}
+
+	/* interpret the access mask */
+	_debug("REQ %x ACC %x on %s",
+	       mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
+
+	ret = 0;
+	if (S_ISDIR(inode->i_mode)) {
+		if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
+			if (!(access & AFS_ACE_LOOKUP))
+				goto permission_denied;
+		}
+		if (mask & MAY_WRITE) {
+			if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
+					AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
+				goto permission_denied;
+		}
+	} else {
+		if (!(access & AFS_ACE_LOOKUP))
+			goto permission_denied;
+		if ((mask & MAY_EXEC) && !(inode->i_mode & S_IXUSR))
+			goto permission_denied;
+		if (mask & (MAY_EXEC | MAY_READ)) {
+			if (!(access & AFS_ACE_READ))
+				goto permission_denied;
+			if (!(inode->i_mode & S_IRUSR))
+				goto permission_denied;
+		} else if (mask & MAY_WRITE) {
+			if (!(access & AFS_ACE_WRITE))
+				goto permission_denied;
+			if (!(inode->i_mode & S_IWUSR))
+				goto permission_denied;
+		}
+	}
+
+	key_put(key);
+	_leave(" = %d", ret);
+	return ret;
+
+permission_denied:
+	ret = -EACCES;
+error:
+	key_put(key);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+void __exit afs_clean_up_permit_cache(void)
+{
+	int i;
+
+	for (i = 0; i < HASH_SIZE(afs_permits_cache); i++)
+		WARN_ON_ONCE(!hlist_empty(&afs_permits_cache[i]));
+
+}