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    Subject[PATCH 4.9 33/71] ALSA: emux: Fix potential Spectre v1 vulnerabilities
    Date
    4.9-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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