Subject: [PATCH v4 3/5] firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation

From: Mostafa Saleh <[email-masked]>
Date: Wed, 20 May 2026 20:49:46 +0000

From: Sebastian Ene <[email-masked]>

Use the descriptor's `ep_mem_offset` to calculate the start of the endpoint
memory access array and to comply with the FF-A spec instead of defaulting
to `sizeof(struct ffa_mem_region)`.
This requires moving `ffa_mem_region_additional_setup()` earlier in the setup
flow.
Also, add sanity checks to ensure the calculated descriptor offsets do not
exceed `max_fragsize`.

Signed-off-by: Sebastian Ene <[email-masked]>
Signed-off-by: Mostafa Saleh <[email-masked]>
---
 drivers/firmware/arm_ffa/driver.c | 16 +++++++++++-----
 include/linux/arm_ffa.h           |  2 +-
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index b700b2e93e72..8573a7a6556e 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -685,19 +685,26 @@ ffa_setup_and_transmit(u32 func_id, void *buffer, u32 max_fragsize,
 	struct ffa_composite_mem_region *composite;
 	struct ffa_mem_region_addr_range *constituents;
 	struct ffa_mem_region_attributes *ep_mem_access;
-	u32 idx, frag_len, length, buf_sz = 0, num_entries = sg_nents(args->sg);
+	u32 idx, frag_len, length, buf_sz = 0, num_entries = sg_nents(args->sg), ep_offset;
+	u32 emad_size = ffa_emad_size_get(drv_info->version);
 
 	mem_region->tag = args->tag;
 	mem_region->flags = args->flags;
 	mem_region->sender_id = drv_info->vm_id;
 	mem_region->attributes = ffa_memory_attributes_get(func_id);
+
+	ffa_mem_region_additional_setup(drv_info->version, mem_region);
 	composite_offset = ffa_mem_desc_offset(buffer, args->nattrs,
 					       drv_info->version);
+	if (composite_offset + sizeof(*composite) > max_fragsize)
+		return -ENXIO;
 
 	for (idx = 0; idx < args->nattrs; idx++) {
-		ep_mem_access = buffer +
-			ffa_mem_desc_offset(buffer, idx, drv_info->version);
-		memset(ep_mem_access, 0, ffa_emad_size_get(drv_info->version));
+		ep_offset = ffa_mem_desc_offset(buffer, idx, drv_info->version);
+		if (ep_offset + emad_size > max_fragsize)
+			return -ENXIO;
+		ep_mem_access = buffer + ep_offset;
+		memset(ep_mem_access, 0, emad_size);
 		ep_mem_access->receiver = args->attrs[idx].receiver;
 		ep_mem_access->attrs = args->attrs[idx].attrs;
 		ep_mem_access->composite_off = composite_offset;
@@ -707,7 +714,6 @@ ffa_setup_and_transmit(u32 func_id, void *buffer, u32 max_fragsize,
 	}
 	mem_region->handle = 0;
 	mem_region->ep_count = args->nattrs;
-	ffa_mem_region_additional_setup(drv_info->version, mem_region);
 
 	composite = buffer + composite_offset;
 	composite->total_pg_cnt = ffa_get_num_pages_sg(args->sg);
diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
index 81e603839c4a..62d67dae8b70 100644
--- a/include/linux/arm_ffa.h
+++ b/include/linux/arm_ffa.h
@@ -445,7 +445,7 @@ ffa_mem_desc_offset(struct ffa_mem_region *buf, int count, u32 ffa_version)
 	if (!FFA_MEM_REGION_HAS_EP_MEM_OFFSET(ffa_version))
 		offset += offsetof(struct ffa_mem_region, ep_mem_offset);
 	else
-		offset += sizeof(struct ffa_mem_region);
+		offset += buf->ep_mem_offset;
 
 	return offset;
 }
-- 
2.54.0.669.g59709faab0-goog