Commit 0b84304e authored Dec 18, 2018 by Gustavo A. R. Silva Committed by Takashi Iwai Dec 19, 2018

ALSA: rme9652: Fix potential Spectre v1 vulnerability

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>

parent ed49e839

sound/pci/rme9652/hdsp.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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>
		@@ -4092,15 +4093,16 @@ static int snd_hdsp_channel_info(struct snd_pcm_substream *substream,
		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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