From 4058ebf33cb0be88ca516f968eda24ab7b6b93e4 Mon Sep 17 00:00:00 2001 From: Lars-Peter Clausen Date: Fri, 12 Jan 2018 11:05:02 +0100 Subject: [PATCH] usb: gadget: ffs: Execute copy_to_user() with USER_DS set When using a AIO read() operation on the function FS gadget driver a URB is submitted asynchronously and on URB completion the received data is copied to the userspace buffer associated with the read operation. This is done from a kernel worker thread invoking copy_to_user() (through copy_to_iter()). And while the user space process memory is made available to the kernel thread using use_mm(), some architecture require in addition to this that the operation runs with USER_DS set. Otherwise the userspace memory access will fail. For example on ARM64 with Privileged Access Never (PAN) and User Access Override (UAO) enabled the following crash occurs. Internal error: Accessing user space memory with fs=KERNEL_DS: 9600004f [#1] SMP Modules linked in: CPU: 2 PID: 1636 Comm: kworker/2:1 Not tainted 4.9.0-04081-g8ab2dfb-dirty #487 Hardware name: ZynqMP ZCU102 Rev1.0 (DT) Workqueue: events ffs_user_copy_worker task: ffffffc87afc8080 task.stack: ffffffc87a00c000 PC is at __arch_copy_to_user+0x190/0x220 LR is at copy_to_iter+0x78/0x3c8 [...] [] __arch_copy_to_user+0x190/0x220 [] ffs_user_copy_worker+0x70/0x130 [] process_one_work+0x1dc/0x460 [] worker_thread+0x50/0x4b0 [] kthread+0xd8/0xf0 [] ret_from_fork+0x10/0x50 Address this by placing a set_fs(USER_DS) before of the copy operation and revert it again once the copy operation has finished. This patch is analogous to commit d7ffde35e31a ("vhost: use USER_DS in vhost_worker thread") which addresses the same underlying issue. Signed-off-by: Lars-Peter Clausen Signed-off-by: Felipe Balbi --- drivers/usb/gadget/function/f_fs.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index c2592d8..e33e8ca 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -758,9 +758,13 @@ static void ffs_user_copy_worker(struct work_struct *work) bool kiocb_has_eventfd = io_data->kiocb->ki_flags & IOCB_EVENTFD; if (io_data->read && ret > 0) { + mm_segment_t oldfs = get_fs(); + + set_fs(USER_DS); use_mm(io_data->mm); ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data); unuse_mm(io_data->mm); + set_fs(oldfs); } io_data->kiocb->ki_complete(io_data->kiocb, ret, ret); -- 2.7.4