ALSA: opl3: Hardening for potential Spectre v1

As recently Smatch suggested, one place in OPL3 driver may expand the
array directly from the user-space value with speculation:
  sound/drivers/opl3/opl3_synth.c:476 snd_opl3_set_voice() warn: potential spectre issue 'snd_opl3_regmap'

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@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 5 insertions, 2 deletions

diff --git a/sound/drivers/opl3/opl3_synth.c b/sound/drivers/opl3/opl3_synth.c
index ddcc1a325a61..42920a243328 100644
--- a/sound/drivers/opl3/opl3_synth.c
+++ b/sound/drivers/opl3/opl3_synth.c
@@ -21,6 +21,7 @@
 
 #include <linux/slab.h>
 #include <linux/export.h>
+#include <linux/nospec.h>
 #include <sound/opl3.h>
 #include <sound/asound_fm.h>
 
@@ -448,7 +449,7 @@ static int snd_opl3_set_voice(struct snd_opl3 * opl3, struct snd_dm_fm_voice * v
 {
         unsigned short reg_side;
         unsigned char op_offset;
-        unsigned char voice_offset;
+        unsigned char voice_offset, voice_op;
 
         unsigned short opl3_reg;
         unsigned char reg_val;
@@ -473,7 +474,9 @@ static int snd_opl3_set_voice(struct snd_opl3 * opl3, struct snd_dm_fm_voice * v
                 voice_offset = voice->voice - MAX_OPL2_VOICES;
         }
         /* Get register offset of operator */
-        op_offset = snd_opl3_regmap[voice_offset][voice->op];
+        voice_offset = array_index_nospec(voice_offset, MAX_OPL2_VOICES);
+        voice_op = array_index_nospec(voice->op, 4);
+        op_offset = snd_opl3_regmap[voice_offset][voice_op];
 
         reg_val = 0x00;
         /* Set amplitude modulation (tremolo) effect */