uprobes: Introduce uprobe_apply()

Currently it is not possible to change the filtering constraints after
uprobe_register(), so a consumer can not, say, start to trace a task/mm
which was previously filtered out, or remove the no longer needed bp's.

Introduce uprobe_apply() which simply does register_for_each_vma() again
to consult uprobe_consumer->filter() and install/remove the breakpoints.
The only complication is that register_for_each_vma() can no longer
assume that uprobe->consumers should be consulter if is_register == T,
so we change it to accept "struct uprobe_consumer *new" instead.

Unlike uprobe_register(), uprobe_apply(true) doesn't do "unregister" if
register_for_each_vma() fails, it is up to caller to handle the error.

Note: we probably need to cleanup the current interface, it is strange
that uprobe_apply/unregister need inode/offset. We should either change
uprobe_register() to return "struct uprobe *", or add a private ->uprobe
member in uprobe_consumer. And in the long term uprobe_apply() should
take a single argument, uprobe or consumer, even "bool add" should go
away.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

1 files changed, 35 insertions, 4 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 221fc58f59e3..a567c8c7ef31 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -733,8 +733,10 @@ build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
         return curr;
 }
 
-static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
+static int
+register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new)
 {
+        bool is_register = !!new;
         struct map_info *info;
         int err = 0;
 
@@ -765,7 +767,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
 
                 if (is_register) {
                         /* consult only the "caller", new consumer. */
-                        if (consumer_filter(uprobe->consumers,
+                        if (consumer_filter(new,
                                         UPROBE_FILTER_REGISTER, mm))
                                 err = install_breakpoint(uprobe, mm, vma, info->vaddr);
                 } else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
@@ -788,7 +790,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
 static int __uprobe_register(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
         consumer_add(uprobe, uc);
-        return register_for_each_vma(uprobe, true);
+        return register_for_each_vma(uprobe, uc);
 }
 
 static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
@@ -798,7 +800,7 @@ static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *u
         if (!consumer_del(uprobe, uc))  /* WARN? */
                 return;
 
-        err = register_for_each_vma(uprobe, false);
+        err = register_for_each_vma(uprobe, NULL);
         /* TODO : cant unregister? schedule a worker thread */
         if (!uprobe->consumers && !err)
                 delete_uprobe(uprobe);
@@ -855,6 +857,35 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
 EXPORT_SYMBOL_GPL(uprobe_register);
 
 /*
+ * uprobe_apply - unregister a already registered probe.
+ * @inode: the file in which the probe has to be removed.
+ * @offset: offset from the start of the file.
+ * @uc: consumer which wants to add more or remove some breakpoints
+ * @add: add or remove the breakpoints
+ */
+int uprobe_apply(struct inode *inode, loff_t offset,
+                        struct uprobe_consumer *uc, bool add)
+{
+        struct uprobe *uprobe;
+        struct uprobe_consumer *con;
+        int ret = -ENOENT;
+
+        uprobe = find_uprobe(inode, offset);
+        if (!uprobe)
+                return ret;
+
+        down_write(&uprobe->register_rwsem);
+        for (con = uprobe->consumers; con && con != uc ; con = con->next)
+                ;
+        if (con)
+                ret = register_for_each_vma(uprobe, add ? uc : NULL);
+        up_write(&uprobe->register_rwsem);
+        put_uprobe(uprobe);
+
+        return ret;
+}
+
+/*
  * uprobe_unregister - unregister a already registered probe.
  * @inode: the file in which the probe has to be removed.
  * @offset: offset from the start of the file.