misc: hmc6352: fix potential Spectre v1

val 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/misc/hmc6352.c:54 compass_store() warn: potential spectre issue
'map' [r]

Fix this by sanitizing val before using it to index map

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

Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CVE-2017-5753

(cherry picked from commit de916736aaaadddbd6061472969f667b14204aa9)
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/misc/hmc6352.c b/drivers/misc/hmc6352.c
index eeb7eef62174c4dfb5c8854efbef2d798f161f1e..38f90e17992717d7cd0f12ad904490abbaa2d1a5 100644 (file)
--- a/drivers/misc/hmc6352.c
+++ b/drivers/misc/hmc6352.c
@@ -27,6 +27,7 @@
 #include <linux/err.h>
 #include <linux/delay.h>
 #include <linux/sysfs.h>
+#include <linux/nospec.h>
 
 static DEFINE_MUTEX(compass_mutex);
 
@@ -50,6 +51,7 @@ static int compass_store(struct device *dev, const char *buf, size_t count,
                return ret;
        if (val >= strlen(map))
                return -EINVAL;
+       val = array_index_nospec(val, strlen(map));
        mutex_lock(&compass_mutex);
        ret = compass_command(c, map[val]);
        mutex_unlock(&compass_mutex);