[PATCH] ARM: kernel: fix nr_cpu_ids check in DT logical map init

[lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)]

Hi Russell,

On Wed, Nov 21, 2012 at 04:42:56PM +0000, Lorenzo Pieralisi wrote:
> If a kernel is configured with a DT containing more /cpu nodes than
> nr_cpu_ids, the number of cpus must be capped in the DT parsing
> code. Current code carries out the check, but fails to cap the
> value and the check is executed after the cpu logical index is used,
> which can lead to memory corruption due to index overflow.
> 
> This patch refactors the check against nr_cpu_ids and move it before
> any computed index is used in the parsing code.
> 
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Reported-by: Mark Rutland <mark.rutland@arm.com>
> ---
> Russell,
> 
> while refactoring the DT loop over nodes, I unfortunately missed this niggle
> in the parsing loop that Mark reported. Here is the fix, sorry for the
> additional commit, if it is ok for you I will add it to your patch system.
> 
> Apologies and thanks,
> Lorenzo
> 
>  arch/arm/kernel/devtree.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
> index aaf9add..70f1bde 100644
> --- a/arch/arm/kernel/devtree.c
> +++ b/arch/arm/kernel/devtree.c
> @@ -139,10 +139,14 @@ void __init arm_dt_init_cpu_maps(void)
>  			i = cpuidx++;
>  		}
>  
> -		tmp_map[i] = hwid;
> -
> -		if (cpuidx > nr_cpu_ids)
> +		if (WARN(cpuidx > nr_cpu_ids, "DT /cpu %u nodes greater than "
> +					       "max cores %u, capping them\n",
> +					       cpuidx, nr_cpu_ids)) {
> +			cpuidx = nr_cpu_ids;
>  			break;
> +		}
> +
> +		tmp_map[i] = hwid;
>  	}
>  
>  	if (WARN(!bootcpu_valid, "DT missing boot CPU MPIDR[23:0], "

If it looks fine to you, can I queue this simple fix in your patch
system please ?

Thanks and apologies for the extra commit,
Lorenzo