netdev - Re: [net-next RFC PATCH v3 3/4] net: phy: aquantia: add firmware load support

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Message-ID: <6543df4e.050a0220.e42f1.2222@mx.google.com>
Date: Thu, 2 Nov 2023 18:41:31 +0100
From: Christian Marangi <ansuelsmth@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Robert Marko <robimarko@...il.com>,
	Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [net-next RFC PATCH v3 3/4] net: phy: aquantia: add firmware
 load support

On Thu, Nov 02, 2023 at 06:37:40PM +0100, Andrew Lunn wrote:
> > +/* AQR firmware doesn't have fixed offsets for iram and dram section
> > + * but instead provide an header with the offset to use on reading
> > + * and parsing the firmware.
> > + *
> > + * AQR firmware can't be trusted and each offset is validated to be
> > + * not negative and be in the size of the firmware itself.
> > + */
> > +static inline bool aqr_fw_validate_get(size_t size, size_t offset, size_t get_size)
> > +{
> > +	return size + offset > 0 && offset + get_size <= size;
> > +}
> 
> Please don't user inline in .c files. The compiler is better at
> deciding than we are.
>

OK.

> Also, i wounder about size + offset > 0. size_t is unsigned. So they
> cannot be negative. So does this test make sense?
> 

The idea was to check case where it's subtracted too much. (example
where we check the CRC at the end of the fw) but since it's unsigned i
guess it will always be zero. I will drop. (or should i use ssize_t?)

> > +static int aqr_fw_boot(struct phy_device *phydev, const u8 *data, size_t size,
> > +		       enum aqr_fw_src fw_src)
> > +{
> > +	u16 calculated_crc, read_crc, read_primary_offset;
> > +	u32 iram_offset = 0, iram_size = 0;
> > +	u32 dram_offset = 0, dram_size = 0;
> > +	char version[VERSION_STRING_SIZE];
> > +	u32 primary_offset = 0;
> > +	int ret;
> > +
> > +	/* extract saved CRC at the end of the fw
> > +	 * CRC is saved in big-endian as PHY is BE
> > +	 */
> > +	ret = aqr_fw_get_be16(data, size - sizeof(u16), size, &read_crc);
> > +	if (ret) {
> > +		phydev_err(phydev, "bad firmware CRC in firmware\n");
> > +		return ret;
> > +	}
> 
> So if size < sizeof(u16), we get a very big positive number. The > 0
> test does nothing for you here, but the other half of the test does
> trap the issue.
> 
> So i think you can remove the > 0 test.
>

Yes that single check was done because of this, but didn't notice size_t
is unsigned and it won't ever fall in negative cases.

-- 
	Ansuel