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    Subject[PATCH 4.9 30/71] ALSA: rme9652: Fix potential Spectre v1 vulnerability
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

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

    commit 0b84304ef5da92add8dc75a1b07879c5374cdb05 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

    --- a/sound/pci/rme9652/hdsp.c
    +++ b/sound/pci/rme9652/hdsp.c
    @@ -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>
    @@ -4065,15 +4066,16 @@ static int snd_hdsp_channel_info(struct
    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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