4.9-stable review patch. If anyone has any objections, please let me know.
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From: Lars-Peter Clausen lars@metafoo.de
[ Upstream commit 4058ebf33cb0be88ca516f968eda24ab7b6b93e4 ]
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 [...] [<ffffff800847b790>] __arch_copy_to_user+0x190/0x220 [<ffffff80086f25d8>] ffs_user_copy_worker+0x70/0x130 [<ffffff80080b8c64>] process_one_work+0x1dc/0x460 [<ffffff80080b8f38>] worker_thread+0x50/0x4b0 [<ffffff80080bf5a0>] kthread+0xd8/0xf0 [<ffffff8008083680>] 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 lars@metafoo.de Signed-off-by: Felipe Balbi felipe.balbi@linux.intel.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/gadget/function/f_fs.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -759,9 +759,13 @@ static void ffs_user_copy_worker(struct 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);