linux-kernel - [PATCH 3.16 057/202] char/mwave: fix potential Spectre v1 vulnerability

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Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: [PATCH 3.16 057/202] char/mwave: fix potential Spectre v1
 vulnerability

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

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

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

commit 701956d4018e5d5438570e39e8bda47edd32c489 upstream.

ipcnum 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/char/mwave/mwavedd.c:299 mwave_ioctl() warn: potential spectre issue 'pDrvData->IPCs' [w] (local cap)

Fix this by sanitizing ipcnum before using it to index pDrvData->IPCs.

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@...eddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/char/mwave/mwavedd.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/char/mwave/mwavedd.c
+++ b/drivers/char/mwave/mwavedd.c
@@ -59,6 +59,7 @@
 #include <linux/mutex.h>
 #include <linux/delay.h>
 #include <linux/serial_8250.h>
+#include <linux/nospec.h>
 #include "smapi.h"
 #include "mwavedd.h"
 #include "3780i.h"
@@ -289,6 +290,8 @@ static long mwave_ioctl(struct file *fil
 						ipcnum);
 				return -EINVAL;
 			}
+			ipcnum = array_index_nospec(ipcnum,
+						    ARRAY_SIZE(pDrvData->IPCs));
 			PRINTK_3(TRACE_MWAVE,
 				"mwavedd::mwave_ioctl IOCTL_MW_REGISTER_IPC"
 				" ipcnum %x entry usIntCount %x\n",
@@ -317,6 +320,8 @@ static long mwave_ioctl(struct file *fil
 						" Invalid ipcnum %x\n", ipcnum);
 				return -EINVAL;
 			}
+			ipcnum = array_index_nospec(ipcnum,
+						    ARRAY_SIZE(pDrvData->IPCs));
 			PRINTK_3(TRACE_MWAVE,
 				"mwavedd::mwave_ioctl IOCTL_MW_GET_IPC"
 				" ipcnum %x, usIntCount %x\n",
@@ -383,6 +388,8 @@ static long mwave_ioctl(struct file *fil
 						ipcnum);
 				return -EINVAL;
 			}
+			ipcnum = array_index_nospec(ipcnum,
+						    ARRAY_SIZE(pDrvData->IPCs));
 			mutex_lock(&mwave_mutex);
 			if (pDrvData->IPCs[ipcnum].bIsEnabled == TRUE) {
 				pDrvData->IPCs[ipcnum].bIsEnabled = FALSE;