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    Subject[PATCH 3.16 31/99] ALSA: pcm: Fix potential Spectre v1 vulnerability
    3.16.65-rc1 review patch.  If anyone has any objections, please let me know.

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

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

    commit 94ffb030b6d31ec840bb811be455dd2e26a4f43e upstream.

    stream 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/core/pcm.c:140 snd_pcm_control_ioctl() warn: potential spectre issue 'pcm->streams' [r] (local cap)

    Fix this by sanitizing stream before using it to index pcm->streams

    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>
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    sound/core/pcm.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/sound/core/pcm.c
    +++ b/sound/core/pcm.c
    @@ -25,6 +25,7 @@
    #include <linux/time.h>
    #include <linux/mutex.h>
    #include <linux/device.h>
    +#include <linux/nospec.h>
    #include <sound/core.h>
    #include <sound/minors.h>
    #include <sound/pcm.h>
    @@ -126,6 +127,7 @@ static int snd_pcm_control_ioctl(struct
    return -EFAULT;
    if (stream < 0 || stream > 1)
    return -EINVAL;
    + stream = array_index_nospec(stream, 2);
    if (get_user(subdevice, &info->subdevice))
    return -EFAULT;
    mutex_lock(&register_mutex);
    \
     
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