linux-kernel - Re: [PATCH] firmware: xilinx: fix out-of-bounds access

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Date:   Tue, 27 Oct 2020 10:53:11 +0100
From:   Michal Simek <michal.simek@...inx.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Michal Simek <michal.simek@...inx.com>,
        Rajan Vaja <rajanv@...inx.com>
CC:     Arnd Bergmann <arnd@...db.de>, Rajan Vaja <rajan.vaja@...inx.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Tejas Patel <tejas.patel@...inx.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, git <git@...inx.com>
Subject: Re: [PATCH] firmware: xilinx: fix out-of-bounds access



On 26. 10. 20 16:54, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The zynqmp_pm_set_suspend_mode() and zynqmp_pm_get_trustzone_version()
> functions pass values as api_id into zynqmp_pm_invoke_fn
> that are beyond PM_API_MAX, resulting in an out-of-bounds access:
> 
> drivers/firmware/xilinx/zynqmp.c: In function 'zynqmp_pm_set_suspend_mode':
> drivers/firmware/xilinx/zynqmp.c:150:24: warning: array subscript 2562 is above array bounds of 'u32[64]' {aka 'unsigned int[64]'} [-Warray-bounds]
>   150 |  if (zynqmp_pm_features[api_id] != PM_FEATURE_UNCHECKED)
>       |      ~~~~~~~~~~~~~~~~~~^~~~~~~~
> drivers/firmware/xilinx/zynqmp.c:28:12: note: while referencing 'zynqmp_pm_features'
>    28 | static u32 zynqmp_pm_features[PM_API_MAX];
>       |            ^~~~~~~~~~~~~~~~~~

Which CONFIG option/tool is reporting this issue?

> 
> Replace the resulting undefined behavior with an error return.
> This may break some things that happen to work at the moment
> but seems better than randomly overwriting kernel data.
> 
> I assume we need additional fixes for the two functions that now
> return an error.
> 
> Fixes: 76582671eb5d ("firmware: xilinx: Add Zynqmp firmware driver")
> Fixes: e178df31cf41 ("firmware: xilinx: Implement ZynqMP power management APIs")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/firmware/xilinx/zynqmp.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/firmware/xilinx/zynqmp.c b/drivers/firmware/xilinx/zynqmp.c
> index 8d1ff2454e2e..efb8a66efc68 100644
> --- a/drivers/firmware/xilinx/zynqmp.c
> +++ b/drivers/firmware/xilinx/zynqmp.c
> @@ -147,6 +147,9 @@ static int zynqmp_pm_feature(u32 api_id)
>  		return 0;
>  
>  	/* Return value if feature is already checked */
> +	if (api_id > ARRAY_SIZE(zynqmp_pm_features))
> +		return PM_FEATURE_INVALID;
> +
>  	if (zynqmp_pm_features[api_id] != PM_FEATURE_UNCHECKED)
>  		return zynqmp_pm_features[api_id];
>  
> 

Definitely good catch but not quite sure what should be correct reaction.
Rajan: Can you please take a look at it with priority?

Thanks,
Michal