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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>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.