cxl/mbox: Block immediate mode in SET_PARTITION_INFO command

User space may send the SET_PARTITION_INFO mailbox command using
the IOCTL interface. Inspect the input payload and fail if the
immediate flag is set.

This is the first instance of the driver inspecting an input payload
from user space. Assume there will be more such cases and implement
with an extensible helper.

In order for the kernel to react to an immediate partition change it
needs to assert that the change will not affect any active decode. At
a minimum this requires validating that the device is using HDM
decoders instead of the CXL DVSEC for decode, and that none of the
active HDM decoders are affected by the partition change. For now,
just fail until that support arrives.

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/241821186c363833980adbc389e2c547bc5a6395.1648687552.git.alison.schofield@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/mbox.c

@@ -218,6 +218,40 @@ static bool cxl_mem_raw_command_allowed(u16 opcode)
 	return true;
 }
 
+/**
+ * cxl_payload_from_user_allowed() - Check contents of in_payload.
+ * @opcode: The mailbox command opcode.
+ * @payload_in: Pointer to the input payload passed in from user space.
+ *
+ * Return:
+ *  * true	- payload_in passes check for @opcode.
+ *  * false	- payload_in contains invalid or unsupported values.
+ *
+ * The driver may inspect payload contents before sending a mailbox
+ * command from user space to the device. The intent is to reject
+ * commands with input payloads that are known to be unsafe. This
+ * check is not intended to replace the users careful selection of
+ * mailbox command parameters and makes no guarantee that the user
+ * command will succeed, nor that it is appropriate.
+ *
+ * The specific checks are determined by the opcode.
+ */
+static bool cxl_payload_from_user_allowed(u16 opcode, void *payload_in)
+{
+	switch (opcode) {
+	case CXL_MBOX_OP_SET_PARTITION_INFO: {
+		struct cxl_mbox_set_partition_info *pi = payload_in;
+
+		if (pi->flags && CXL_SET_PARTITION_IMMEDIATE_FLAG)
+			return false;
+		break;
+	}
+	default:
+		break;
+	}
+	return true;
+}
+
 static int cxl_mbox_cmd_ctor(struct cxl_mbox_cmd *mbox,
 			     struct cxl_dev_state *cxlds, u16 opcode,
 			     size_t in_size, size_t out_size, u64 in_payload)
@@ -232,6 +266,13 @@ static int cxl_mbox_cmd_ctor(struct cxl_mbox_cmd *mbox,
 						in_size);
 		if (!mbox->payload_in)
 			return PTR_ERR(mbox->payload_in);
+
+		if (!cxl_payload_from_user_allowed(opcode, mbox->payload_in)) {
+			dev_dbg(cxlds->dev, "%s: input payload not allowed\n",
+				cxl_mem_opcode_to_name(opcode));
+			kvfree(mbox->payload_in);
+			return -EBUSY;
+		}
 	}
 
 	/* Prepare to handle a full payload for variable sized output */

drivers/cxl/cxlmem.h

@@ -262,6 +262,13 @@ struct cxl_mbox_set_lsa {
 	u8 data[];
 } __packed;
 
+struct cxl_mbox_set_partition_info {
+	__le64 volatile_capacity;
+	u8 flags;
+} __packed;
+
+#define  CXL_SET_PARTITION_IMMEDIATE_FLAG	BIT(0)
+
 /**
  * struct cxl_mem_command - Driver representation of a memory device command
  * @info: Command information as it exists for the UAPI