linux-kernel - [PATCH 5.4 103/147] usb: usbfs: correct kernel->user page attribute mismatch

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Date:   Mon, 18 May 2020 19:37:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jeremy Linton <jeremy.linton@....com>
Subject: [PATCH 5.4 103/147] usb: usbfs: correct kernel->user page attribute mismatch

From: Jeremy Linton <jeremy.linton@....com>

commit 2bef9aed6f0e22391c8d4570749b1acc9bc3981e upstream.

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@....com>
Cc: stable <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/20200504201348.1183246-1-jeremy.linton@arm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/usb/core/devio.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -217,6 +217,7 @@ static int usbdev_mmap(struct file *file
 {
 	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
 	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;
 	}