Commit 2bef9aed authored May 04, 2020 by Jeremy Linton Committed by Greg Kroah-Hartman May 05, 2020

usb: usbfs: correct kernel->user page attribute mismatch

On some architectures (e.g. arm64) requests for
IO coherent memory may use non-cachable attributes if
the relevant device isn't cache coherent. If these
pages are then remapped into userspace as cacheable,
they may not be coherent with the non-cacheable mappings.

In particular this happens with libusb, when it attempts
to create zero-copy buffers for use by rtl-sdr
(https://github.com/osmocom/rtl-sdr/

). On low end arm
devices with non-coherent USB ports, the application will
be unexpectedly killed, while continuing to work fine on
arm machines with coherent USB controllers.

This bug has been discovered/reported a few times over
the last few years. In the case of rtl-sdr a compile time
option to enable/disable zero copy was implemented to
work around it.

Rather than relaying on application specific workarounds,
dma_mmap_coherent() can be used instead of remap_pfn_range().
The page cache/etc attributes will then be correctly set in
userspace to match the kernel mapping.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200504201348.1183246-1-jeremy.linton@arm.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent e283f5e8

drivers/usb/core/devio.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -217,6 +217,7 @@ static int usbdev_mmap(struct file file, struct vm_area_struct vma)
		{
		struct usb_memory *usbm = NULL;
		struct usb_dev_state *ps = file->private_data;
		struct usb_hcd *hcd = bus_to_hcd(ps->dev->bus);
		size_t size = vma->vm_end - vma->vm_start;
		void *mem;
		unsigned long flags;
		@@ -250,9 +251,7 @@ static int usbdev_mmap(struct file file, struct vm_area_struct vma)
		usbm->vma_use_count = 1;
		INIT_LIST_HEAD(&usbm->memlist);

		if (remap_pfn_range(vma, vma->vm_start,
		virt_to_phys(usbm->mem) >> PAGE_SHIFT,
		size, vma->vm_page_prot) < 0) {
		if (dma_mmap_coherent(hcd->self.sysdev, vma, mem, dma_handle, size)) {
		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
		return -EAGAIN;
		}

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