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Message-ID: <54d4ffb1-1488-1a4f-58b2-8b3471389729@linux.intel.com>
Date: Fri, 10 Feb 2023 14:10:56 +0100
From: Amadeusz Sławiński
<amadeuszx.slawinski@...ux.intel.com>
To: Kees Cook <keescook@...omium.org>,
Cezary Rojewski <cezary.rojewski@...el.com>
Cc: Sasa Ostrouska <casaxa@...il.com>,
Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
Bard Liao <yung-chuan.liao@...ux.intel.com>,
Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
Mark Brown <broonie@...nel.org>, Takashi Iwai <tiwai@...e.com>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ASoC: Intel: Skylake: Replace 1-element array with
flex-array
On 2/10/2023 6:14 AM, Kees Cook wrote:
> The kernel is globally removing the ambiguous 0-length and 1-element
> arrays in favor of flexible arrays, so that we can gain both compile-time
> and run-time array bounds checking[1]. In this instance, struct
> skl_cpr_cfg contains struct skl_cpr_gtw_cfg, which defined "config_data"
> as a 1-element array.
>
> Normally when switching from a 1-element array to a flex-array, any
> related size calculations must be adjusted too. However, it seems the
> original code was over-allocating space, since 1 extra u32 would be
> included by the sizeof():
>
> param_size = sizeof(struct skl_cpr_cfg);
> param_size += mconfig->formats_config[SKL_PARAM_INIT].caps_size;
>
> But the copy uses caps_size bytes, and cap_size / 4 (i.e. sizeof(u32))
> for the length tracking:
>
> memcpy(cpr_mconfig->gtw_cfg.config_data,
> mconfig->formats_config[SKL_PARAM_INIT].caps,
> mconfig->formats_config[SKL_PARAM_INIT].caps_size);
>
> cpr_mconfig->gtw_cfg.config_length =
> (mconfig->formats_config[SKL_PARAM_INIT].caps_size) / 4;
>
> Therefore, no size calculations need adjusting. Change the struct
> skl_cpr_gtw_cfg config_data member to be a true flexible array, which
> also fixes the over-allocation, and silences this memcpy run-time false
> positive:
>
> memcpy: detected field-spanning write (size 100) of single field "cpr_mconfig->gtw_cfg.config_data" at sound/soc/intel/skylake/skl-messages.c:554 (size 4)
>
> [1] For lots of details, see both:
> https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
> https://people.kernel.org/kees/bounded-flexible-arrays-in-c
>
> Reported-by: Sasa Ostrouska <casaxa@...il.com>
> Link: https://lore.kernel.org/all/CALFERdwvq5day_sbDfiUsMSZCQu9HG8-SBpOZDNPeMdZGog6XA@mail.gmail.com/
> Cc: Cezary Rojewski <cezary.rojewski@...el.com>
> Cc: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> Cc: Liam Girdwood <liam.r.girdwood@...ux.intel.com>
> Cc: Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>
> Cc: Bard Liao <yung-chuan.liao@...ux.intel.com>
> Cc: Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>
> Cc: Kai Vehmanen <kai.vehmanen@...ux.intel.com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Jaroslav Kysela <perex@...ex.cz>
> Cc: Takashi Iwai <tiwai@...e.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: "Amadeusz Sławiński" <amadeuszx.slawinski@...ux.intel.com>
> Cc: alsa-devel@...a-project.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> sound/soc/intel/skylake/skl-topology.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/soc/intel/skylake/skl-topology.h b/sound/soc/intel/skylake/skl-topology.h
> index 6db0fd7bad49..ad94f8020c27 100644
> --- a/sound/soc/intel/skylake/skl-topology.h
> +++ b/sound/soc/intel/skylake/skl-topology.h
> @@ -115,7 +115,7 @@ struct skl_cpr_gtw_cfg {
> u32 dma_buffer_size;
> u32 config_length;
> /* not mandatory; required only for DMIC/I2S */
> - u32 config_data[1];
> + u32 config_data[];
> } __packed;
>
> struct skl_dma_control {
This fails in our validation. Maybe we can use the union workaround, to
leave the size as is?
Following seems to work in manual test:
diff --git a/sound/soc/intel/skylake/skl-topology.h
b/sound/soc/intel/skylake/skl-topology.h
index 6db0fd7bad49..ffbd2e60fede 100644
--- a/sound/soc/intel/skylake/skl-topology.h
+++ b/sound/soc/intel/skylake/skl-topology.h
@@ -115,7 +115,10 @@ struct skl_cpr_gtw_cfg {
u32 dma_buffer_size;
u32 config_length;
/* not mandatory; required only for DMIC/I2S */
- u32 config_data[1];
+ union {
+ u32 x;
+ u32 config_data[0];
+ };
} __packed;
struct skl_dma_control {
I can also run it through validation to make sure if it is acceptable.
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