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

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>, Al Cooper <alcooperx@gmail.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	linux-usb@vger.kernel.org,
	Florian Fainelli <f.fainelli@gmail.com>,
	linux-kernel@vger.kernel.org,
	bcm-kernel-feedback-list@broadcom.com,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH 1/2] USB: EHCI: Add register array bounds to HCS ports
Date: Wed, 18 Aug 2021 12:48:17 +0300	[thread overview]
Message-ID: <CAHp75VdE3akTqmJ6VE4+Q4F959JscvZpiJok4=2JmjDjubtuxw@mail.gmail.com> (raw)
In-Reply-To: <20210818043035.1308062-2-keescook@chromium.org>

On Wed, Aug 18, 2021 at 7:30 AM Kees Cook <keescook@chromium.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