cxl/mem: Add a "RAW" send command

The CXL memory device send interface will have a number of supported
commands. The raw command is not such a command. Raw commands allow
userspace to send a specified opcode to the underlying hardware and
bypass all driver checks on the command. The primary use for this
command is to [begrudgingly] allow undocumented vendor specific hardware
commands.

While not the main motivation, it also allows prototyping new hardware
commands without a driver patch and rebuild.

While this all sounds very powerful it comes with a couple of caveats:
1. Bug reports using raw commands will not get the same level of
attention as bug reports using supported commands (via taint).
2. Supported commands will be rejected by the RAW command.

With this comes new debugfs knob to allow full access to your toes with
your weapon of choice.

Signed-off-by: Ben Widawsky <[e-mail]>
Reviewed-by: Dan Williams <[e-mail]> (v2)
Reviewed-by: Jonathan Cameron <[e-mail]>
Cc: Ariel Sibley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

drivers/cxl/Kconfig

···
 	  Chapter 2.3 Type 3 CXL Device in the CXL 2.0 specification.
 
 	  If unsure say 'm'.
+
+config CXL_MEM_RAW_COMMANDS
+	bool "RAW Command Interface for Memory Devices"
+	depends on CXL_MEM
+	help
+	  Enable CXL RAW command interface.
+
+	  The CXL driver ioctl interface may assign a kernel ioctl command
+	  number for each specification defined opcode. At any given point in
+	  time the number of opcodes that the specification defines and a device
+	  may implement may exceed the kernel's set of associated ioctl function
+	  numbers. The mismatch is either by omission, specification is too new,
+	  or by design. When prototyping new hardware, or developing / debugging
+	  the driver it is useful to be able to submit any possible command to
+	  the hardware, even commands that may crash the kernel due to their
+	  potential impact to memory currently in use by the kernel.
+
+	  If developing CXL hardware or the driver say Y, otherwise say N.
 endif

drivers/cxl/mem.c

···
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2020 Intel Corporation. All rights reserved. */
 #include <uapi/linux/cxl_mem.h>
+#include <linux/security.h>
+#include <linux/debugfs.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/cdev.h>
···
 
 enum opcode {
 	CXL_MBOX_OP_INVALID		= 0x0000,
+	CXL_MBOX_OP_RAW			= CXL_MBOX_OP_INVALID,
+	CXL_MBOX_OP_ACTIVATE_FW		= 0x0202,
 	CXL_MBOX_OP_IDENTIFY		= 0x4000,
+	CXL_MBOX_OP_SET_PARTITION_INFO	= 0x4101,
+	CXL_MBOX_OP_SET_LSA		= 0x4103,
+	CXL_MBOX_OP_SET_SHUTDOWN_STATE	= 0x4204,
+	CXL_MBOX_OP_SCAN_MEDIA		= 0x4304,
+	CXL_MBOX_OP_GET_SCAN_MEDIA	= 0x4305,
 	CXL_MBOX_OP_MAX			= 0x10000
 };
 
···
 
 static int cxl_mem_major;
 static DEFINE_IDA(cxl_memdev_ida);
+static struct dentry *cxl_debugfs;
+static bool cxl_raw_allow_all;
 
 /**
  * struct cxl_mem_command - Driver representation of a memory device command
···
  */
 static struct cxl_mem_command mem_commands[] = {
 	CXL_CMD(IDENTIFY, 0, 0x43),
+#ifdef CONFIG_CXL_MEM_RAW_COMMANDS
+	CXL_CMD(RAW, ~0, ~0),
+#endif
+};
+
+/*
+ * Commands that RAW doesn't permit. The rationale for each:
+ *
+ * CXL_MBOX_OP_ACTIVATE_FW: Firmware activation requires adjustment /
+ * coordination of transaction timeout values at the root bridge level.
+ *
+ * CXL_MBOX_OP_SET_PARTITION_INFO: The device memory map may change live
+ * and needs to be coordinated with HDM updates.
+ *
+ * CXL_MBOX_OP_SET_LSA: The label storage area may be cached by the
+ * driver and any writes from userspace invalidates those contents.
+ *
+ * CXL_MBOX_OP_SET_SHUTDOWN_STATE: Set shutdown state assumes no writes
+ * to the device after it is marked clean, userspace can not make that
+ * assertion.
+ *
+ * CXL_MBOX_OP_[GET_]SCAN_MEDIA: The kernel provides a native error list that
+ * is kept up to date with patrol notifications and error management.
+ */
+static u16 cxl_disabled_raw_commands[] = {
+	CXL_MBOX_OP_ACTIVATE_FW,
+	CXL_MBOX_OP_SET_PARTITION_INFO,
+	CXL_MBOX_OP_SET_LSA,
+	CXL_MBOX_OP_SET_SHUTDOWN_STATE,
+	CXL_MBOX_OP_SCAN_MEDIA,
+	CXL_MBOX_OP_GET_SCAN_MEDIA,
+};
+
+/*
+ * Command sets that RAW doesn't permit. All opcodes in this set are
+ * disabled because they pass plain text security payloads over the
+ * user/kernel boundary. This functionality is intended to be wrapped
+ * behind the keys ABI which allows for encrypted payloads in the UAPI
+ */
+static u8 security_command_sets[] = {
+	0x44, /* Sanitize */
+	0x45, /* Persistent Memory Data-at-rest Security */
+	0x46, /* Security Passthrough */
 };
 
