linux-hardening - Re: [PATCH net-next v4 5/8] mfd: zl3073x: Add functions to work with register mailboxes

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Message-ID: <5094e051-5504-48a5-b411-ed1a0d949eeb@lunn.ch>
Date: Thu, 24 Apr 2025 18:43:32 +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 net-next v4 5/8] mfd: zl3073x: Add functions to work with
 register mailboxes

> +static int
> +zl3073x_write_reg(struct zl3073x_dev *zldev, unsigned int reg, const void *val)
> +{
> +	unsigned int len;
> +	u8 buf[6];
> +	int rc;
> +
> +	/* Offset of the last item in the indexed register or offset of
> +	 * the non-indexed register itself.
> +	 */
> +	if (ZL_REG_OFFSET(reg) > ZL_REG_MAX_OFFSET(reg)) {
> +		dev_err(zldev->dev, "Index of out range for reg 0x%04lx\n",
> +			ZL_REG_ADDR(reg));
> +		return -EINVAL;
> +	}
> +
> +	len = ZL_REG_SIZE(reg);

I suggested you add helpers for zl3073x_write_reg_u8(),
zl3073x_write_reg_u16(), zl3073x_write_reg_32(), and
zl3073x_write_reg_48(). The compiler will then do type checking for
val, ensure what you pass is actually big enough.

Here you have a void *val. You have no idea how big a value that
pointer points to, and the compiler is not helping you.

I suggest you add the individual helpers. If you decided to keep the
register meta data, you can validate the correct helper has been
called.

	Andrew