linux-kernel - Re: [PATCH 00/14] ASoC: Constify local snd_sof_dsp

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Message-ID: <3acfbe3c-8b83-4c40-83c2-437f963fd25a@linux.intel.com>
Date: Mon, 22 Apr 2024 15:42:00 -0500
From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, Liam Girdwood
 <lgirdwood@...il.com>, Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
 Bard Liao <yung-chuan.liao@...ux.intel.com>,
 Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
 Daniel Baluta <daniel.baluta@....com>,
 Kai Vehmanen <kai.vehmanen@...ux.intel.com>, Mark Brown
 <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Matthias Brugger
 <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: sound-open-firmware@...a-project.org, linux-sound@...r.kernel.org,
 linux-kernel@...r.kernel.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 00/14] ASoC: Constify local snd_sof_dsp_ops


> There are multiple reasons and benefits for const, like compiler
> optimization, code readability (meaning) up to security improvements,
> e.g. by some GCC plugins or marking rodata as really non-writeable, so
> closing some ways of exploits. There are many opportunities here, even
> if they are not yet enabled.

Possibly, but the SOF core does not know if the structure it uses is
rodata or not. Using the 'const' identifier would be misleading.

>> that's a different interpretation to the 'software' view you're
>> describing. "this structure will not modified by this function" is not
>> the same thing as "this structure CANNOT be modified".
> 
> Yes, but can we please discuss specific patchset then? Patches which
> change pointers to const have one "interpretation". Patches which modify
> static or global data have another.

Just look at sound/soc/sof/intel/mtl.c... The core will sometimes use a
constant structure and sometimes not, depending on the PCI ID reported
by hardware. This was intentional to override common defaults and make
the differences limited in scope between hardware generations.

int sof_mtl_ops_init(struct snd_sof_dev *sdev)
{
	struct sof_ipc4_fw_data *ipc4_data;

	/* common defaults */
	memcpy(&sof_mtl_ops, &sof_hda_common_ops, sizeof(struct
snd_sof_dsp_ops)); <<<< THE BASELINE IS CONSTANT

        <<< THE REST ISN'T.

	/* shutdown */
	sof_mtl_ops.shutdown = hda_dsp_shutdown;

	/* doorbell */
	sof_mtl_ops.irq_thread = mtl_ipc_irq_thread;

	/* ipc */
	sof_mtl_ops.send_msg = mtl_ipc_send_msg;
	sof_mtl_ops.get_mailbox_offset = mtl_dsp_ipc_get_mailbox_offset;
	sof_mtl_ops.get_window_offset = mtl_dsp_ipc_get_window_offset;

	/* debug */
	sof_mtl_ops.debug_map = mtl_dsp_debugfs;
	sof_mtl_ops.debug_map_count = ARRAY_SIZE(mtl_dsp_debugfs);
	sof_mtl_ops.dbg_dump = mtl_dsp_dump;
	sof_mtl_ops.ipc_dump = mtl_ipc_dump;