[PATCH] ALSA: isa/wavefront: Fix potential Spectre v1 vulnerabilities

From: Gustavo A. R. Silva
Date: Tue Mar 26 2019 - 14:32:10 EST


header->number and i are 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/isa/wavefront/wavefront_synth.c:792 wavefront_send_patch() warn: potential spectre issue 'dev->patch_status' [w] (local cap)
sound/isa/wavefront/wavefront_synth.c:819 wavefront_send_program() warn: potential spectre issue 'dev->prog_status' [w] (local cap)
sound/isa/wavefront/wavefront_synth.c:1197 wavefront_send_alias() warn: potential spectre issue 'dev->sample_status' [w]
sound/isa/wavefront/wavefront_synth.c:1248 wavefront_send_multisample() warn: potential spectre issue 'dev->sample_status' [w]
sound/isa/wavefront/wavefront_synth.c:1548 wavefront_synth_control() warn: potential spectre issue 'dev->sample_status' [r] (local cap)

Fix this by sanitizing header->number and i before using them to index
dev->patch_status, dev->prog_status, dev->sample_status.

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].

[1] https://lore.kernel.org/lkml/20180423164740.GY17484@xxxxxxxxxxxxxx/

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
sound/isa/wavefront/wavefront_synth.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/sound/isa/wavefront/wavefront_synth.c b/sound/isa/wavefront/wavefront_synth.c
index 0b1e4b34b299..a78e125dfdf9 100644
--- a/sound/isa/wavefront/wavefront_synth.c
+++ b/sound/isa/wavefront/wavefront_synth.c
@@ -31,6 +31,7 @@
#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/module.h>
+#include <linux/nospec.h>
#include <sound/core.h>
#include <sound/snd_wavefront.h>
#include <sound/initval.h>
@@ -788,6 +789,8 @@ wavefront_send_patch (snd_wavefront_t *dev, wavefront_patch_info *header)

if (header->number >= ARRAY_SIZE(dev->patch_status))
return -EINVAL;
+ header->number = array_index_nospec(header->number,
+ ARRAY_SIZE(dev->patch_status));

dev->patch_status[header->number] |= WF_SLOT_FILLED;

@@ -815,6 +818,8 @@ wavefront_send_program (snd_wavefront_t *dev, wavefront_patch_info *header)

if (header->number >= ARRAY_SIZE(dev->prog_status))
return -EINVAL;
+ header->number = array_index_nospec(header->number,
+ ARRAY_SIZE(dev->prog_status));

dev->prog_status[header->number] = WF_SLOT_USED;

@@ -1194,6 +1199,11 @@ wavefront_send_alias (snd_wavefront_t *dev, wavefront_patch_info *header)
return -EIO;
}

+ if (header->number >= ARRAY_SIZE(dev->sample_status))
+ return -EINVAL;
+ header->number = array_index_nospec(header->number,
+ ARRAY_SIZE(dev->sample_status));
+
dev->sample_status[header->number] = (WF_SLOT_FILLED|WF_ST_ALIAS);

return (0);
@@ -1245,6 +1255,12 @@ wavefront_send_multisample (snd_wavefront_t *dev, wavefront_patch_info *header)
return -EIO;
}

+ if (header->number >= ARRAY_SIZE(dev->sample_status)) {
+ kfree(msample_hdr);
+ return -EINVAL;
+ }
+ header->number = array_index_nospec(header->number,
+ ARRAY_SIZE(dev->sample_status));
dev->sample_status[header->number] = (WF_SLOT_FILLED|WF_ST_MULTISAMPLE);

kfree(msample_hdr);
@@ -1545,6 +1561,7 @@ wavefront_synth_control (snd_wavefront_card_t *acard,
wc->status = EINVAL;
return -EINVAL;
}
+ i = array_index_nospec(i, WF_MAX_SAMPLE);
wc->rbuf[0] = dev->sample_status[i];
wc->status = 0;
return 0;
--
2.21.0