netdev - Re: [PATCH v2 10/35] brcmfmac: firmware: Allow platform to override macaddr

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Date:   Tue, 4 Jan 2022 16:23:41 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Hector Martin <marcan@...can.st>
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Arend van Spriel <aspriel@...il.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-hsien Lin <chi-hsien.lin@...ineon.com>,
        Wright Feng <wright.feng@...ineon.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Mark Kettenis <kettenis@...nbsd.org>,
        Rafał Miłecki <zajec5@...il.com>,
        Pieter-Paul Giesberts <pieter-paul.giesberts@...adcom.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        "John W. Linville" <linville@...driver.com>,
        "brian m. carlson" <sandals@...stytoothpaste.net>,
        "open list:TI WILINK WIRELES..." <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "open list:BROADCOM BRCM80211 IEEE802.11n WIRELESS DRIVER" 
        <brcm80211-dev-list.pdl@...adcom.com>,
        SHA-cyfmac-dev-list@...ineon.com
Subject: Re: [PATCH v2 10/35] brcmfmac: firmware: Allow platform to override macaddr

On Tue, Jan 4, 2022 at 9:29 AM Hector Martin <marcan@...can.st> wrote:
>
> On Device Tree platforms, it is customary to be able to set the MAC
> address via the Device Tree, as it is often stored in system firmware.
> This is particularly relevant for Apple ARM64 platforms, where this
> information comes from system configuration and passed through by the
> bootloader into the DT.
>
> Implement support for this by fetching the platform MAC address and
> adding or replacing the macaddr= property in nvram. This becomes the
> dongle's default MAC address.
>
> On platforms with an SROM MAC address, this overrides it. On platforms
> without one, such as Apple ARM64 devices, this is required for the
> firmware to boot (it will fail if it does not have a valid MAC at all).

...

> +#define BRCMF_FW_MACADDR_FMT                   "macaddr=%pM"
> +#define BRCMF_FW_MACADDR_LEN                   (7 + ETH_ALEN * 3)

...

>                 if (strncmp(&nvp->data[nvp->entry], "boardrev", 8) == 0)
>                         nvp->boardrev_found = true;
> +               /* strip macaddr if platform MAC overrides */
> +               if (nvp->strip_mac &&
> +                   strncmp(&nvp->data[nvp->entry], "macaddr", 7) == 0)

If it has no side effects, I would rather swap the operands of && so
you match string first (it will be in align with above code at least,
although I haven't checked bigger context).

....

> +static void brcmf_fw_add_macaddr(struct nvram_parser *nvp, u8 *mac)
> +{
> +       snprintf(&nvp->nvram[nvp->nvram_len], BRCMF_FW_MACADDR_LEN + 1,
> +                BRCMF_FW_MACADDR_FMT, mac);

Please, avoid using implict format string, it's dangerous from security p.o.v.

> +       nvp->nvram_len += BRCMF_FW_MACADDR_LEN + 1;

Also, with temporary variable the code can be better to read

size_t mac_len = ...;

> +}

-- 
With Best Regards,
Andy Shevchenko