Re: [PATCH v2] kvm: mpic: limit active IRQ sources to NUM_OUTPUTS

[Paul Mackerras <paulus@ozlabs.org>]

On Fri, Nov 15, 2019 at 10:36:20AM +0530, P J P wrote:
> From: P J P <pjp@fedoraproject.org>
> 
> openpic_src_write sets interrupt level 'src->output' masked with
> ILR_INTTGT_MASK(=0xFF). It's then used to index 'dst->outputs_active'
> array. With NUM_OUTPUTS=3, it may lead to OOB array access. Limit
> active IRQ sources to < NUM_OUTPUTS.
> 
> Reported-by: Reno Robert <renorobert@gmail.com>
> Signed-off-by: P J P <pjp@fedoraproject.org>
> ---
>  arch/powerpc/kvm/mpic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Update v2: limit IRQ sources to NUM_OUTPUTS
>   -> https://www.spinics.net/lists/kvm-ppc/msg16554.html
> 
> diff --git a/arch/powerpc/kvm/mpic.c b/arch/powerpc/kvm/mpic.c
> index fe312c160d97..fe4afd54c6e7 100644
> --- a/arch/powerpc/kvm/mpic.c
> +++ b/arch/powerpc/kvm/mpic.c
> @@ -628,7 +628,7 @@ static inline void write_IRQreg_ilr(struct openpic *opp, int n_IRQ,
>  	if (opp->flags & OPENPIC_FLAG_ILR) {
>  		struct irq_source *src = &opp->src[n_IRQ];
> 
> -		src->output = val & ILR_INTTGT_MASK;
> +		src->output = val % NUM_OUTPUTS;

Still not right, I'm afraid, since it could leave src->output set to
3, which would lead to an out-of-bounds array access.  I think it
needs to be

	if (val < NUM_OUTPUTS)
		src->output = val;
	else
		src->output = ILR_INTTGT_INT;

or something like that.

Paul.