ALSA: hdspm: Hardening for potential Spectre v1

As recently Smatch suggested, a couple of places in HDSP MADI driver
may expand the array directly from the user-space value with
speculation:
  sound/pci/rme9652/hdspm.c:5717 snd_hdspm_channel_info() warn: potential spectre issue 'hdspm->channel_map_out' (local cap)
  sound/pci/rme9652/hdspm.c:5734 snd_hdspm_channel_info() warn: potential spectre issue 'hdspm->channel_map_in' (local cap)

This patch puts array_index_nospec() for hardening against them.

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>

diff --git a/sound/pci/rme9652/hdspm.c b/sound/pci/rme9652/hdspm.c
index 4c59983158e0ed8d37bcad8ae3735129a1bd1ef8..11b5b5e0e0580fd3a3d33cf99dd71728db1bdd3a 100644 (file)
--- a/sound/pci/rme9652/hdspm.c
+++ b/sound/pci/rme9652/hdspm.c
@@ -137,6 +137,7 @@
 #include <linux/pci.h>
 #include <linux/math64.h>
 #include <linux/io.h>
+#include <linux/nospec.h>
 
 #include <sound/core.h>
 #include <sound/control.h>
@@ -5698,40 +5699,43 @@ static int snd_hdspm_channel_info(struct snd_pcm_substream *substream,
                struct snd_pcm_channel_info *info)
 {
        struct hdspm *hdspm = snd_pcm_substream_chip(substream);
+       unsigned int channel = info->channel;
 
        if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
-               if (snd_BUG_ON(info->channel >= hdspm->max_channels_out)) {
+               if (snd_BUG_ON(channel >= hdspm->max_channels_out)) {
                        dev_info(hdspm->card->dev,
                                 "snd_hdspm_channel_info: output channel out of range (%d)\n",
-                                info->channel);
+                                channel);
                        return -EINVAL;
                }
 
-               if (hdspm->channel_map_out[info->channel] < 0) {
+               channel = array_index_nospec(channel, hdspm->max_channels_out);
+               if (hdspm->channel_map_out[channel] < 0) {
                        dev_info(hdspm->card->dev,
                                 "snd_hdspm_channel_info: output channel %d mapped out\n",
-                                info->channel);
+                                channel);
                        return -EINVAL;
                }
 
-               info->offset = hdspm->channel_map_out[info->channel] *
+               info->offset = hdspm->channel_map_out[channel] *
                        HDSPM_CHANNEL_BUFFER_BYTES;
        } else {
-               if (snd_BUG_ON(info->channel >= hdspm->max_channels_in)) {
+               if (snd_BUG_ON(channel >= hdspm->max_channels_in)) {
                        dev_info(hdspm->card->dev,
                                 "snd_hdspm_channel_info: input channel out of range (%d)\n",
-                                info->channel);
+                                channel);
                        return -EINVAL;
                }
 
-               if (hdspm->channel_map_in[info->channel] < 0) {
+               channel = array_index_nospec(channel, hdspm->max_channels_in);
+               if (hdspm->channel_map_in[channel] < 0) {
                        dev_info(hdspm->card->dev,
                                 "snd_hdspm_channel_info: input channel %d mapped out\n",
-                                info->channel);
+                                channel);
                        return -EINVAL;
                }
 
-               info->offset = hdspm->channel_map_in[info->channel] *
+               info->offset = hdspm->channel_map_in[channel] *
                        HDSPM_CHANNEL_BUFFER_BYTES;
        }