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Subject[PATCH 4.4 33/88] ALSA: emux: Fix potential Spectre v1 vulnerabilities
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

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

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

commit 4aea96f4237cea0c51a8bc87c0db31f0f932f1f0 upstream.

info.mode and info.port are indirectly controlled by user-space,
hence leading to a potential exploitation of the Spectre variant 1
vulnerability.

These issues were detected with the help of Smatch:

sound/synth/emux/emux_hwdep.c:72 snd_emux_hwdep_misc_mode() warn: potential spectre issue 'emu->portptrs[i]->ctrls' [w] (local cap)
sound/synth/emux/emux_hwdep.c:75 snd_emux_hwdep_misc_mode() warn: potential spectre issue 'emu->portptrs' [w] (local cap)
sound/synth/emux/emux_hwdep.c:75 snd_emux_hwdep_misc_mode() warn: potential spectre issue 'emu->portptrs[info.port]->ctrls' [w] (local cap)

Fix this by sanitizing both info.mode and info.port before using them
to index emu->portptrs[i]->ctrls, emu->portptrs[info.port]->ctrls and
emu->portptrs.

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

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

---
sound/synth/emux/emux_hwdep.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/sound/synth/emux/emux_hwdep.c
+++ b/sound/synth/emux/emux_hwdep.c
@@ -22,9 +22,9 @@
#include <sound/core.h>
#include <sound/hwdep.h>
#include <linux/uaccess.h>
+#include <linux/nospec.h>
#include "emux_voice.h"

-
#define TMP_CLIENT_ID 0x1001

/*
@@ -66,13 +66,16 @@ snd_emux_hwdep_misc_mode(struct snd_emux
return -EFAULT;
if (info.mode < 0 || info.mode >= EMUX_MD_END)
return -EINVAL;
+ info.mode = array_index_nospec(info.mode, EMUX_MD_END);

if (info.port < 0) {
for (i = 0; i < emu->num_ports; i++)
emu->portptrs[i]->ctrls[info.mode] = info.value;
} else {
- if (info.port < emu->num_ports)
+ if (info.port < emu->num_ports) {
+ info.port = array_index_nospec(info.port, emu->num_ports);
emu->portptrs[info.port]->ctrls[info.mode] = info.value;
+ }
}
return 0;
}

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