[PATCH 2/2] s390/dasd: enforce dma_alignment to ensure proper buffer validation

Stefan Haberland
2025-09-25T15:47:17Z

From: Jaehoon Kim <jhkim@linux.ibm.com>

The block layer validates buffer alignment using the device's
dma_alignment value. If dma_alignment is smaller than
logical_block_size(bp_block) -1, misaligned buffer incorrectly pass
validation and propagate to the lower-level driver.

This patch adjusts dma_alignment to be at least logical_block_size -1,
ensuring that misalignment buffers are properly rejected at the block
layer and do not reach the DASD driver unnecessarily.

Fixes: 2a07bb64d801 ("s390/dasd: Remove DMA alignment")
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Cc: stable@vger.kernel.org #6.11+
Signed-off-by: Jaehoon Kim <jhkim@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
---
drivers/s390/block/dasd.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index 6224ba412623..417a2dcf1587 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -334,6 +334,11 @@ static int dasd_state_basic_to_ready(struct dasd_device *device)
lim.max_dev_sectors = device->discipline->max_sectors(block);
lim.max_hw_sectors = lim.max_dev_sectors;
lim.logical_block_size = block->bp_block;
+ /*
+ * Adjust dma_alignment to match block_size - 1
+ * to ensure proper buffer alignment checks in the block layer.
+ */
+ lim.dma_alignment = lim.logical_block_size - 1;

if (device->discipline->has_discard) {
unsigned int max_bytes;
--
2.48.1