uprobes: Teach handler_chain() to filter out the probed task

Currrently the are 2 problems with pre-filtering:

1. It is not possible to add/remove a task (mm) after uprobe_register()

2. A forked child inherits all breakpoints and uprobe_consumer can not
   control this.

This patch does the first step to improve the filtering. handler_chain()
removes the breakpoints installed by this uprobe from current->mm if all
handlers return UPROBE_HANDLER_REMOVE.

Note that handler_chain() relies on ->register_rwsem to avoid the race
with uprobe_register/unregister which can add/del a consumer, or even
remove and then insert the new uprobe at the same address.

Perhaps we will add uprobe_apply_mm(uprobe, mm, is_register) and teach
copy_mm() to do filter(UPROBE_FILTER_FORK), but I think this change makes
sense anyway.

Note: instead of checking the retcode from uc->handler, we could add
uc->filter(UPROBE_FILTER_BPHIT). But I think this is not optimal to
call 2 hooks in a row. This buys nothing, and if handler/filter do
something nontrivial they will probably do the same work twice.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

2 files changed, 51 insertions, 10 deletions

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index c2df6934fdc6..95d0002efda5 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -35,6 +35,9 @@ struct inode;
 # include <asm/uprobes.h>
 #endif
 
+#define UPROBE_HANDLER_REMOVE           1
+#define UPROBE_HANDLER_MASK             1
+
 enum uprobe_filter_ctx {
         UPROBE_FILTER_REGISTER,
         UPROBE_FILTER_UNREGISTER,
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index c2737be3c4b8..04c104ad9522 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -440,16 +440,6 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
         return uprobe;
 }
 
-static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
-{
-        struct uprobe_consumer *uc;
-
-        down_read(&uprobe->register_rwsem);
-        for (uc = uprobe->consumers; uc; uc = uc->next)
-                uc->handler(uc, regs);
-        up_read(&uprobe->register_rwsem);
-}
-
 static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
         down_write(&uprobe->consumer_rwsem);
@@ -882,6 +872,33 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume
         put_uprobe(uprobe);
 }
 
+static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
+{
+        struct vm_area_struct *vma;
+        int err = 0;
+
+        down_read(&mm->mmap_sem);
+        for (vma = mm->mmap; vma; vma = vma->vm_next) {
+                unsigned long vaddr;
+                loff_t offset;
+
+                if (!valid_vma(vma, false) ||
+                    vma->vm_file->f_mapping->host != uprobe->inode)
+                        continue;
+
+                offset = (loff_t)vma->vm_pgoff << PAGE_SHIFT;
+                if (uprobe->offset <  offset ||
+                    uprobe->offset >= offset + vma->vm_end - vma->vm_start)
+                        continue;
+
+                vaddr = offset_to_vaddr(vma, uprobe->offset);
+                err |= remove_breakpoint(uprobe, mm, vaddr);
+        }
+        up_read(&mm->mmap_sem);
+
+        return err;
+}
+
 static struct rb_node *
 find_node_in_range(struct inode *inode, loff_t min, loff_t max)
 {
@@ -1435,6 +1452,27 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
         return uprobe;
 }
 
+static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
+{
+        struct uprobe_consumer *uc;
+        int remove = UPROBE_HANDLER_REMOVE;
+
+        down_read(&uprobe->register_rwsem);
+        for (uc = uprobe->consumers; uc; uc = uc->next) {
+                int rc = uc->handler(uc, regs);
+
+                WARN(rc & ~UPROBE_HANDLER_MASK,
+                        "bad rc=0x%x from %pf()\n", rc, uc->handler);
+                remove &= rc;
+        }
+
+        if (remove && uprobe->consumers) {
+                WARN_ON(!uprobe_is_active(uprobe));
+                unapply_uprobe(uprobe, current->mm);
+        }
+        up_read(&uprobe->register_rwsem);
+}
+
 /*
  * Run handler and ask thread to singlestep.
  * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.