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/ref_tracker.c | 533 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 533 insertions(+) create mode 100644 lib/ref_tracker.c (limited to 'lib/ref_tracker.c') diff --git a/lib/ref_tracker.c b/lib/ref_tracker.c new file mode 100644 index 000000000..30c999d57 --- /dev/null +++ b/lib/ref_tracker.c @@ -0,0 +1,533 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#define pr_fmt(fmt) "ref_tracker: " fmt + +#include +#include +#include +#include +#include +#include +#include + +#define REF_TRACKER_STACK_ENTRIES 16 +#define STACK_BUF_SIZE 1024 + +struct ref_tracker { + struct list_head head; /* anchor into dir->list or dir->quarantine */ + bool dead; + depot_stack_handle_t alloc_stack_handle; + depot_stack_handle_t free_stack_handle; +}; + +struct ref_tracker_dir_stats { + int total; + int count; + struct { + depot_stack_handle_t stack_handle; + unsigned int count; + } stacks[]; +}; + +#ifdef CONFIG_DEBUG_FS +#include + +/* + * ref_tracker_dir_init() is usually called in allocation-safe contexts, but + * the same is not true of ref_tracker_dir_exit() which can be called from + * anywhere an object is freed. Removing debugfs dentries is a blocking + * operation, so we defer that work to the debugfs_reap_worker. + * + * Each dentry is tracked in the appropriate xarray. When + * ref_tracker_dir_exit() is called, its entries in the xarrays are marked and + * the workqueue job is scheduled. The worker then runs and deletes any marked + * dentries asynchronously. + */ +static struct xarray debugfs_dentries; +static struct xarray debugfs_symlinks; +static struct work_struct debugfs_reap_worker; + +#define REF_TRACKER_DIR_DEAD XA_MARK_0 +static inline void ref_tracker_debugfs_mark(struct ref_tracker_dir *dir) +{ + unsigned long flags; + + xa_lock_irqsave(&debugfs_dentries, flags); + __xa_set_mark(&debugfs_dentries, (unsigned long)dir, REF_TRACKER_DIR_DEAD); + xa_unlock_irqrestore(&debugfs_dentries, flags); + + xa_lock_irqsave(&debugfs_symlinks, flags); + __xa_set_mark(&debugfs_symlinks, (unsigned long)dir, REF_TRACKER_DIR_DEAD); + xa_unlock_irqrestore(&debugfs_symlinks, flags); + + schedule_work(&debugfs_reap_worker); +} +#else +static inline void ref_tracker_debugfs_mark(struct ref_tracker_dir *dir) +{ +} +#endif + +static struct ref_tracker_dir_stats * +ref_tracker_get_stats(struct ref_tracker_dir *dir, unsigned int limit) +{ + struct ref_tracker_dir_stats *stats; + struct ref_tracker *tracker; + + stats = kmalloc_flex(*stats, stacks, limit, GFP_NOWAIT); + if (!stats) + return ERR_PTR(-ENOMEM); + stats->total = 0; + stats->count = 0; + + list_for_each_entry(tracker, &dir->list, head) { + depot_stack_handle_t stack = tracker->alloc_stack_handle; + int i; + + ++stats->total; + for (i = 0; i < stats->count; ++i) + if (stats->stacks[i].stack_handle == stack) + break; + if (i >= limit) + continue; + if (i >= stats->count) { + stats->stacks[i].stack_handle = stack; + stats->stacks[i].count = 0; + ++stats->count; + } + ++stats->stacks[i].count; + } + + return stats; +} + +struct ostream { + void __ostream_printf (*func)(struct ostream *stream, char *fmt, ...); + char *prefix; + char *buf; + struct seq_file *seq; + int size, used; +}; + +static void __ostream_printf pr_ostream_log(struct ostream *stream, char *fmt, ...) +{ + va_list args; + + va_start(args, fmt); + vprintk(fmt, args); + va_end(args); +} + +static void __ostream_printf pr_ostream_buf(struct ostream *stream, char *fmt, ...) +{ + int ret, len = stream->size - stream->used; + va_list args; + + va_start(args, fmt); + ret = vsnprintf(stream->buf + stream->used, len, fmt, args); + va_end(args); + if (ret > 0) + stream->used += min(ret, len); +} + +#define pr_ostream(stream, fmt, args...) \ +({ \ + struct ostream *_s = (stream); \ +\ + _s->func(_s, fmt, ##args); \ +}) + +static void +__ref_tracker_dir_pr_ostream(struct ref_tracker_dir *dir, + unsigned int display_limit, struct ostream *s) +{ + struct ref_tracker_dir_stats *stats; + unsigned int i = 0, skipped; + depot_stack_handle_t stack; + char *sbuf; + + lockdep_assert_held(&dir->lock); + + if (list_empty(&dir->list)) + return; + + stats = ref_tracker_get_stats(dir, display_limit); + if (IS_ERR(stats)) { + pr_ostream(s, "%s%s@%p: couldn't get stats, error %pe\n", + s->prefix, dir->class, dir, stats); + return; + } + + sbuf = kmalloc(STACK_BUF_SIZE, GFP_NOWAIT); + + for (i = 0, skipped = stats->total; i < stats->count; ++i) { + stack = stats->stacks[i].stack_handle; + if (sbuf && !stack_depot_snprint(stack, sbuf, STACK_BUF_SIZE, 4)) + sbuf[0] = 0; + pr_ostream(s, "%s%s@%p has %d/%d users at\n%s\n", s->prefix, + dir->class, dir, stats->stacks[i].count, + stats->total, sbuf); + skipped -= stats->stacks[i].count; + } + + if (skipped) + pr_ostream(s, "%s%s@%p skipped reports about %d/%d users.\n", + s->prefix, dir->class, dir, skipped, stats->total); + + kfree(sbuf); + + kfree(stats); +} + +void ref_tracker_dir_print_locked(struct ref_tracker_dir *dir, + unsigned int display_limit) +{ + struct ostream os = { .func = pr_ostream_log, + .prefix = "ref_tracker: " }; + + __ref_tracker_dir_pr_ostream(dir, display_limit, &os); +} +EXPORT_SYMBOL(ref_tracker_dir_print_locked); + +void ref_tracker_dir_print(struct ref_tracker_dir *dir, + unsigned int display_limit) +{ + unsigned long flags; + + spin_lock_irqsave(&dir->lock, flags); + ref_tracker_dir_print_locked(dir, display_limit); + spin_unlock_irqrestore(&dir->lock, flags); +} +EXPORT_SYMBOL(ref_tracker_dir_print); + +int ref_tracker_dir_snprint(struct ref_tracker_dir *dir, char *buf, size_t size) +{ + struct ostream os = { .func = pr_ostream_buf, + .prefix = "ref_tracker: ", + .buf = buf, + .size = size }; + unsigned long flags; + + spin_lock_irqsave(&dir->lock, flags); + __ref_tracker_dir_pr_ostream(dir, 16, &os); + spin_unlock_irqrestore(&dir->lock, flags); + + return os.used; +} +EXPORT_SYMBOL(ref_tracker_dir_snprint); + +void ref_tracker_dir_exit(struct ref_tracker_dir *dir) +{ + struct ref_tracker *tracker, *n; + unsigned long flags; + bool leak = false; + + dir->dead = true; + /* + * The xarray entries must be marked before the dir->lock is taken to + * protect simultaneous debugfs readers. + */ + ref_tracker_debugfs_mark(dir); + spin_lock_irqsave(&dir->lock, flags); + list_for_each_entry_safe(tracker, n, &dir->quarantine, head) { + list_del(&tracker->head); + kfree(tracker); + dir->quarantine_avail++; + } + if (!list_empty(&dir->list)) { + ref_tracker_dir_print_locked(dir, 16); + leak = true; + list_for_each_entry_safe(tracker, n, &dir->list, head) { + list_del(&tracker->head); + kfree(tracker); + } + } + spin_unlock_irqrestore(&dir->lock, flags); + WARN_ON_ONCE(leak); + WARN_ON_ONCE(refcount_read(&dir->untracked) != 1); + WARN_ON_ONCE(refcount_read(&dir->no_tracker) != 1); +} +EXPORT_SYMBOL(ref_tracker_dir_exit); + +int ref_tracker_alloc(struct ref_tracker_dir *dir, + struct ref_tracker **trackerp, + gfp_t gfp) +{ + unsigned long entries[REF_TRACKER_STACK_ENTRIES]; + struct ref_tracker *tracker; + unsigned int nr_entries; + gfp_t gfp_mask = gfp | __GFP_NOWARN; + unsigned long flags; + + WARN_ON_ONCE(dir->dead); + + if (!trackerp) { + refcount_inc(&dir->no_tracker); + return 0; + } + if (gfp & __GFP_DIRECT_RECLAIM) + gfp_mask |= __GFP_NOFAIL; + *trackerp = tracker = kzalloc_obj(*tracker, gfp_mask); + if (unlikely(!tracker)) { + pr_err_once("memory allocation failure, unreliable refcount tracker.