[PATCH 4.16 041/113] ALSA: opl3: Hardening for potential Spectre v1

[Greg Kroah-Hartman]

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

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

From: Takashi Iwai <tiwai@xxxxxxx>

commit 7f054a5bee0987f1e2d4e59daea462421c76f2cb upstream.

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

---
 sound/drivers/opl3/opl3_synth.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- 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
 {
 	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
 		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 */