uprobes: Kill set_orig_insn()->is_swbp_at_addr()

Unlike set_swbp(), set_orig_insn()->is_swbp_at_addr() makes sense,
although it can't prevent all confusions.

But the usage of is_swbp_at_addr() is equally confusing, and it adds
the extra get_user_pages() we can avoid.

This patch removes set_orig_insn()->is_swbp_at_addr() but changes
write_opcode() to do the necessary checks before replace_page().

Perhaps it also makes sense to ensure PAGE_MAPPING_ANON in unregister
case.

find_active_uprobe() becomes the only user of is_swbp_at_addr(),
we can change its semantics.

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

1 files changed, 23 insertions, 9 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index b6f0f716a884..9248ee76b4bb 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -190,6 +190,25 @@ static void copy_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t
         kunmap_atomic(kaddr);
 }
 
+static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode)
+{
+        uprobe_opcode_t old_opcode;
+        bool is_swbp;
+
+        copy_opcode(page, vaddr, &old_opcode);
+        is_swbp = is_swbp_insn(&old_opcode);
+
+        if (is_swbp_insn(new_opcode)) {
+                if (is_swbp)            /* register: already installed? */
+                        return 0;
+        } else {
+                if (!is_swbp)           /* unregister: was it changed by us? */
+                        return -EINVAL;
+        }
+
+        return 1;
+}
+
 /*
  * NOTE:
  * Expect the breakpoint instruction to be the smallest size instruction for
@@ -226,6 +245,10 @@ retry:
         if (ret <= 0)
                 return ret;
 
+        ret = verify_opcode(old_page, vaddr, &opcode);
+        if (ret <= 0)
+                goto put_old;
+
         ret = -ENOMEM;
         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
         if (!new_page)
@@ -311,15 +334,6 @@ int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned
 int __weak
 set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
 {
-        int result;
-
-        result = is_swbp_at_addr(mm, vaddr);
-        if (!result)
-                return -EINVAL;
-
-        if (result != 1)
-                return result;
-
         return write_opcode(mm, vaddr, *(uprobe_opcode_t *)auprobe->insn);
 }