From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- drivers/net/wireguard/peer.c | 239 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 239 insertions(+) create mode 100644 drivers/net/wireguard/peer.c (limited to 'drivers/net/wireguard/peer.c') diff --git a/drivers/net/wireguard/peer.c b/drivers/net/wireguard/peer.c new file mode 100644 index 000000000..1cb502a93 --- /dev/null +++ b/drivers/net/wireguard/peer.c @@ -0,0 +1,239 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2015-2019 Jason A. Donenfeld . All Rights Reserved. + */ + +#include "peer.h" +#include "device.h" +#include "queueing.h" +#include "timers.h" +#include "peerlookup.h" +#include "noise.h" + +#include +#include +#include +#include + +static struct kmem_cache *peer_cache; +static atomic64_t peer_counter = ATOMIC64_INIT(0); + +struct wg_peer *wg_peer_create(struct wg_device *wg, + const u8 public_key[NOISE_PUBLIC_KEY_LEN], + const u8 preshared_key[NOISE_SYMMETRIC_KEY_LEN]) +{ + struct wg_peer *peer; + int ret = -ENOMEM; + + lockdep_assert_held(&wg->device_update_lock); + + if (wg->num_peers >= MAX_PEERS_PER_DEVICE) + return ERR_PTR(ret); + + peer = kmem_cache_zalloc(peer_cache, GFP_KERNEL); + if (unlikely(!peer)) + return ERR_PTR(ret); + if (unlikely(dst_cache_init(&peer->endpoint_cache, GFP_KERNEL))) + goto err; + + peer->device = wg; + wg_noise_handshake_init(&peer->handshake, &wg->static_identity, + public_key, preshared_key, peer); + peer->internal_id = atomic64_inc_return(&peer_counter); + peer->serial_work_cpu = nr_cpumask_bits; + wg_cookie_init(&peer->latest_cookie); + wg_timers_init(peer); + wg_cookie_checker_precompute_peer_keys(peer); + spin_lock_init(&peer->keypairs.keypair_update_lock); + INIT_WORK(&peer->transmit_handshake_work, wg_packet_handshake_send_worker); + INIT_WORK(&peer->transmit_packet_work, wg_packet_tx_worker); + wg_prev_queue_init(&peer->tx_queue); + wg_prev_queue_init(&peer->rx_queue); + rwlock_init(&peer->endpoint_lock); + kref_init(&peer->refcount); + skb_queue_head_init(&peer->staged_packet_queue); + wg_noise_reset_last_sent_handshake(&peer->last_sent_handshake); + set_bit(NAPI_STATE_NO_BUSY_POLL, &peer->napi.state); + netif_napi_add(wg->dev, &peer->napi, wg_packet_rx_poll); + napi_enable(&peer->napi); + list_add_tail(&peer->peer_list, &wg->peer_list); + INIT_LIST_HEAD(&peer->allowedips_list); + wg_pubkey_hashtable_add(wg->peer_hashtable, peer); + ++wg->num_peers; + pr_debug("%s: Peer %llu created\n", wg->dev->name, peer->internal_id); + return peer; + +err: + kmem_cache_free(peer_cache, peer); + return ERR_PTR(ret); +} + +struct wg_peer *wg_peer_get_maybe_zero(struct wg_peer *peer) +{ + RCU_LOCKDEP_WARN(!rcu_read_lock_bh_held(), + "Taking peer reference without holding the RCU read lock"); + if (unlikely(!peer || !kref_get_unless_zero(&peer->refcount))) + return NULL; + return peer; +} + +static void peer_make_dead(struct wg_peer *peer) +{ + /* Remove from configuration-time lookup structures. */ + list_del_init(&peer->peer_list); + wg_allowedips_remove_by_peer(&peer->device->peer_allowedips, peer, + &peer->device->device_update_lock); + wg_pubkey_hashtable_remove(peer->device->peer_hashtable, peer); + + /* Mark as dead, so that we don't allow jumping contexts after. */ + WRITE_ONCE(peer->is_dead, true); + + /* The caller must now synchronize_net() for this to take effect. */ +} + +static void peer_remove_after_dead(struct wg_peer *peer) +{ + WARN_ON(!peer->is_dead); + + /* No more keypairs can be created for this peer, since is_dead protects + * add_new_keypair, so we can now destroy existing ones. + */ + wg_noise_keypairs_clear(&peer->keypairs); + + /* Destroy all ongoing timers that were in-flight at the beginning of + * this function. + */ + wg_timers_stop(peer); + + /* The transition between packet encryption/decryption queues isn't + * guarded by is_dead, but each reference's life is strictly bounded by + * two generations: once for parallel crypto and once for serial + * ingestion, so we can simply flush twice, and be sure that we no + * longer have references inside these queues. + */ + + /* a) For