[PATCH 1/2] HID: intel-thc-hid: intel-quickspi: size the input buffer for the DMA

[HyeongJun An <sammiee5311@gmail.com>]

quickspi_alloc_report_buf() sizes input_buf from max_input_len, but the
RXDMA2 channel it feeds is programmed with ALIGN(max_input_len, SZ_4K):
quickspi_dma_init() passes the raw value and dma_set_max_packet_size()
rounds it up.  setup_dma_buffers() maps that rounded size and
read_dma_buffer() bounds the message against it, so a controller
reporting max_input_len 64 and rep_desc_len 600 gets a 600 byte buffer
behind a 4096 byte DMA.  thc_rxdma_read() has no capacity argument, so
nothing downstream can catch it.

The intel-quicki2c sibling floors its input buffer at SZ_4K for this
reason, with the comment "give default 4K buffer to avoid DMA buffer
overrun".  Round up the same way the DMA does.

Fixes: 4138f21115ae ("HID: intel-thc-hid: intel-quickspi: Complete THC QuickSPI driver")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
---
 drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c b/drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c
index 89226f5ce45e..9ef33574c202 100644
--- a/drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c
+++ b/drivers/hid/intel-thc-hid/intel-quickspi/pci-quickspi.c
@@ -9,6 +9,7 @@
 #include <linux/interrupt.h>
 #include <linux/irqreturn.h>
 #include <linux/pci.h>
+#include <linux/sizes.h>
 #include <linux/pm_runtime.h>
 
 #include <linux/gpio/consumer.h>
@@ -549,8 +550,12 @@ static int quickspi_alloc_report_buf(struct quickspi_device *qsdev)
 	if (!qsdev->report_descriptor)
 		return -ENOMEM;
 
-	max_input_len = max(le16_to_cpu(qsdev->dev_desc.rep_desc_len),
-			    le16_to_cpu(qsdev->dev_desc.max_input_len));
+	/*
+	 * thc_dma_set_max_packet_sizes() rounds the RXDMA2 packet size up to
+	 * 4K, so the DMA can hand back more than max_input_len bytes.
+	 */
+	max_input_len = max_t(size_t, le16_to_cpu(qsdev->dev_desc.rep_desc_len),
+			      ALIGN(le16_to_cpu(qsdev->dev_desc.max_input_len), SZ_4K));
 
 	qsdev->input_buf = devm_kzalloc(qsdev->dev, max_input_len, GFP_KERNEL);
 	if (!qsdev->input_buf)
-- 
2.43.0