cxl_get_feature() and cxl_set_feature() build each mailbox command's
offset from the starting offset plus the amount of data already
transferred, then store it in a 16-bit field. An user-controlled fwctl
offset and transfer size can exceed the feature extent, allowing a later
offset to be truncated by cpu_to_le16() and target the wrong feature
data.

Reject requests whose transfer size exceeeds the remaining 16-bit
feature range. Express the check as "size > U16_MAX - offset" so the
validation itself can't wrap on 32-bit systems.

Change cxl_get_feature() to return ssize_t so invalid input and mailbox
failures are reported as negative errno rather than being conflated with
a zero-byte result. Update the EDAC callers to handle negative results.
Keep fwctl behvaior unchanged by translating helper failures to the same
header-only RPC response carrying the CXL mailbox return code.

Fixes: 5e5ac21f629d ("cxl/mbox: Add GET_FEATURE mailbox command")
Fixes: 14d502cc2718 ("cxl/mbox: Add SET_FEATURE mailbox command")
Signed-off-by: Richard Cheng <icheng@nvidia.com>
---
Changelog:

v2->v3:
    - Change cxl_get_feature() to return ssize_t and report negative
      errno.
    - Update all EDAC callers for the signed return contract.
    - Preserve the existing fwctl RPC response behavior on helper
      failure.

v1->v2:
    - refactor the guard to "size > U16_MAX - offset", the addition is
      performed in size_t, so on 32-bit arch a large user-supplied size
wrpas the  sum and bypasses the check. The substraction form can't
misbehave since offset is a u16, making U16_MAX - offset always
well-defined.
---
 drivers/cxl/core/core.h     |  2 +-
 drivers/cxl/core/edac.c     | 20 +++++++++++++++-----
 drivers/cxl/core/features.c | 22 +++++++++++++++-------
 3 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
index 07555ae63859..09dd1c1722dd 100644
--- a/drivers/cxl/core/core.h
+++ b/drivers/cxl/core/core.h
@@ -218,7 +218,7 @@ int cxl_port_get_possible_dports(struct cxl_port *port);
 #ifdef CONFIG_CXL_FEATURES
 struct cxl_feat_entry *
 cxl_feature_info(struct cxl_features_state *cxlfs, const uuid_t *uuid);
-size_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
+ssize_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
 		       enum cxl_get_feat_selection selection,
 		       void *feat_out, size_t feat_out_size, u16 offset,
 		       u16 *return_code);
diff --git a/drivers/cxl/core/edac.c b/drivers/cxl/core/edac.c
index b321971fef58..f1df4b5cfe5b 100644
--- a/drivers/cxl/core/edac.c
+++ b/drivers/cxl/core/edac.c
@@ -78,7 +78,7 @@ static int cxl_mem_scrub_get_attrbs(struct cxl_mailbox *cxl_mbox, u8 *cap,
 				    u16 *cycle, u8 *flags, u8 *min_cycle)
 {
 	size_t rd_data_size = sizeof(struct cxl_scrub_rd_attrbs);
-	size_t data_size;
+	ssize_t data_size;
 	struct cxl_scrub_rd_attrbs *rd_attrbs __free(kfree) =
 		kzalloc(rd_data_size, GFP_KERNEL);
 	if (!rd_attrbs)
@@ -87,6 +87,8 @@ static int cxl_mem_scrub_get_attrbs(struct cxl_mailbox *cxl_mbox, u8 *cap,
 	data_size = cxl_get_feature(cxl_mbox, &CXL_FEAT_PATROL_SCRUB_UUID,
 				    CXL_GET_FEAT_SEL_CURRENT_VALUE, rd_attrbs,
 				    rd_data_size, 0, NULL);
+	if (data_size < 0)
+		return data_size;
 	if (!data_size)
 		return -EIO;
 
@@ -551,7 +553,7 @@ static int cxl_mem_ecs_get_attrbs(struct device *dev,
 	struct cxl_mailbox *cxl_mbox = &cxlmd->cxlds->cxl_mbox;
 	struct cxl_ecs_fru_rd_attrbs *fru_rd_attrbs;
 	size_t rd_data_size;
-	size_t data_size;
+	ssize_t data_size;
 
 	rd_data_size = cxl_ecs_ctx->get_feat_size;
 
@@ -563,6 +565,8 @@ static int cxl_mem_ecs_get_attrbs(struct device *dev,
 	data_size = cxl_get_feature(cxl_mbox, &CXL_FEAT_ECS_UUID,
 				    CXL_GET_FEAT_SEL_CURRENT_VALUE, rd_attrbs,
 				    rd_data_size, 0, NULL);
+	if (data_size < 0)
+		return data_size;
 	if (!data_size)
 		return -EIO;
 
@@ -583,7 +587,7 @@ static int cxl_mem_ecs_set_attrbs(struct device *dev,
 	struct cxl_ecs_fru_wr_attrbs *fru_wr_attrbs;
 	size_t rd_data_size, wr_data_size;
 	u16 num_media_frus, count;
-	size_t data_size;
+	ssize_t data_size;
 
 	num_media_frus = cxl_ecs_ctx->num_media_frus;
 	rd_data_size = cxl_ecs_ctx->get_feat_size;
@@ -596,6 +600,8 @@ static int cxl_mem_ecs_set_attrbs(struct device *dev,
 	data_size = cxl_get_feature(cxl_mbox, &CXL_FEAT_ECS_UUID,
 				    CXL_GET_FEAT_SEL_CURRENT_VALUE, rd_attrbs,
 				    rd_data_size, 0, NULL);
+	if (data_size < 0)
+		return data_size;
 	if (!data_size)
 		return -EIO;
 
