On Thu, 15 Aug 2019, Jonathan Bell wrote: > On Thu, Aug 15, 2019 at 11:55 AM Oliver Neukum <oneu...@suse.com> wrote: > > > > Am Mittwoch, den 14.08.2019, 16:59 +0100 schrieb Jonathan Bell: > > > As reported by one of our users here: > > > https://github.com/raspberrypi/linux/issues/3148 > > > > > > There is a bug when the dwc2 core receives USB data packets that are > > > between 1 and 4 bytes in length - 4 bytes are always written to memory > > > where the non-packet bytes are garbage. > > > > Hi, > > > > in which function does that happen? If your buffer cannot handle 4 > > bytes I cannot see how it copes with teh DMA rules. > > > In drivers/media/usb/uvc/uvc_ctrl.c:uvc_ctrl_populate_cache() and friends. > > The UVC driver passes in offsets into a struct uvc_control as the > "buffer" that usb_control_msg() fills.
This sounds like a violation of the DMA rules. A buffer passed to usb_control_msg() must be allocated by kmalloc or equivalent, and it must not share a cache line with any other data values. Something in the middle of a larger struct is definitely not kosher. Alan Stern
