linux-hardening - Re: [PATCH v3 net-next 5/8] mfd: zl3073x: Add functions to work with register mailboxes

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Message-ID: <d286dec9-a544-409d-bf62-d2b84ef6ecd4@lunn.ch>
Date: Wed, 16 Apr 2025 19:32:12 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Ivan Vecera <ivecera@...hat.com>
Cc: netdev@...r.kernel.org, Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
	Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
	Jiri Pirko <jiri@...nulli.us>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Prathosh Satish <Prathosh.Satish@...rochip.com>,
	Lee Jones <lee@...nel.org>, Kees Cook <kees@...nel.org>,
	Andy Shevchenko <andy@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Schmidt <mschmidt@...hat.com>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 net-next 5/8] mfd: zl3073x: Add functions to work with
 register mailboxes

> +/**
> + * zl3073x_mb_dpll_read - read given DPLL configuration to mailbox
> + * @zldev: pointer to device structure
> + * @index: DPLL index
> + *
> + * Reads configuration of given DPLL into DPLL mailbox.
> + *
> + * Context: Process context. Expects zldev->regmap_lock to be held by caller.
> + * Return: 0 on success, <0 on error
> + */
> +int zl3073x_mb_dpll_read(struct zl3073x_dev *zldev, u8 index)
> +{
> +	int rc;

lockdep_assert_held(zldev->regmap_lock) is stronger than having a
comment. When talking about i2c and spi devices, it costs nothing, and
catches bugs early.

> +/*
> + * Mailbox operations
> + */
> +int zl3073x_mb_dpll_read(struct zl3073x_dev *zldev, u8 index);
> +int zl3073x_mb_dpll_write(struct zl3073x_dev *zldev, u8 index);
> +int zl3073x_mb_output_read(struct zl3073x_dev *zldev, u8 index);
> +int zl3073x_mb_output_write(struct zl3073x_dev *zldev, u8 index);
> +int zl3073x_mb_ref_read(struct zl3073x_dev *zldev, u8 index);
> +int zl3073x_mb_ref_write(struct zl3073x_dev *zldev, u8 index);
> +int zl3073x_mb_synth_read(struct zl3073x_dev *zldev, u8 index);
> +int zl3073x_mb_synth_write(struct zl3073x_dev *zldev, u8 index);

I assume these are the only valid ways to access a mailbox?

If so:

> +static inline __maybe_unused int
> +zl3073x_mb_read_ref_mb_mask(struct zl3073x_dev *zldev, u16 *value)
> +{
> +	__be16 temp;
> +	int rc;
> +
> +	lockdep_assert_held(&zldev->mailbox_lock);
> +	rc = regmap_bulk_read(zldev->regmap, ZL_REG_REF_MB_MASK, &temp,
> +			      sizeof(temp));
> +	if (rc)
> +		return rc;
> +
> +	*value = be16_to_cpu(temp);
> +	return rc;
> +}

These helpers can be made local to the core. You can then drop the
lockdep_assert_held() from here, since the only way to access them is
via the API you defined above, and add the checks in those API
functions.

	Andrew