cxlflash: Fix AFU version access/storage and add check

The AFU version is stored as a non-terminated string of bytes within
a 64-bit little-endian register. Presently the value is read directly
(no MMIO accessor) and is stored in a buffer that is not big enough
to contain a NULL terminator. Additionally the version obtained is not
evaluated against a known value to prevent usage with unsupported AFUs.
All of these deficiencies can lead to a variety of problems.

To remedy, use the correct MMIO accessor to read the version value into
a null-terminated buffer and add a check to prevent an incompatible AFU
from being used with this driver.
Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Manoj N. Kumar <manoj@linux.vnet.ibm.com>
Reviewed-by: Brian King <brking@linux.vnet.ibm.com>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

drivers/scsi/cxlflash/common.h

@@ -179,7 +179,7 @@ struct afu {
 	u32 cmd_couts;		/* Number of command checkouts */
 	u32 internal_lun;	/* User-desired LUN mode for this AFU */
 
-	char version[8];
+	char version[16];
 	u64 interface_version;
 
 	struct cxlflash_cfg *parent; /* Pointer back to parent cxlflash_cfg */

drivers/scsi/cxlflash/main.c

@@ -1751,14 +1751,20 @@ static int init_afu(struct cxlflash_cfg *cfg)
 		goto err1;
 	}
 
-	/* don't byte reverse on reading afu_version, else the string form */
-	/*     will be backwards */
-	reg = afu->afu_map->global.regs.afu_version;
-	memcpy(afu->version, &reg, 8);
+	/* No byte reverse on reading afu_version or string will be backwards */
+	reg = readq(&afu->afu_map->global.regs.afu_version);
+	memcpy(afu->version, &reg, sizeof(reg));
 	afu->interface_version =
 	    readq_be(&afu->afu_map->global.regs.interface_version);
-	pr_debug("%s: afu version %s, interface version 0x%llX\n",
-		 __func__, afu->version, afu->interface_version);
+	if ((afu->interface_version + 1) == 0) {
+		pr_err("Back level AFU, please upgrade. AFU version %s "
+		       "interface version 0x%llx\n", afu->version,
+		       afu->interface_version);
+		rc = -EINVAL;
+		goto err1;
+	} else
+		pr_debug("%s: afu version %s, interface version 0x%llX\n",
+			 __func__, afu->version, afu->interface_version);
 
 	rc = start_afu(cfg);
 	if (rc) {

drivers/scsi/cxlflash/sislite.h

@@ -340,7 +340,7 @@ struct sisl_global_regs {
 #define SISL_AFUCONF_MBOX_CLR_READ     0x0010ULL
 	__be64 afu_config;
 	__be64 rsvd[0xf8];
-	__be64 afu_version;
+	__le64 afu_version;
 	__be64 interface_version;
 };