linux-kernel - [PATCH 3.16 220/366] ALSA: rme9652: Hardening for potential Spectre v1

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Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Dan Carpenter" <dan.carpenter@...cle.com>,
        "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.16 220/366] ALSA: rme9652: Hardening for potential
 Spectre v1

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

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

From: Takashi Iwai <tiwai@...e.de>

commit f526afcd8f71945c23ce581d7864ace93de8a4f7 upstream.

As recently Smatch suggested, one place in RME9652 driver may expand
the array directly from the user-space value with speculation:
  sound/pci/rme9652/rme9652.c:2074 snd_rme9652_channel_info() warn: potential spectre issue 'rme9652->channel_map' (local cap)

This patch puts array_index_nospec() for hardening against it.

BugLink: https://marc.info/?l=linux-kernel&m=152411496503418&w=2
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 sound/pci/rme9652/rme9652.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/sound/pci/rme9652/rme9652.c
+++ b/sound/pci/rme9652/rme9652.c
@@ -35,6 +35,7 @@
 
 #include <asm/current.h>
 #include <asm/io.h>
+#include <linux/nospec.h>
 
 static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;	/* Index 0-MAX */
 static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;	/* ID for this card */
@@ -2059,9 +2060,10 @@ static int snd_rme9652_channel_info(stru
 	if (snd_BUG_ON(info->channel >= RME9652_NCHANNELS))
 		return -EINVAL;
 
-	if ((chn = rme9652->channel_map[info->channel]) < 0) {
+	chn = rme9652->channel_map[array_index_nospec(info->channel,
+						      RME9652_NCHANNELS)];
+	if (chn < 0)
 		return -EINVAL;
-	}
 
 	info->offset = chn * RME9652_CHANNEL_BUFFER_BYTES;
 	info->first = 0;