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usb: ensure RX buffers are a multiple of the packet size

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When performing an OUT transfer which is not a multiple of the
max packet size, the last packet of the OUT transfer should be
a short packet. However, there's no guarantee the host sends
the expected amount of data in the final packet.

The DWC2 USB controller handles this case by accepting any size
packet and copying it out to memory. So if the packet is bigger
than expected, it'll overrun the caller's buffer and Bad Things
will happen.

The USB 2.0 spec seems to endorse this behavior. Section 8.5.1
says "an ACK handshake indicates the endpoint has space for a
wMaxPacketSize data payload." So it is possible that other USB
controllers share the DWC2's behavior.

The simplest solution is to force all USB RX buffers to be big
enough to hold the transfer size, rounded up to a multiple of
the max packet size. For example, a transfer of 700 bytes would
require a 1024-byte buffer if the MPS = 512 bytes.

Change-Id: Ibb84d2b2d53aec8800a3a7c2449f7a17480acbcf
This commit is contained in:
Aidan MacDonald 2021-09-24 22:41:07 +01:00
parent a665c1faad
commit 24294bda15
3 changed files with 25 additions and 12 deletions
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3
firmware/usbstack/usb_hid.c
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@ -666,8 +666,7 @@ void usb_hid_transfer_complete(int ep, int dir, int status, int length)
* to the DAP using the host's custom driver */
static int usb_hid_set_report(struct usb_ctrlrequest *req, void *reqdata)
{
static unsigned char buf[SET_REPORT_BUF_LEN] USB_DEVBSS_ATTR
__attribute__((aligned(32)));
static unsigned char buf[64] USB_DEVBSS_ATTR __attribute__((aligned(32)));
int length;
if ((req->wValue >> 8) != REPORT_TYPE_OUTPUT)