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Re: [PATCH] xen/evtchn: fix wrong usage of array_index_nospec()
- To: Juergen Gross <jgross@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 29 Jul 2026 16:22:55 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 29 Jul 2026 14:23:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29.07.2026 16:12, Juergen Gross wrote:
> --- a/xen/common/event_fifo.c
> +++ b/xen/common/event_fifo.c
> @@ -71,11 +71,10 @@ static inline event_word_t
> *evtchn_fifo_word_from_port(const struct domain *d,
> */
> smp_rmb();
>
> - p = array_index_nospec(port / EVTCHN_FIFO_EVENT_WORDS_PER_PAGE,
> - d->evtchn_fifo->num_evtchns);
> - w = port % EVTCHN_FIFO_EVENT_WORDS_PER_PAGE;
> + p = array_index_nospec(port, d->evtchn_fifo->num_evtchns);
> + w = p % EVTCHN_FIFO_EVENT_WORDS_PER_PAGE;
I don't see why the calculation of w would also need to change - whichever way
it is, w is bounded by EVTCHN_FIFO_EVENT_WORDS_PER_PAGE (and hence safe).
Preferably with that undone (can do while committing):
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
> - return d->evtchn_fifo->event_array[p] + w;
> + return d->evtchn_fifo->event_array[p / EVTCHN_FIFO_EVENT_WORDS_PER_PAGE]
> + w;
> }
>
> static void cf_check evtchn_fifo_init(struct domain *d, struct evtchn
> *evtchn)
|
