[PATCH] drm/panthor: snapshot firmware interface counts before loops

[Osama Abdelkader <osama.abdelkader@gmail.com>]

The firmware exposes the global group count and per-group stream count in
the shared control interface. These values are validated before being used
as loop bounds, but the memory is shared with the MCU firmware and can be
changed after validation.

Read each count once with READ_ONCE() and use the validated snapshot as the
loop bound. This keeps the loop bounds consistent with the validation and
prevents the compiler from reloading a firmware-controlled count during
iteration.

Fixes: 2718d91816ee ("drm/panthor: Add the FW logical block")
Cc: stable@vger.kernel.org
Signed-off-by: Osama Abdelkader <osama.abdelkader@gmail.com>
---
 drivers/gpu/drm/panthor/panthor_fw.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
index e2fcbd639c3c..6e6da98d795e 100644
--- a/drivers/gpu/drm/panthor/panthor_fw.c
+++ b/drivers/gpu/drm/panthor/panthor_fw.c
@@ -959,6 +959,7 @@ static int panthor_init_csg_iface(struct panthor_device *ptdev,
 	u64 shared_section_sz = panthor_kernel_bo_size(ptdev->fw->shared_section->mem);
 	u64 iface_offset = CSF_GROUP_CONTROL_OFFSET +
 			   ((u64)csg_idx * glb_iface->control->group_stride);
+	u32 stream_num;
 	unsigned int i;
 
 	if (iface_offset > shared_section_sz ||
@@ -972,8 +973,8 @@ static int panthor_init_csg_iface(struct panthor_device *ptdev,
 	csg_iface->output = iface_fw_to_cpu_addr(ptdev, csg_iface->control->output_va,
 						 sizeof(*csg_iface->output));
 
-	if (csg_iface->control->stream_num < MIN_CS_PER_CSG ||
-	    csg_iface->control->stream_num > MAX_CS_PER_CSG)
+	stream_num = READ_ONCE(csg_iface->control->stream_num);
+	if (stream_num < MIN_CS_PER_CSG || stream_num > MAX_CS_PER_CSG)
 		return -EINVAL;
 
 	if (!csg_iface->input || !csg_iface->output) {
@@ -990,7 +991,7 @@ static int panthor_init_csg_iface(struct panthor_device *ptdev,
 		}
 	}
 
-	for (i = 0; i < csg_iface->control->stream_num; i++) {
+	for (i = 0; i < stream_num; i++) {
 		int ret = panthor_init_cs_iface(ptdev, csg_idx, i);
 
 		if (ret)
@@ -1015,6 +1016,7 @@ static int panthor_fw_init_ifaces(struct panthor_device *ptdev)
 {
 	struct panthor_fw_global_iface *glb_iface = &ptdev->fw->iface.global;
 	u64 shared_section_sz = panthor_kernel_bo_size(ptdev->fw->shared_section->mem);
+	u32 group_num;
 	unsigned int i;
 
 	if (!ptdev->fw->shared_section->mem->kmap)
@@ -1034,17 +1036,17 @@ static int panthor_fw_init_ifaces(struct panthor_device *ptdev)
 		return -EINVAL;
 	}
 
-	if (glb_iface->control->group_num > MAX_CSGS ||
-	    glb_iface->control->group_num < MIN_CSGS) {
+	group_num = READ_ONCE(glb_iface->control->group_num);
+	if (group_num > MAX_CSGS || group_num < MIN_CSGS) {
 		drm_err(&ptdev->base, "Invalid number of control groups");
 		return -EINVAL;
 	}
 
-	for (i = 0; i < glb_iface->control->group_num; i++) {
+	for (i = 0; i < group_num; i++) {
 		int ret = panthor_init_csg_iface(ptdev, i);
 
 		if (ret)
 			return ret;
 	}
 
 	drm_info(&ptdev->base, "CSF FW using interface v%d.%d.%d, Features %#x Instrumentation features %#x",
-- 
2.43.0