\n"); + refcount_inc(&dir->untracked); + return -ENOMEM; + } + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1); + tracker->alloc_stack_handle = stack_depot_save(entries, nr_entries, gfp); + + spin_lock_irqsave(&dir->lock, flags); + list_add(&tracker->head, &dir->list); + spin_unlock_irqrestore(&dir->lock, flags); + return 0; +} +EXPORT_SYMBOL_GPL(ref_tracker_alloc); + +int ref_tracker_free(struct ref_tracker_dir *dir, + struct ref_tracker **trackerp) +{ + unsigned long entries[REF_TRACKER_STACK_ENTRIES]; + depot_stack_handle_t stack_handle; + struct ref_tracker *tracker; + unsigned int nr_entries; + unsigned long flags; + + WARN_ON_ONCE(dir->dead); + + if (!trackerp) { + refcount_dec(&dir->no_tracker); + return 0; + } + tracker = *trackerp; + if (!tracker) { + refcount_dec(&dir->untracked); + return -EEXIST; + } + nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 1); + stack_handle = stack_depot_save(entries, nr_entries, + GFP_NOWAIT); + + spin_lock_irqsave(&dir->lock, flags); + if (tracker->dead) { + pr_err("reference already released.\n"); + if (tracker->alloc_stack_handle) { + pr_err("allocated in:\n"); + stack_depot_print(tracker->alloc_stack_handle); + } + if (tracker->free_stack_handle) { + pr_err("freed in:\n"); + stack_depot_print(tracker->free_stack_handle); + } + spin_unlock_irqrestore(&dir->lock, flags); + WARN_ON_ONCE(1); + return -EINVAL; + } + tracker->dead = true; + + tracker->free_stack_handle = stack_handle; + + list_move_tail(&tracker->head, &dir->quarantine); + if (!dir->quarantine_avail) { + tracker = list_first_entry(&dir->quarantine, struct ref_tracker, head); + list_del(&tracker->head); + } else { + dir->quarantine_avail--; + tracker = NULL; + } + spin_unlock_irqrestore(&dir->lock, flags); + + kfree(tracker); + return 0; +} +EXPORT_SYMBOL_GPL(ref_tracker_free); + +#ifdef CONFIG_DEBUG_FS +#include + +static struct dentry *ref_tracker_debug_dir = (struct dentry *)-ENOENT; + +static void __ostream_printf pr_ostream_seq(struct ostream *stream, char *fmt, ...) +{ + va_list args; + + va_start(args, fmt); + seq_vprintf(stream->seq, fmt, args); + va_end(args); +} + +static int ref_tracker_dir_seq_print(struct ref_tracker_dir *dir, struct seq_file *seq) +{ + struct ostream os = { .func = pr_ostream_seq, + .prefix = "", + .seq = seq }; + + __ref_tracker_dir_pr_ostream(dir, 16, &os); + + return os.used; +} + +static int ref_tracker_debugfs_show(struct seq_file *f, void *v) +{ + struct ref_tracker_dir *dir = f->private; + unsigned long index = (unsigned long)dir; + unsigned long flags; + int ret; + + /* + * "dir" may not exist at this point if ref_tracker_dir_exit() has + * already been called. Take care not to dereference it until its + * legitimacy is established. + * + * The xa_lock is necessary to ensure that "dir" doesn't disappear + * before its lock can be taken. If it's in the hash and not marked + * dead, then it's safe to take dir->lock which prevents + * ref_tracker_dir_exit() from completing. Once the dir->lock is + * acquired, the xa_lock can be released. All of this must be IRQ-safe. + */ + xa_lock_irqsave(&debugfs_dentries, flags); + if (!xa_load(&debugfs_dentries, index) || + xa_get_mark(&debugfs_dentries, index, REF_TRACKER_DIR_DEAD)) { + xa_unlock_irqrestore(&debugfs_dentries, flags); + return -ENODATA; + } + + spin_lock(&dir->lock); + xa_unlock(&debugfs_dentries); + ret = ref_tracker_dir_seq_print(dir, f); + spin_unlock_irqrestore(&dir->lock, flags); + return ret; +} + +static int ref_tracker_debugfs_open(struct inode *inode, struct file *filp) +{ + struct ref_tracker_dir *dir = inode->i_private; + + return single_open(filp, ref_tracker_debugfs_show, dir); +} + +static const struct file_operations ref_tracker_debugfs_fops = { + .owner = THIS_MODULE, + .open = ref_tracker_debugfs_open, + .read = seq_read, + .llseek = seq_lseek, + .release = single_release, +}; + +/** + * ref_tracker_dir_debugfs - create debugfs file for ref_tracker_dir + * @dir: ref_tracker_dir to be associated with debugfs file + * + * In most cases, a debugfs file will be created automatically for every + * ref_tracker_dir. If the object was created before debugfs is brought up + * then that may fail. In those cases, it is safe to call this at a later + * time to create the file. + */ +void ref_tracker_dir_debugfs(struct ref_tracker_dir *dir) +{ + char name[NAME_MAX + 1]; + struct dentry *dentry; + int ret; + + /* No-op if already created */ + dentry = xa_load(&debugfs_dentries, (unsigned long)dir); + if (dentry && !xa_is_err(dentry)) + return; + + ret = snprintf(name, sizeof(name), "%s@%p", dir->class, dir); + name[sizeof(name) - 1] = '\0'; + + if (ret < sizeof(name)) { + dentry = debugfs_create_file(name, S_IFREG | 0400, + ref_tracker_debug_dir, dir, + &ref_tracker_debugfs_fops); + if (!IS_ERR(dentry)) { + void *old; + + old = xa_store_irq(&debugfs_dentries, (unsigned long)dir, + dentry, GFP_KERNEL); + + if (xa_is_err(old)) + debugfs_remove(dentry); + else + WARN_ON_ONCE(old); + } + } +} +EXPORT_SYMBOL(ref_tracker_dir_debugfs); + +void __ostream_printf ref_tracker_dir_symlink(struct ref_tracker_dir *dir, const char *fmt, ...) +{ + char name[NAME_MAX + 1]; + struct dentry *symlink, *dentry; + va_list args; + int ret; + + symlink = xa_load(&debugfs_symlinks, (unsigned long)dir); + dentry = xa_load(&debugfs_dentries, (unsigned long)dir); + + /* Already created?*/ + if (symlink && !xa_is_err(symlink)) + return; + + if (!dentry || xa_is_err(dentry)) + return; + + va_start(args, fmt); + ret = vsnprintf(name, sizeof(name), fmt, args); + va_end(args); + name[sizeof(name) - 1] = '\0'; + + if (ret < sizeof(name)) { + symlink = debugfs_create_symlink(name, ref_tracker_debug_dir, + dentry->d_name.name); + if (!IS_ERR(symlink)) { + void *old; + + old = xa_store_irq(&debugfs_symlinks, (unsigned long)dir, + symlink, GFP_KERNEL); + if (xa_is_err(old)) + debugfs_remove(symlink); + else + WARN_ON_ONCE(old); + } + } +} +EXPORT_SYMBOL(ref_tracker_dir_symlink); + +static void debugfs_reap_work(struct work_struct *work) +{ + struct dentry *dentry; + unsigned long index; + bool reaped; + + do { + reaped = false; + xa_for_each_marked(&debugfs_symlinks, index, dentry, REF_TRACKER_DIR_DEAD) { + xa_erase_irq(&debugfs_symlinks, index); + debugfs_remove(dentry); + reaped = true; + } + xa_for_each_marked(&debugfs_dentries, index, dentry, REF_TRACKER_DIR_DEAD) { + xa_erase_irq(&debugfs_dentries, index); + debugfs_remove(dentry); + reaped = true; + } + } while (reaped); +} + +static int __init ref_tracker_debugfs_postcore_init(void) +{ + INIT_WORK(&debugfs_reap_worker, debugfs_reap_work); + xa_init_flags(&debugfs_dentries, XA_FLAGS_LOCK_IRQ); + xa_init_flags(&debugfs_symlinks, XA_FLAGS_LOCK_IRQ); + return 0; +} +postcore_initcall(ref_tracker_debugfs_postcore_init); + +static int __init ref_tracker_debugfs_late_init(void) +{ + ref_tracker_debug_dir = debugfs_create_dir("ref_tracker", NULL); + return 0; +} +late_initcall(ref_tracker_debugfs_late_init); +#endif /* CONFIG_DEBUG_FS */ -- cgit v1.3.1