 #define cxl_for_each_cmd(cmd)                                                  \
···
 	dev_dbg(&cxlm->pdev->dev, "Doorbell wait took %dms",
 		jiffies_to_msecs(end) - jiffies_to_msecs(start));
 	return 0;
+}
+
+static bool cxl_is_security_command(u16 opcode)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(security_command_sets); i++)
+		if (security_command_sets[i] == (opcode >> 8))
+			return true;
+	return false;
 }
 
 static void cxl_mem_mbox_timeout(struct cxl_mem *cxlm,
···
 		cxl_command_names[cmd->info.id].name, mbox_cmd.opcode,
 		cmd->info.size_in);
 
+	dev_WARN_ONCE(dev, cmd->info.id == CXL_MEM_COMMAND_ID_RAW,
+		      "raw command path used\n");
+
 	rc = __cxl_mem_mbox_send_cmd(cxlm, &mbox_cmd);
 	cxl_mem_mbox_put(cxlm);
 	if (rc)
···
 	return rc;
 }
 
+static bool cxl_mem_raw_command_allowed(u16 opcode)
+{
+	int i;
+
+	if (!IS_ENABLED(CONFIG_CXL_MEM_RAW_COMMANDS))
+		return false;
+
+	if (security_locked_down(LOCKDOWN_NONE))
+		return false;
+
+	if (cxl_raw_allow_all)
+		return true;
+
+	if (cxl_is_security_command(opcode))
+		return false;
+
+	for (i = 0; i < ARRAY_SIZE(cxl_disabled_raw_commands); i++)
+		if (cxl_disabled_raw_commands[i] == opcode)
+			return false;
+
+	return true;
+}
+
 /**
  * cxl_validate_cmd_from_user() - Check fields for CXL_MEM_SEND_COMMAND.
  * @cxlm: &struct cxl_mem device whose mailbox will be used.
···
  *  * %-ENOTTY	- Invalid command specified.
  *  * %-EINVAL	- Reserved fields or invalid values were used.
  *  * %-ENOMEM	- Input or output buffer wasn't sized properly.
+ *  * %-EPERM	- Attempted to use a protected command.
  *
  * The result of this command is a fully validated command in @out_cmd that is
  * safe to send to the hardware.
···
 	 */
 	if (send_cmd->in.size > cxlm->payload_size)
 		return -EINVAL;
+
+	/*
+	 * Checks are bypassed for raw commands but a WARN/taint will occur
+	 * later in the callchain
+	 */
+	if (send_cmd->id == CXL_MEM_COMMAND_ID_RAW) {
+		const struct cxl_mem_command temp = {
+			.info = {
+				.id = CXL_MEM_COMMAND_ID_RAW,
+				.flags = 0,
+				.size_in = send_cmd->in.size,
+				.size_out = send_cmd->out.size,
+			},
+			.opcode = send_cmd->raw.opcode
+		};
+
+		if (send_cmd->raw.rsvd)
+			return -EINVAL;
+
+		/*
+		 * Unlike supported commands, the output size of RAW commands
+		 * gets passed along without further checking, so it must be
+		 * validated here.
+		 */
+		if (send_cmd->out.size > cxlm->payload_size)
+			return -EINVAL;
+
+		if (!cxl_mem_raw_command_allowed(send_cmd->raw.opcode))
+			return -EPERM;
+
+		memcpy(out_cmd, &temp, sizeof(temp));
+
+		return 0;
+	}
 
 	if (send_cmd->flags & ~CXL_MEM_COMMAND_FLAG_MASK)
 		return -EINVAL;
···
 
 static __init int cxl_mem_init(void)
 {
+	struct dentry *mbox_debugfs;
 	dev_t devt;
 	int rc;
 
···
 		return rc;
 	}
 
+	cxl_debugfs = debugfs_create_dir("cxl", NULL);
+	mbox_debugfs = debugfs_create_dir("mbox", cxl_debugfs);
+	debugfs_create_bool("raw_allow_all", 0600, mbox_debugfs,
+			    &cxl_raw_allow_all);
+
 	return 0;
 }
 
 static __exit void cxl_mem_exit(void)
 {
+	debugfs_remove_recursive(cxl_debugfs);
 	pci_unregister_driver(&cxl_mem_driver);
 	unregister_chrdev_region(MKDEV(cxl_mem_major, 0), CXL_MEM_MAX_DEVS);
 }

include/uapi/linux/cxl_mem.h

···
 #define CXL_CMDS                                                          \
 	___C(INVALID, "Invalid Command"),                                 \
 	___C(IDENTIFY, "Identify Command"),                               \
+	___C(RAW, "Raw device command"),                                  \
 	___C(MAX, "invalid / last command")
 
 #define ___C(a, b) CXL_MEM_COMMAND_ID_##a
···
  * @id: The command to send to the memory device. This must be one of the
  *	commands returned by the query command.
  * @flags: Flags for the command (input).
+ * @raw: Special fields for raw commands
+ * @raw.opcode: Opcode passed to hardware when using the RAW command.
+ * @raw.rsvd: Must be zero.
  * @rsvd: Must be zero.
  * @retval: Return value from the memory device (output).
  * @in: Parameters associated with input payload.
···
 struct cxl_send_command {
 	__u32 id;
 	__u32 flags;
-	__u32 rsvd;
+	union {
+		struct {
+			__u16 opcode;
+			__u16 rsvd;
+		} raw;
+		__u32 rsvd;
+	};
 	__u32 retval;
 
 	struct {