[PATCH 3.16 242/366] HID: hiddev: fix potential Spectre v1

[Ben Hutchings]

3.16.61-rc1 review patch.  If anyone has any objections, please let me know.

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

From: "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>

commit 4f65245f2d178b9cba48350620d76faa4a098841 upstream.

uref->field_index, uref->usage_index, finfo.field_index and cinfo.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/hid/usbhid/hiddev.c:473 hiddev_ioctl_usage() warn: potential spectre issue 'report->field' (local cap)
drivers/hid/usbhid/hiddev.c:477 hiddev_ioctl_usage() warn: potential spectre issue 'field->usage' (local cap)
drivers/hid/usbhid/hiddev.c:757 hiddev_ioctl() warn: potential spectre issue 'report->field' (local cap)
drivers/hid/usbhid/hiddev.c:801 hiddev_ioctl() warn: potential spectre issue 'hid->collection' (local cap)

Fix this by sanitizing such structure fields before using them to index
report->field, field->usage and hid->collection

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@xxxxxxxxxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/hid/usbhid/hiddev.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -35,6 +35,7 @@
 #include <linux/hiddev.h>
 #include <linux/compat.h>
 #include <linux/vmalloc.h>
+#include <linux/nospec.h>
 #include "usbhid.h"
 
 #ifdef CONFIG_USB_DYNAMIC_MINORS
@@ -478,10 +479,14 @@ static noinline int hiddev_ioctl_usage(s
 
 		if (uref->field_index >= report->maxfield)
 			goto inval;
+		uref->field_index = array_index_nospec(uref->field_index,
+						       report->maxfield);
 
 		field = report->field[uref->field_index];
 		if (uref->usage_index >= field->maxusage)
 			goto inval;
+		uref->usage_index = array_index_nospec(uref->usage_index,
+						       field->maxusage);
 
 		uref->usage_code = field->usage[uref->usage_index].hid;
 
@@ -508,6 +513,8 @@ static noinline int hiddev_ioctl_usage(s
 
 			if (uref->field_index >= report->maxfield)
 				goto inval;
+			uref->field_index = array_index_nospec(uref->field_index,
+							       report->maxfield);
 
 			field = report->field[uref->field_index];
 
@@ -761,6 +768,8 @@ static long hiddev_ioctl(struct file *fi
 
 		if (finfo.field_index >= report->maxfield)
 			break;
+		finfo.field_index = array_index_nospec(finfo.field_index,
+						       report->maxfield);
 
 		field = report->field[finfo.field_index];
 		memset(&finfo, 0, sizeof(finfo));
@@ -801,6 +810,8 @@ static long hiddev_ioctl(struct file *fi
 
 		if (cinfo.index >= hid->maxcollection)
 			break;
+		cinfo.index = array_index_nospec(cinfo.index,
+						 hid->maxcollection);
 
 		cinfo.type = hid->collection[cinfo.index].type;
 		cinfo.usage = hid->collection[cinfo.index].usage;