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 --- lib/closure.c | 297 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 297 insertions(+) create mode 100644 lib/closure.c (limited to 'lib/closure.c') diff --git a/lib/closure.c b/lib/closure.c new file mode 100644 index 000000000..2bfe7d2a0 --- /dev/null +++ b/lib/closure.c @@ -0,0 +1,297 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Asynchronous refcounty things + * + * Copyright 2010, 2011 Kent Overstreet + * Copyright 2012 Google, Inc. + */ + +#include +#include +#include +#include +#include +#include + +static inline void closure_put_after_sub_checks(int flags) +{ + int r = flags & CLOSURE_REMAINING_MASK; + + if (WARN(flags & CLOSURE_GUARD_MASK, + "closure has guard bits set: %x (%u)", + flags & CLOSURE_GUARD_MASK, (unsigned) __fls(r))) + r &= ~CLOSURE_GUARD_MASK; + + WARN(!r && (flags & ~CLOSURE_DESTRUCTOR), + "closure ref hit 0 with incorrect flags set: %x (%u)", + flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags)); +} + +static inline void closure_put_after_sub(struct closure *cl, int flags) +{ + closure_put_after_sub_checks(flags); + + if (!(flags & CLOSURE_REMAINING_MASK)) { + smp_acquire__after_ctrl_dep(); + + cl->closure_get_happened = false; + + if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) { + atomic_set(&cl->remaining, + CLOSURE_REMAINING_INITIALIZER); + closure_queue(cl); + } else { + struct closure *parent = cl->parent; + closure_fn *destructor = cl->fn; + + closure_debug_destroy(cl); + + if (destructor) + destructor(&cl->work); + + if (parent) + closure_put(parent); + } + } +} + +/* For clearing flags with the same atomic op as a put */ +void closure_sub(struct closure *cl, int v) +{ + closure_put_after_sub(cl, atomic_sub_return_release(v, &cl->remaining)); +} +EXPORT_SYMBOL(closure_sub); + +/* + * closure_put - decrement a closure's refcount + */ +void closure_put(struct closure *cl) +{ + closure_put_after_sub(cl, atomic_dec_return_release(&cl->remaining)); +} +EXPORT_SYMBOL(closure_put); + +/* + * closure_wake_up - wake up all closures on a wait list, without memory barrier + */ +void __closure_wake_up(struct closure_waitlist *wait_list) +{ + struct llist_node *list; + struct closure *cl, *t; + struct llist_node *reverse = NULL; + + list = llist_del_all(&wait_list->list); + + /* We first reverse the list to preserve FIFO ordering and fairness */ + reverse = llist_reverse_order(list); + + /* Then do the wakeups */ + llist_for_each_entry_safe(cl, t, reverse, list) { + closure_set_waiting(cl, 0); + closure_sub(cl, CLOSURE_WAITING + 1); + } +} +EXPORT_SYMBOL(__closure_wake_up); + +/** + * closure_wait - add a closure to a waitlist + * @waitlist: will own a ref on @cl, which will be released when + * closure_wake_up() is called on @waitlist. + * @cl: closure pointer. + * + */ +bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl) +{ + if (atomic_read(&cl->remaining) & CLOSURE_WAITING) + return false; + + cl->closure_get_happened = true; + closure_set_waiting(cl, _RET_IP_); + atomic_add(CLOSURE_WAITING + 1, &cl->remaining); + llist_add(&cl->list, &waitlist->list); + + return true; +} +EXPORT_SYMBOL(closure_wait); + +struct closure_syncer { + struct task_struct *task; + int done; +}; + +static CLOSURE_CALLBACK(closure_sync_fn) +{ + struct closure *cl = container_of(ws, struct closure, work); + struct closure_syncer *s = cl->s; + struct task_struct *p; + + rcu_read_lock(); + p = READ_ONCE(s->task); + s->done = 1; + wake_up_process(p); + rcu_read_unlock(); +} + +void __sched __closure_sync(struct closure *cl) +{ + struct closure_syncer s = { .task = current }; + + cl->s = &s; + continue_at(cl, closure_sync_fn, NULL); + + while (1) { + set_current_state(TASK_UNINTERRUPTIBLE); + if (s.done) + break; + schedule(); + } + + __set_current_state(TASK_RUNNING); +} +EXPORT_SYMBOL(__closure_sync); + +/* + * closure_return_sync - finish running a closure, synchronously (i.e. waiting + * for outstanding get()s to finish) and returning once closure refcount is 0. + * + * Unlike closure_sync() this doesn't reinit the ref to 1; subsequent + * closure_get_not_zero() calls waill fail. + */ +void __sched closure_return_sync(struct closure *cl) +{ + struct closure_syncer s = { .task = current }; + + cl->s = &s; + set_closure_fn(cl, closure_sync_fn, NULL); + + unsigned flags = atomic_sub_return_release(1 + CLOSURE_RUNNING - CLOSURE_DESTRUCTOR, + &cl->remaining); + + closure_put_after_sub_checks(flags); + + if (unlikely(flags & CLOSURE_REMAINING_MASK)) { + while (1) { + set_current_state(TASK_UNINTERRUPTIBLE); + if (s.done) + break; + schedule(); + } + + __set_current_state(TASK_RUNNING); + } + + if (cl->parent) + closure_put(cl->parent); +} +EXPORT_SYMBOL(closure_return_sync); + +int __sched __closure_sync_timeout(struct closure *cl, unsigned long timeout) +{ + struct closure_syncer s = { .task = current }; + int ret = 0; + + cl->s = &s; + continue_at(cl, closure_sync_fn, NULL); + + while (1) { + set_current_state(TASK_UNINTERRUPTIBLE); + if (s.done) + break; + if (!timeout) { + /* + * Carefully undo the continue_at() - but only if it + * hasn't completed, i.e. the final closure_put() hasn't + * happened yet: + */ + unsigned old, new, v = atomic_read(&cl->remaining); + do { + old = v; + if (!old || (old & CLOSURE_RUNNING)) + goto success; + + new = old + CLOSURE_REMAINING_INITIALIZER; + } while ((v = atomic_cmpxchg(&cl->remaining, old, new)) != old); + ret = -ETIME; + } + + timeout = schedule_timeout(timeout); + } +success: + __set_current_state(TASK_RUNNING); + return ret; +} +EXPORT_SYMBOL(__closure_sync_timeout); + +#ifdef CONFIG_DEBUG_CLOSURES + +static LIST_HEAD(closure_list); +static DEFINE_SPINLOCK(closure_list_lock); + +void closure_debug_create(struct closure *cl) +{ + unsigned long flags; + + BUG_ON(cl->magic == CLOSURE_MAGIC_ALIVE); + cl->magic = CLOSURE_MAGIC_ALIVE; + + spin_lock_irqsave(&closure_list_lock, flags); + list_add(&cl->all, &closure_list); + spin_unlock_irqrestore(&closure_list_lock, flags); +} +EXPORT_SYMBOL(closure_debug_create); + +void closure_debug_destroy(struct closure *cl) +{ + unsigned long flags; + + if (cl->magic == CLOSURE_MAGIC_STACK) + return; + + BUG_ON(cl->magic != CLOSURE_MAGIC_ALIVE); + cl->magic = CLOSURE_MAGIC_DEAD; + + spin_lock_irqsave(&closure_list_lock, flags); + list_del(&cl->all); + spin_unlock_irqrestore(&closure_list_lock, flags); +} +EXPORT_SYMBOL(closure_debug_destroy); + +static int debug_show(struct seq_file *f, void *data) +{ + struct closure *cl; + + spin_lock_irq(&closure_list_lock); + + list_for_each_entry(cl, &closure_list, all) { + int r = atomic_read(&cl->remaining); + + seq_printf(f, "%p: %pS -> %pS p %p r %i ", + cl, (void *) cl->ip, cl->fn, cl->parent, + r & CLOSURE_REMAINING_MASK); + + seq_printf(f, "%s%s\n", + test_bit(WORK_STRUCT_PENDING_BIT, + work_data_bits(&cl->work)) ? "Q" : "", + r & CLOSURE_RUNNING ? "R" : ""); + + if (r & CLOSURE_WAITING) + seq_printf(f, " W %pS\n", + (void *) cl->waiting_on); + + seq_putc(f, '\n'); + } + + spin_unlock_irq(&closure_list_lock); + return 0; +} + +DEFINE_SHOW_ATTRIBUTE(debug); + +static int __init closure_debug_init(void) +{ + debugfs_create_file("closures", 0400, NULL, NULL, &debug_fops); + return 0; +} +late_initcall(closure_debug_init) + +#endif -- cgit v1.3.1