Re: [PATCH] uprobes: list all active uprobes in the system

[Ian Rogers]

On Wed, Jan 11, 2023 at 2:49 AM <luolongjun@xxxxxxxxxx> wrote:
>
> From: Longjun Luo <luolongjun@xxxxxxxxxx>
>
> Since uprobes will replace instructions in the process
> memory, it is necessary to provide one way to list
> all active uprobes. One can access this file through
> /sys/kernel/debug/uprobes/list.
>
> Output looks like this
> =====================
> inode+offset/ref_ctr_offset    4160760670+0x30a10/0x0
>     ref                        1
>     register_rwsem             (unlocked)
>     consumer_rwsem             (unlocked)
>     consumers-1
>         handler                0xffffffffc03ee02e(handler) uprobe
>         ret_handler            0x0000000000000000( )
>         filter                 0xffffffffc03ee010(filter) uprobe
>     consumers-2
>         handler                0xffffffffc03e902e(handler_1) uprobe_1
>         ret_handler            0x0000000000000000( )
>         filter                 0xffffffffc03e9010(filter_1) uprobe_1
>
> Signed-off-by: Longjun Luo <luolongjun@xxxxxxxxxx>
> ---
>  kernel/events/uprobes.c | 120 ++++++++++++++++++++++++++++++++++++----
>  1 file changed, 109 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index d9e357b7e17c..2fa9b910abc7 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -27,6 +27,9 @@
>  #include <linux/task_work.h>
>  #include <linux/shmem_fs.h>
>  #include <linux/khugepaged.h>
> +#include <linux/rbtree.h>
> +#include <linux/debugfs.h>
> +#include <linux/kallsyms.h>
>
>  #include <linux/uprobes.h>
>
> @@ -40,7 +43,7 @@ static struct rb_root uprobes_tree = RB_ROOT;
>   */
>  #define no_uprobe_events()     RB_EMPTY_ROOT(&uprobes_tree)
>
> -static DEFINE_SPINLOCK(uprobes_treelock);      /* serialize rbtree access */
> +static DECLARE_RWSEM(uprobes_treelock);        /* serialize rbtree access */
>
>  #define UPROBES_HASH_SZ        13
>  /* serialize uprobe->pending_list */
> @@ -672,9 +675,9 @@ static struct uprobe *find_uprobe(struct inode *inode, loff_t offset)
>  {
>         struct uprobe *uprobe;
>
> -       spin_lock(&uprobes_treelock);
> +       down_read(&uprobes_treelock);
>         uprobe = __find_uprobe(inode, offset);
> -       spin_unlock(&uprobes_treelock);
> +       up_read(&uprobes_treelock);
>
>         return uprobe;
>  }
> @@ -704,9 +707,9 @@ static struct uprobe *insert_uprobe(struct uprobe *uprobe)
>  {
>         struct uprobe *u;
>
> -       spin_lock(&uprobes_treelock);
> +       down_write(&uprobes_treelock);
>         u = __insert_uprobe(uprobe);
> -       spin_unlock(&uprobes_treelock);
> +       up_write(&uprobes_treelock);
>
>         return u;
>  }
> @@ -938,9 +941,9 @@ static void delete_uprobe(struct uprobe *uprobe)
>         if (WARN_ON(!uprobe_is_active(uprobe)))
>                 return;
>
> -       spin_lock(&uprobes_treelock);
> +       down_write(&uprobes_treelock);
>         rb_erase(&uprobe->rb_node, &uprobes_tree);
> -       spin_unlock(&uprobes_treelock);
> +       up_write(&uprobes_treelock);
>         RB_CLEAR_NODE(&uprobe->rb_node); /* for uprobe_is_active() */
>         put_uprobe(uprobe);
>  }
> @@ -1301,7 +1304,7 @@ static void build_probe_list(struct inode *inode,
>         min = vaddr_to_offset(vma, start);
>         max = min + (end - start) - 1;
>
> -       spin_lock(&uprobes_treelock);
> +       down_read(&uprobes_treelock);
>         n = find_node_in_range(inode, min, max);
>         if (n) {
>                 for (t = n; t; t = rb_prev(t)) {
> @@ -1319,7 +1322,7 @@ static void build_probe_list(struct inode *inode,
>                         get_uprobe(u);
>                 }
>         }
> -       spin_unlock(&uprobes_treelock);
> +       up_read(&uprobes_treelock);
>  }
>
>  /* @vma contains reference counter, not the probed instruction. */
> @@ -1410,9 +1413,9 @@ vma_has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long e
>         min = vaddr_to_offset(vma, start);
>         max = min + (end - start) - 1;
>
> -       spin_lock(&uprobes_treelock);
> +       down_read(&uprobes_treelock);
>         n = find_node_in_range(inode, min, max);
> -       spin_unlock(&uprobes_treelock);
> +       up_read(&uprobes_treelock);
>
>         return !!n;
>  }
> @@ -2357,3 +2360,98 @@ void __init uprobes_init(void)
>
>         BUG_ON(register_die_notifier(&uprobe_exception_nb));
>  }
> +
> +#ifdef CONFIG_DEBUG_FS
> +
> +static void *uprobe_seq_start(struct seq_file *m, loff_t *pos)
> +{
> +       loff_t num = *pos;
> +       struct rb_node *rbp;
> +
> +       down_read(&uprobes_treelock);

