Since commit faa8e404ad8e ("spi: imx: support dynamic burst length for ECSPI DMA mode"), the driver allocates its private DMA TX/RX buffers with kzalloc(dma_len), where dma_len is only rounded up to 4 bytes, but maps, syncs and unmaps them with DMA_CACHE_ALIGNED_LEN(dma_len), i.e. rounded up to the cache line size. As a result, the DMA API operates on memory beyond the end of the allocation. This was observed on a custom i.MX8MP platform with an mcp251xfd CAN controller under heavy RPMSG load, as a series of refcount_t warnings triggered from rpmsg_recv_done() in virtio_rpmsg_bus: refcount_t: addition on 0; use-after-free. refcount_t: underflow; use-after-free. refcount_t: saturated; leaking memory. Leading finally to an "Unable to handle kernel paging request" oops. Reproducing this problem took between 30 minutes and roughly 30 hours under the same workload. Hardware watchpoints on the refcount of a struct rpmsg_endpoint showed it was overwritten from 2 to 1 by __pi_memcpy_generic() in the irq/155-spi2.0 thread. Additionally it was found that a "normal" rpmsg_recv_done() took 11µs +/-2µs from its kref_get to kref_put. In the error case the same sequence took about 215µs +/-10µs. Based on this, an LLM was used to identify the size mismatch fixed here. Allocate the buffers with DMA_CACHE_ALIGNED_LEN(dma_len) so they cover the full mapped length, and use the same length for dma_sync_single_for_cpu() to stay consistent with map and unmap. With this patch applied, the same workload ran for more than 200 hours without the problem reproducing. Assisted-by: LLM Fixes: faa8e404ad8e ("spi: imx: support dynamic burst length for ECSPI DMA mode") Cc: stable@vger.kernel.org Signed-off-by: Richard Leitner --- drivers/spi/spi-imx.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index 79a6c1a60b0a0..3851c50dbe314 100644 --- a/drivers/spi/spi-imx.c +++ b/drivers/spi/spi-imx.c @@ -1578,11 +1578,13 @@ static int spi_imx_dma_tx_data_handle(struct spi_imx_data *spi_imx, dma_data->dma_len = ALIGN(dma_data->data_len, BYTES_PER_32BITS_WORD); } - dma_data->dma_tx_buf = kzalloc(dma_data->dma_len, GFP_KERNEL); + dma_data->dma_tx_buf = kzalloc(DMA_CACHE_ALIGNED_LEN(dma_data->dma_len), + GFP_KERNEL); if (!dma_data->dma_tx_buf) return -ENOMEM; - dma_data->dma_rx_buf = kzalloc(dma_data->dma_len, GFP_KERNEL); + dma_data->dma_rx_buf = kzalloc(DMA_CACHE_ALIGNED_LEN(dma_data->dma_len), + GFP_KERNEL); if (!dma_data->dma_rx_buf) { kfree(dma_data->dma_tx_buf); return -ENOMEM; @@ -1920,7 +1922,8 @@ static int spi_imx_dma_package_transfer(struct spi_imx_data *spi_imx, /* Trim the DMA RX buffer and copy the actual data to rx_buf */ dma_sync_single_for_cpu(controller->dma_rx->device->dev, dma_data->dma_rx_addr, - dma_data->dma_len, DMA_FROM_DEVICE); + DMA_CACHE_ALIGNED_LEN(dma_data->dma_len), + DMA_FROM_DEVICE); spi_imx_dma_rx_data_handle(spi_imx, dma_data, transfer->rx_buf + spi_imx->rx_offset, word_delay); spi_imx->rx_offset += dma_data->data_len; --- base-commit: 62f482ff73bf3ae88b0c899115527752cf9cbf13 change-id: 20261015-fix-spi-imx-dma-1bab95ea4863 Best regards, -- Richard Leitner