[PATCH] coresight: ultrasoc-smb: Fix OOB write in smb_sync_perf_buffer()

[Junrui Luo]

When the SMB sink is used as a perf AUX sink, smb_update_buffer() calls
smb_sync_perf_buffer() to copy hardware trace data into the perf AUX ring
buffer pages. It derives pg_idx = head >> PAGE_SHIFT from @head, which is
handle->head, and indexes dst_pages[pg_idx]. The pg_idx %= nr_pages
normalization is only applied after the first loop iteration.

This leaves the initial page index underived from the buffer size, which
can result in an out-of-bounds write past dst_pages[] when head exceeds
the AUX buffer size.

Normalize head modulo the AUX buffer size before deriving the page index
and offset, mirroring tmc_etr_sync_perf_buffer().

Fixes: 06f5c2926aaa ("drivers/coresight: Add UltraSoc System Memory Buffer driver")
Reported-by: Yuhao Jiang <danisjiang at gmail.com>
Cc: stable at vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain at outlook.com>
---
 drivers/hwtracing/coresight/ultrasoc-smb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hwtracing/coresight/ultrasoc-smb.c b/drivers/hwtracing/coresight/ultrasoc-smb.c
index 5776f63468fa..20a950b9dd4f 100644
--- a/drivers/hwtracing/coresight/ultrasoc-smb.c
+++ b/drivers/hwtracing/coresight/ultrasoc-smb.c
@@ -337,6 +337,7 @@ static void smb_sync_perf_buffer(struct smb_drv_data *drvdata,
 	unsigned long to_copy;
 	long pg_idx, pg_offset;
 
+	head %= (unsigned long)buf->nr_pages << PAGE_SHIFT;
 	pg_idx = head >> PAGE_SHIFT;
 	pg_offset = head & (PAGE_SIZE - 1);
 

---
base-commit: e43ffb69e0438cddd72aaa30898b4dc446f664f8
change-id: 20260604-fixes-edc5369a8aca

Best regards,
-- 
Junrui Luo <moonafterrain at outlook.com>