switchtec: Fix Spectre v1 vulnerability

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
CVE-2017-5753

(cherry picked from commit 46feb6b495f7628a6dbf36c4e6d80faf378372d4)
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
index 730cc897b94da0251dac161192fd1bf1fc47b324..cc4103b4671b4e5e0d94f0b6df03025003f7af1b 100644 (file)
--- a/drivers/pci/switch/switchtec.c
+++ b/drivers/pci/switch/switchtec.c
@@ -23,6 +23,8 @@
 #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");
@@ -917,6 +919,8 @@ static int ioctl_port_to_pff(struct switchtec_dev *stdev,
        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;
        }