scsi: mptctl: fix potential Spectre v1

karg->hdr.port is indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

drivers/message/fusion/mptctl.c:1360 mptctl_getiocinfo() warn: potential spectre issue 'ioc->pfacts' [r]

Fix this by sanitizing karg->hdr.port before indirectly using it to index ioc->pfacts

Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

---
Notice that the '1 + 1' thing is intentional for clarity purposes.

 drivers/message/fusion/mptctl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index 8d22d61..afc6979 100644
@@ -59,6 +59,7 @@
 
 #include <asm/io.h>
 #include <linux/uaccess.h>
+#include <linux/nospec.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>

@@ -1306,7 +1307,7 @@ mptctl_getiocinfo (unsigned long arg, unsigned int data_size)
 		kfree(karg);
 		return -EINVAL;
 	}
-	port = karg->hdr.port;
+	port = array_index_nospec(karg->hdr.port, 1 + 1);
 
 	karg->port = port;
 	pdev = (struct pci_dev *) ioc->pcidev;

2.7.4