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

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

index 1bff4b1b39cd..ba99ff0e93e0 100644
@@ -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;

2.19.2

Hi,

[This is an automated email]

This commit has been processed because it contains a -stable tag. The stable tag indicates that it's relevant for the following trees: all

The bot has tested the following trees: v4.19.10, v4.14.89, v4.9.146, v4.4.168, v3.18.130,

v4.19.10: Build OK!
v4.14.89: Build OK!
v4.9.146: Build OK!
v4.4.168: Build OK!
v3.18.130: Failed to apply! Possible dependencies:
6cbbfe1c8ddb ("ALSA: Include linux/io.h instead of asm/io.h")

How should we proceed with this patch?

--
Thanks,
Sasha

Applied, thanks.

Takashi