From ddac7d5fba555967654bf47b7b458b050391dc1f Mon Sep 17 00:00:00 2001 From: Vinayak Menon Date: Mon, 2 Jun 2014 18:17:59 +0530 Subject: [PATCH] staging: binder: add vm_fault handler An issue was observed when a userspace task exits. The page which hits error here is the zero page. In binder mmap, the whole of vma is not mapped. On a task crash, when debuggerd reads the binder regions, the unmapped areas fall to do_anonymous_page in handle_pte_fault, due to the absence of a vm_fault handler. This results in zero page being mapped. Later in zap_pte_range, vm_normal_page returns zero page in the case of VM_MIXEDMAP and it results in the error. BUG: Bad page map in process mediaserver pte:9dff379f pmd:9bfbd831 page:c0ed8e60 count:1 mapcount:-1 mapping: (null) index:0x0 page flags: 0x404(referenced|reserved) addr:40c3f000 vm_flags:10220051 anon_vma: (null) mapping:d9fe0764 index:fd vma->vm_ops->fault: (null) vma->vm_file->f_op->mmap: binder_mmap+0x0/0x274 CPU: 0 PID: 1463 Comm: mediaserver Tainted: G W 3.10.17+ #1 [] (unwind_backtrace+0x0/0x11c) from [] (show_stack+0x10/0x14) [] (show_stack+0x10/0x14) from [] (print_bad_pte+0x158/0x190) [] (print_bad_pte+0x158/0x190) from [] (unmap_single_vma+0x2e4/0x598) [] (unmap_single_vma+0x2e4/0x598) from [] (unmap_vmas+0x34/0x50) [] (unmap_vmas+0x34/0x50) from [] (exit_mmap+0xc8/0x1e8) [] (exit_mmap+0xc8/0x1e8) from [] (mmput+0x54/0xd0) [] (mmput+0x54/0xd0) from [] (do_exit+0x360/0x990) [] (do_exit+0x360/0x990) from [] (do_group_exit+0x84/0xc0) [] (do_group_exit+0x84/0xc0) from [] (get_signal_to_deliver+0x4d4/0x548) [] (get_signal_to_deliver+0x4d4/0x548) from [] (do_signal+0xa8/0x3b8) Add a vm_fault handler which returns VM_FAULT_SIGBUS, and prevents the wrong fallback to do_anonymous_page. Signed-off-by: Vinayak Menon Signed-off-by: Greg Kroah-Hartman --- drivers/staging/android/binder.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/staging/android/binder.c b/drivers/staging/android/binder.c index 589cfc8..2f38e44 100644 --- a/drivers/staging/android/binder.c +++ b/drivers/staging/android/binder.c @@ -2768,9 +2768,15 @@ static void binder_vma_close(struct vm_area_struct *vma) binder_defer_work(proc, BINDER_DEFERRED_PUT_FILES); } +static int binder_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf) +{ + return VM_FAULT_SIGBUS; +} + static struct vm_operations_struct binder_vm_ops = { .open = binder_vma_open, .close = binder_vma_close, + .fault = binder_vm_fault, }; static int binder_mmap(struct file *filp, struct vm_area_struct *vma) -- 2.7.4