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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id l22-20020a62be16000000b005943bd7c72bsm3595216pff.190.2023.02.10.11.06.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Feb 2023 11:06:40 -0800 (PST) Message-ID: <63e695c0.620a0220.f69b1.6eec@mx.google.com> X-Google-Original-Message-ID: <202302101104.@keescook> Date: Fri, 10 Feb 2023 11:06:40 -0800 From: Kees Cook To: Amadeusz =?utf-8?B?U8WCYXdpxYRza2k=?= Cc: Cezary Rojewski , Sasa Ostrouska , Pierre-Louis Bossart , Liam Girdwood , Peter Ujfalusi , Bard Liao , Ranjani Sridharan , Kai Vehmanen , Mark Brown , Takashi Iwai , "Gustavo A. R. Silva" , alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] ASoC: Intel: Skylake: Replace 1-element array with flex-array References: <20230210051447.never.204-kees@kernel.org> <54d4ffb1-1488-1a4f-58b2-8b3471389729@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <54d4ffb1-1488-1a4f-58b2-8b3471389729@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > Link: https://lore.kernel.org/all/CALFERdwvq5day_sbDfiUsMSZCQu9HG8-SBpOZDNPeMdZGog6XA@mail.gmail.com/ > > Cc: Cezary Rojewski > > Cc: Pierre-Louis Bossart > > Cc: Liam Girdwood > > Cc: Peter Ujfalusi > > Cc: Bard Liao > > Cc: Ranjani Sridharan > > Cc: Kai Vehmanen > > Cc: Mark Brown > > Cc: Jaroslav Kysela > > Cc: Takashi Iwai > > Cc: "Gustavo A. R. Silva" > > Cc: "Amadeusz Sławiński" > > Cc: alsa-devel@alsa-project.org > > Signed-off-by: Kees Cook > > --- > > 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