[PATCH 4.4 23/44] ALSA: rme9652: Hardening for potential Spectre v1

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Takashi Iwai <tiwai@xxxxxxx>

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@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 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
@@ -26,6 +26,7 @@
 #include <linux/pci.h>
 #include <linux/module.h>
 #include <linux/io.h>
+#include <linux/nospec.h>
 
 #include <sound/core.h>
 #include <sound/control.h>
@@ -2036,9 +2037,10 @@ 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;