linux-kernel - [PATCH 4.18 041/158] switchtec: Fix Spectre v1 vulnerability

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Message-Id: <20180917211713.077768468@linuxfoundation.org>
Date:   Tue, 18 Sep 2018 00:41:11 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: [PATCH 4.18 041/158] switchtec: Fix Spectre v1 vulnerability

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gustavo A. R. Silva <gustavo@...eddedor.com>

commit 46feb6b495f7628a6dbf36c4e6d80faf378372d4 upstream.

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@...eddedor.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Acked-by: Logan Gunthorpe <logang@...tatee.com>
Cc: stable@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -14,6 +14,8 @@
 #include <linux/poll.h>
 #include <linux/wait.h>

+#include <linux/nospec.h>
+
 MODULE_DESCRIPTION("Microsemi Switchtec(tm) PCIe Management Driver");
 MODULE_VERSION("0.1");
 MODULE_LICENSE("GPL");
@@ -909,6 +911,8 @@ 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;
 	}