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Subject[PATCH 4.4 30/88] ALSA: rme9652: Fix potential Spectre v1 vulnerability
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Gustavo A. R. Silva <gustavo@embeddedor.com>

commit 0b84304ef5da92add8dc75a1b07879c5374cdb05 upstream.

info->channel is indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

sound/pci/rme9652/hdsp.c:4100 snd_hdsp_channel_info() warn: potential spectre issue 'hdsp->channel_map' [r] (local cap)

Fix this by sanitizing info->channel before using it to index hdsp->channel_map

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

Also, notice that I refactored the code a bit in order to get rid of the
following checkpatch warning:

ERROR: do not use assignment in if condition
FILE: sound/pci/rme9652/hdsp.c:4103:
if ((mapped_channel = hdsp->channel_map[info->channel]) < 0)

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/pci/rme9652/hdsp.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/sound/pci/rme9652/hdsp.c
+++ b/sound/pci/rme9652/hdsp.c
@@ -30,6 +30,7 @@
#include <linux/math64.h>
#include <linux/vmalloc.h>
#include <linux/io.h>
+#include <linux/nospec.h>

#include <sound/core.h>
#include <sound/control.h>
@@ -4065,15 +4066,16 @@ static int snd_hdsp_channel_info(struct
struct snd_pcm_channel_info *info)
{
struct hdsp *hdsp = snd_pcm_substream_chip(substream);
- int mapped_channel;
+ unsigned int channel = info->channel;

- if (snd_BUG_ON(info->channel >= hdsp->max_channels))
+ if (snd_BUG_ON(channel >= hdsp->max_channels))
return -EINVAL;
+ channel = array_index_nospec(channel, hdsp->max_channels);

- if ((mapped_channel = hdsp->channel_map[info->channel]) < 0)
+ if (hdsp->channel_map[channel] < 0)
return -EINVAL;

- info->offset = mapped_channel * HDSP_CHANNEL_BUFFER_BYTES;
+ info->offset = hdsp->channel_map[channel] * HDSP_CHANNEL_BUFFER_BYTES;
info->first = 0;
info->step = 32;
return 0;

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