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

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
index 9940cc70f38b..54a8b30dda38 100644
--- 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 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;
         }