encrypt/decrypt. */ + flush_workqueue(peer->device->packet_crypt_wq); + /* b.1) For send (but not receive, since that's napi). */ + flush_workqueue(peer->device->packet_crypt_wq); + /* b.2.1) For receive (but not send, since that's wq). */ + napi_disable(&peer->napi); + /* b.2.1) It's now safe to remove the napi struct, which must be done + * here from process context. + */ + netif_napi_del(&peer->napi); + + /* Ensure any workstructs we own (like transmit_handshake_work or + * clear_peer_work) no longer are in use. + */ + flush_workqueue(peer->device->handshake_send_wq); + + /* After the above flushes, a peer might still be active in a few + * different contexts: 1) from xmit(), before hitting is_dead and + * returning, 2) from wg_packet_consume_data(), before hitting is_dead + * and returning, 3) from wg_receive_handshake_packet() after a point + * where it has processed an incoming handshake packet, but where + * all calls to pass it off to timers fails because of is_dead. We won't + * have new references in (1) eventually, because we're removed from + * allowedips; we won't have new references in (2) eventually, because + * wg_index_hashtable_lookup will always return NULL, since we removed + * all existing keypairs and no more can be created; we won't have new + * references in (3) eventually, because we're removed from the pubkey + * hash table, which allows for a maximum of one handshake response, + * via the still-uncleared index hashtable entry, but not more than one, + * and in wg_cookie_message_consume, the lookup eventually gets a peer + * with a refcount of zero, so no new reference is taken. + */ + + --peer->device->num_peers; + wg_peer_put(peer); +} + +/* We have a separate "remove" function make sure that all active places where + * a peer is currently operating will eventually come to an end and not pass + * their reference onto another context. + */ +void wg_peer_remove(struct wg_peer *peer) +{ + if (unlikely(!peer)) + return; + lockdep_assert_held(&peer->device->device_update_lock); + + peer_make_dead(peer); + synchronize_net(); + peer_remove_after_dead(peer); +} + +void wg_peer_remove_all(struct wg_device *wg) +{ + struct wg_peer *peer, *temp; + LIST_HEAD(dead_peers); + + lockdep_assert_held(&wg->device_update_lock); + + /* Avoid having to traverse individually for each one. */ + wg_allowedips_free(&wg->peer_allowedips, &wg->device_update_lock); + + list_for_each_entry_safe(peer, temp, &wg->peer_list, peer_list) { + peer_make_dead(peer); + list_add_tail(&peer->peer_list, &dead_peers); + } + synchronize_net(); + list_for_each_entry_safe(peer, temp, &dead_peers, peer_list) + peer_remove_after_dead(peer); +} + +static void rcu_release(struct rcu_head *rcu) +{ + struct wg_peer *peer = container_of(rcu, struct wg_peer, rcu); + + dst_cache_destroy(&peer->endpoint_cache); + WARN_ON(wg_prev_queue_peek(&peer->tx_queue) || wg_prev_queue_peek(&peer->rx_queue)); + + /* The final zeroing takes care of clearing any remaining handshake key + * material and other potentially sensitive information. + */ + memzero_explicit(peer, sizeof(*peer)); + kmem_cache_free(peer_cache, peer); +} + +static void kref_release(struct kref *refcount) +{ + struct wg_peer *peer = container_of(refcount, struct wg_peer, refcount); + + pr_debug("%s: Peer %llu (%pISpfsc) destroyed\n", + peer->device->dev->name, peer->internal_id, + &peer->endpoint.addr); + + /* Remove ourself from dynamic runtime lookup structures, now that the + * last reference is gone. + */ + wg_index_hashtable_remove(peer->device->index_hashtable, + &peer->handshake.entry); + + /* Remove any lingering packets that didn't have a chance to be + * transmitted. + */ + wg_packet_purge_staged_packets(peer); + + /* Free the memory used. */ + call_rcu(&peer->rcu, rcu_release); +} + +void wg_peer_put(struct wg_peer *peer) +{ + if (unlikely(!peer)) + return; + kref_put(&peer->refcount, kref_release); +} + +int __init wg_peer_init(void) +{ + peer_cache = KMEM_CACHE(wg_peer, 0); + return peer_cache ? 0 : -ENOMEM; +} + +void wg_peer_uninit(void) +{ + kmem_cache_destroy(peer_cache); +} -- cgit v1.3.1