uprobes: Remove breakpoint in unapply_uprobe under mmap_write_lock

Currently unapply_uprobe takes mmap_read_lock, but it might call
remove_breakpoint which eventually changes user pages.

Current code writes either breakpoint or original instruction, so it can
go away with read lock as explained in here [1]. But with the upcoming
change that writes multiple instructions on the probed address we need
to ensure that any update to mm's pages is exclusive.

[1] https://lore.kernel.org/all/20240710140045.GA1084@redhat.com/

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20250720112133.244369-2-jolsa@kernel.org

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 7ca1940607bd8340d2f4d1b74faccd40c1cfdc70..1cbfe3cfe57385f6982c2f8c006ea53718a1fdb2 100644 (file)
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -482,7 +482,7 @@ remap:
  * @opcode_vaddr: the virtual address to store the opcode.
  * @opcode: opcode to be written at @opcode_vaddr.
  *
- * Called with mm->mmap_lock held for read or write.
+ * Called with mm->mmap_lock held for write.
  * Return 0 (success) or a negative errno.
  */
 int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
@@ -1463,7 +1463,7 @@ static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
        struct vm_area_struct *vma;
        int err = 0;
 
-       mmap_read_lock(mm);
+       mmap_write_lock(mm);
        for_each_vma(vmi, vma) {
                unsigned long vaddr;
                loff_t offset;
@@ -1480,7 +1480,7 @@ static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
                vaddr = offset_to_vaddr(vma, uprobe->offset);
                err |= remove_breakpoint(uprobe, vma, vaddr);
        }
-       mmap_read_unlock(mm);
+       mmap_write_unlock(mm);
 
        return err;
 }