@@ -1264,7 +1270,7 @@ cxl_mem_sparing_get_attrbs(struct cxl_mem_sparing_context *cxl_sparing_ctx)
 	struct cxl_memdev *cxlmd = cxl_sparing_ctx->cxlmd;
 	struct cxl_mailbox *cxl_mbox = &cxlmd->cxlds->cxl_mbox;
 	u16 restriction_flags;
-	size_t data_size;
+	ssize_t data_size;
 	u16 return_code;
 	struct cxl_memdev_sparing_rd_attrbs *rd_attrbs __free(kfree) =
 		kzalloc(rd_data_size, GFP_KERNEL);
@@ -1274,6 +1280,8 @@ cxl_mem_sparing_get_attrbs(struct cxl_mem_sparing_context *cxl_sparing_ctx)
 	data_size = cxl_get_feature(cxl_mbox, &cxl_sparing_ctx->repair_uuid,
 				    CXL_GET_FEAT_SEL_CURRENT_VALUE, rd_attrbs,
 				    rd_data_size, 0, &return_code);
+	if (data_size < 0)
+		return data_size;
 	if (!data_size)
 		return -EIO;
 
@@ -1750,7 +1758,7 @@ static int cxl_mem_ppr_get_attrbs(struct cxl_ppr_context *cxl_ppr_ctx)
 	struct cxl_memdev *cxlmd = cxl_ppr_ctx->cxlmd;
 	struct cxl_mailbox *cxl_mbox = &cxlmd->cxlds->cxl_mbox;
 	u16 restriction_flags;
-	size_t data_size;
+	ssize_t data_size;
 	u16 return_code;
 
 	struct cxl_memdev_ppr_rd_attrbs *rd_attrbs __free(kfree) =
@@ -1761,6 +1769,8 @@ static int cxl_mem_ppr_get_attrbs(struct cxl_ppr_context *cxl_ppr_ctx)
 	data_size = cxl_get_feature(cxl_mbox, &cxl_ppr_ctx->repair_uuid,
 				    CXL_GET_FEAT_SEL_CURRENT_VALUE, rd_attrbs,
 				    rd_data_size, 0, &return_code);
+	if (data_size < 0)
+		return data_size;
 	if (!data_size)
 		return -EIO;
 
diff --git a/drivers/cxl/core/features.c b/drivers/cxl/core/features.c
index 85185af46b72..aaa408445fd4 100644
--- a/drivers/cxl/core/features.c
+++ b/drivers/cxl/core/features.c
@@ -220,7 +220,7 @@ int devm_cxl_setup_features(struct cxl_dev_state *cxlds)
 }
 EXPORT_SYMBOL_NS_GPL(devm_cxl_setup_features, "CXL");
 
-size_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
+ssize_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
 		       enum cxl_get_feat_selection selection,
 		       void *feat_out, size_t feat_out_size, u16 offset,
 		       u16 *return_code)
@@ -235,7 +235,10 @@ size_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
 		*return_code = CXL_MBOX_CMD_RC_INPUT;
 
 	if (!feat_out || !feat_out_size)
-		return 0;
+		return -EINVAL;
+
+	if (feat_out_size > U16_MAX - offset)
+		return -EINVAL;
 
 	size_out = min(feat_out_size, cxl_mbox->payload_size);
 	uuid_copy(&pi.uuid, feat_uuid);
@@ -258,7 +261,7 @@ size_t cxl_get_feature(struct cxl_mailbox *cxl_mbox, const uuid_t *feat_uuid,
 		if (rc < 0 || !mbox_cmd.size_out) {
 			if (return_code)
 				*return_code = mbox_cmd.return_code;
-			return 0;
+			return rc < 0 ? rc : -EIO;
 		}
 		data_rcvd_size += mbox_cmd.size_out;
 	} while (data_rcvd_size < feat_out_size);
@@ -287,6 +290,9 @@ int cxl_set_feature(struct cxl_mailbox *cxl_mbox,
 	if (return_code)
 		*return_code = CXL_MBOX_CMD_RC_INPUT;
 
+	if (feat_data_size > U16_MAX - offset)
+		return -EINVAL;
+
 	struct cxl_mbox_set_feat_in *pi __free(kfree) =
 			kzalloc(cxl_mbox->payload_size, GFP_KERNEL);
 	if (!pi)
@@ -460,6 +466,7 @@ static void *cxlctl_get_feature(struct cxl_features_state *cxlfs,
 	const struct cxl_mbox_get_feat_in *feat_in;
 	u16 offset, count, return_code;
 	size_t out_size = *out_len;
+	ssize_t data_size;
 
 	if (rpc_in->op_size != sizeof(*feat_in))
 		return ERR_PTR(-EINVAL);
@@ -476,16 +483,17 @@ static void *cxlctl_get_feature(struct cxl_features_state *cxlfs,
 	if (!rpc_out)
 		return ERR_PTR(-ENOMEM);
 
-	out_size = cxl_get_feature(cxl_mbox, &feat_in->uuid,
-				   feat_in->selection, rpc_out->payload,
-				   count, offset, &return_code);
+	data_size = cxl_get_feature(cxl_mbox, &feat_in->uuid,
+				    feat_in->selection, rpc_out->payload,
+				    count, offset, &return_code);
 	*out_len = sizeof(struct fwctl_rpc_cxl_out);
-	if (!out_size) {
+	if (data_size <= 0) {
 		rpc_out->size = 0;
 		rpc_out->retval = return_code;
 		return no_free_ptr(rpc_out);
 	}
 
+	out_size = data_size;
 	rpc_out->size = out_size;
 	rpc_out->retval = CXL_MBOX_CMD_RC_SUCCESS;
 	*out_len += out_size;
-- 
2.43.0