linux-hardening - Re: [PATCH 1/2] USB: EHCI: Add register array bounds to HCS ports

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Message-ID: <CAHp75VdE3akTqmJ6VE4+Q4F959JscvZpiJok4=2JmjDjubtuxw@mail.gmail.com>
Date:   Wed, 18 Aug 2021 12:48:17 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Al Cooper <alcooperx@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-usb@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 1/2] USB: EHCI: Add register array bounds to HCS ports

On Wed, Aug 18, 2021 at 7:30 AM Kees Cook <keescook@...omium.org> wrote:
>
> The original EHCI register struct used a trailing 0-element array for
> addressing the N_PORTS-many available registers. However, after
> commit a46af4ebf9ff ("USB: EHCI: define extension registers like normal ones")
> the 0-element array started to overlap the USBMODE extension register.
>
> To avoid future compile-time warnings about accessing indexes within a
> 0-element array, rearrange the struct to actually describe the expected
> layout (max 15 registers) with a union. All offsets remain the same, and
> bounds checking becomes possible on accesses to port_status and hostpc.

...

>         /* HOSTPC: offset 0x84 */
> -       u32             hostpc[0];      /* HOSTPC extension */
> +       u32             hostpc[HCS_N_PORTS_MAX];
>  #define HOSTPC_PHCD    (1<<22)         /* Phy clock disable */
>  #define HOSTPC_PSPD    (3<<25)         /* Port speed detection */
>
> -       u32             reserved5[17];
> +       u32             reserved5[2];

Shouldn't it be rather [17 - PORT_MAX]? for accuracy?
Or also a union approach?

-- 
With Best Regards,
Andy Shevchenko