linux-kernel - Re: [PATCH] ASoC: cros_ec_codec: fix uninitialized memory read

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Date:   Fri, 4 Dec 2020 10:56:06 +0800
From:   Tzung-Bi Shih <tzungbi@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Cheng-Yi Chiang <cychiang@...omium.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Arnd Bergmann <arnd@...db.de>,
        Guenter Roeck <groeck@...omium.org>,
        ALSA development <alsa-devel@...a-project.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: cros_ec_codec: fix uninitialized memory read

On Fri, Dec 4, 2020 at 6:55 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> gcc points out a memory area that is copied to a device
> but not initialized:
>
> sound/soc/codecs/cros_ec_codec.c: In function 'i2s_rx_event':
> arch/x86/include/asm/string_32.h:83:20: error: '*((void *)&p+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    83 |   *((int *)to + 1) = *((int *)from + 1);
>
> Initialize all the unused fields to zero.
>
> Fixes: 727f1c71c780 ("ASoC: cros_ec_codec: refactor I2S RX")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Tzung-Bi Shih <tzungbi@...gle.com>

In the case in i2s_rx_event(), only the "cmd" member is used.  But it
is fine to please the compiler.

struct __ec_align4 ec_param_ec_codec_i2s_rx {
        uint8_t cmd; /* enum ec_codec_i2s_rx_subcmd */
        uint8_t reserved[3];

        union {
            ...
        };
};

I am a bit curious about, in other use cases of
ec_param_ec_codec_i2s_rx, why the compiler doesn't complain about
uninitialization of the "reserved" member?