[PATCH 4.4 105/114] ptp: fix Spectre v1 vulnerability

Greg Kroah-Hartman
2018-11-08T21:52:00Z

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

commit efa61c8cf2950ab5c0e66cff3cabe2a2b24e81ba upstream.

pin_index can be 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/ptp/ptp_chardev.c:253 ptp_ioctl() warn: potential spectre issue
'ops->pin_config' [r] (local cap)

Fix this by sanitizing pin_index before using it to index
ops->pin_config, and before passing it as an argument to
function ptp_set_pinfunc(), in which it is used to index
info->pin_config.

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>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/ptp/ptp_chardev.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/drivers/ptp/ptp_chardev.c
+++ b/drivers/ptp/ptp_chardev.c
@@ -23,6 +23,8 @@
#include <linux/sched.h>
#include <linux/slab.h>

+#include <linux/nospec.h>
+
#include "ptp_private.h"

static int ptp_disable_pinfunc(struct ptp_clock_info *ops,
@@ -224,6 +226,7 @@ long ptp_ioctl(struct posix_clock *pc, u
err = -EINVAL;
break;
}
+ pin_index = array_index_nospec(pin_index, ops->n_pins);
if (mutex_lock_interruptible(&ptp->pincfg_mux))
return -ERESTARTSYS;
pd = ops->pin_config[pin_index];
@@ -242,6 +245,7 @@ long ptp_ioctl(struct posix_clock *pc, u
err = -EINVAL;
break;
}
+ pin_index = array_index_nospec(pin_index, ops->n_pins);
if (mutex_lock_interruptible(&ptp->pincfg_mux))
return -ERESTARTSYS;
err = ptp_set_pinfunc(ptp, pin_index, pd.func, pd.chan);