Is there a missing corresponding up_read?

Thanks,
Ian

> +       for (rbp = rb_first(&uprobes_tree); rbp; rbp = rb_next(rbp)) {
> +               if (num-- == 0)
> +                       return rbp;
> +       }
> +
> +       return NULL;
> +}
> +
> +static void *uprobe_seq_next(struct seq_file *f, void *v, loff_t *pos)
> +{
> +       ++*pos;
> +       return (void *)rb_next(v);
> +}
> +
> +static void uprobe_seq_stop(struct seq_file *f, void *v)
> +{
> +       up_read(&uprobes_treelock);
> +}
> +
> +static int show_uprobe(struct seq_file *m, void *v)
> +{
> +       struct uprobe *uprobe = rb_entry_safe(v, struct uprobe, rb_node);
> +       struct uprobe_consumer *con;
> +       char *modname, namebuf[KSYM_NAME_LEN];
> +       const char *sym;
> +       unsigned int cnt = 1;
> +
> +       seq_printf(m, "inode+offset/ref_ctr_offset    %lu+0x%llx/0x%llx\n",
> +               uprobe->inode->i_ino, uprobe->offset, uprobe->ref_ctr_offset);
> +       seq_printf(m, "    ref                        %u\n",
> +               refcount_read(&uprobe->ref));
> +       seq_printf(m, "    register_rwsem             %s\n",
> +               rwsem_is_locked(&uprobe->register_rwsem)?"(locked)":"(unlocked)");
> +       seq_printf(m, "    consumer_rwsem             %s\n",
> +               rwsem_is_locked(&uprobe->consumer_rwsem)?"(locked)":"(unlocked)");
> +
> +       /* lock consumer_rwsem when hold uprobes_treelock */
> +       down_read(&uprobe->consumer_rwsem);
> +       for (con = uprobe->consumers; con; con = con->next, cnt++) {
> +               seq_printf(m, "    consumers-%u\n", cnt);
> +
> +               modname = NULL;
> +               sym = kallsyms_lookup((unsigned long)con->handler, NULL, NULL,
> +                       &modname, namebuf);
> +               seq_printf(m, "        handler                0x%px(%s) %s\n",
> +                       con->handler, (sym ? sym : " "), (modname ? modname : " "));
> +
> +               modname = NULL;
> +               sym = kallsyms_lookup((unsigned long)con->ret_handler, NULL, NULL,
> +                       &modname, namebuf);
> +               seq_printf(m, "        ret_handler            0x%px(%s) %s\n",
> +                       con->ret_handler, (sym ? sym : " "), (modname ? modname : " "));
> +
> +               modname = NULL;
> +               sym = kallsyms_lookup((unsigned long)con->filter, NULL, NULL,
> +                       &modname, namebuf);
> +               seq_printf(m, "        filter                 0x%px(%s) %s\n",
> +                       con->filter, (sym ? sym : " "), (modname ? modname : " "));
> +       }
> +       up_read(&uprobe->consumer_rwsem);
> +
> +       return 0;
> +}
> +
> +static const struct seq_operations uprobes_sops = {
> +       .start = uprobe_seq_start,
> +       .next  = uprobe_seq_next,
> +       .stop  = uprobe_seq_stop,
> +       .show  = show_uprobe,
> +};
> +
> +DEFINE_SEQ_ATTRIBUTE(uprobes);
> +
> +static int __init debugfs_uprobe_init(void)
> +{
> +       struct dentry *dir;
> +
> +       dir = debugfs_create_dir("uprobes", NULL);
> +
> +       debugfs_create_file("list", 0400, dir, NULL, &uprobes_fops);
> +
> +       return 0;
> +}
> +late_initcall(debugfs_uprobe_init);
> +
> +#endif /* CONFIG_DEBUG_FS */
> --
> 2.38.1
>