From 46feb6b495f7628a6dbf36c4e6d80faf378372d4 Mon Sep 17 00:00:00 2001
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Thu, 16 Aug 2018 14:06:46 -0500
Subject: [PATCH] switchtec: Fix Spectre v1 vulnerability
Git-commit: 46feb6b495f7628a6dbf36c4e6d80faf378372d4
Patch-mainline: v4.19-rc4
References: bsc#1051510

p.port can 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/pci/switch/switchtec.c:912 ioctl_port_to_pff() warn: potential spectre issue 'pcfg->dsp_pff_inst_id' [r]

Fix this by sanitizing p.port before using it to index
pcfg->dsp_pff_inst_id

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

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Logan Gunthorpe <logang@deltatee.com>
Cc: stable@vger.kernel.org
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/pci/switch/switchtec.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -24,6 +24,8 @@
 #include <linux/cdev.h>
 #include <linux/wait.h>
 
+#include <linux/nospec.h>
+
 MODULE_DESCRIPTION("Microsemi Switchtec(tm) PCIe Management Driver");
 MODULE_VERSION("0.1");
 MODULE_LICENSE("GPL");
@@ -1155,6 +1157,8 @@ static int ioctl_port_to_pff(struct swit
 	default:
 		if (p.port > ARRAY_SIZE(pcfg->dsp_pff_inst_id))
 			return -EINVAL;
+		p.port = array_index_nospec(p.port,
+					ARRAY_SIZE(pcfg->dsp_pff_inst_id) + 1);
 		p.pff = ioread32(&pcfg->dsp_pff_inst_id[p.port - 1]);
 		break;
 	}