On Fri, Feb 10, 2023 at 02:10:56PM +0100, Amadeusz Sławiński wrote: > 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@xxxxxxxxx> > > Link: https://lore.kernel.org/all/CALFERdwvq5day_sbDfiUsMSZCQu9HG8-SBpOZDNPeMdZGog6XA@xxxxxxxxxxxxxx/ > > Cc: Cezary Rojewski <cezary.rojewski@xxxxxxxxx> > > Cc: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> > > Cc: Liam Girdwood <liam.r.girdwood@xxxxxxxxxxxxxxx> > > Cc: Peter Ujfalusi <peter.ujfalusi@xxxxxxxxxxxxxxx> > > Cc: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx> > > Cc: Ranjani Sridharan <ranjani.sridharan@xxxxxxxxxxxxxxx> > > Cc: Kai Vehmanen <kai.vehmanen@xxxxxxxxxxxxxxx> > > Cc: Mark Brown <broonie@xxxxxxxxxx> > > Cc: Jaroslav Kysela <perex@xxxxxxxx> > > Cc: Takashi Iwai <tiwai@xxxxxxxx> > > Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx> > > Cc: "Amadeusz Sławiński" <amadeuszx.slawinski@xxxxxxxxxxxxxxx> > > Cc: alsa-devel@xxxxxxxxxxxxxxxx > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > 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. Ah, okay. Thanks for checking! > 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]; > + }; Yeah, that could work, though the last member would be: DECLARE_FLEX_ARRAY(u32, config_data); otherwise the array is 0 length (rather than a proper flex array). But before that, let me see if I can track down where the size is being used, in case we can avoid adding the padding. -- Kees Cook
