Re: [PATCH] irqchip/gic-v3-its: Fix potential race condition in its_vlpi_prop_update()

[Marc Zyngier]

Hi Hagar,

On Thu, 30 May 2024 11:57:13 +0100,
Hagar Hemdan <hagarhem@xxxxxxxxxx> wrote:
> 
> Similar to commit 046b5054f566 ("irqchip/gic-v3-its: Lock VLPI map array
> before translating it"), its_vlpi_prop_update() calls lpi_write_config()
> which obtains the mapping information for a VLPI.
> This should always be done with vlpi_lock for this device held. Otherwise,
> its_vlpi_prop_update() could race with its_vlpi_unmap().

Thanks for reporting this. Note that this issue is not the same as the
one you refer to (what you have here is a total absence of locking,
while 046b5054f566 fixed a call to get_vlpi_map() outside of an
existing critical section).

> 
> This bug was discovered and resolved using Coverity Static Analysis
> Security Testing (SAST) by Synopsys, Inc.

Should we get a scrolling banner for this kind of advertisements? ;-)

> 
> Fixes: 015ec0386ab6 ("irqchip/gic-v3-its: Add VLPI configuration handling")
> Signed-off-by: Hagar Hemdan <hagarhem@xxxxxxxxxx>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 40ebf1726393..ecaad1786345 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -1970,9 +1970,13 @@ static int its_vlpi_unmap(struct irq_data *d)
>  static int its_vlpi_prop_update(struct irq_data *d, struct its_cmd_info *info)
>  {
>  	struct its_device *its_dev = irq_data_get_irq_chip_data(d);
> +	int ret = 0;
>  
> -	if (!its_dev->event_map.vm || !irqd_is_forwarded_to_vcpu(d))
> -		return -EINVAL;
> +	raw_spin_lock(&its_dev->event_map.vlpi_lock);
> +	if (!its_dev->event_map.vm || !irqd_is_forwarded_to_vcpu(d)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
>  
>  	if (info->cmd_type == PROP_UPDATE_AND_INV_VLPI)
>  		lpi_update_config(d, 0xff, info->config);
> @@ -1980,7 +1984,9 @@ static int its_vlpi_prop_update(struct irq_data *d, struct its_cmd_info *info)
>  		lpi_write_config(d, 0xff, info->config);
>  	its_vlpi_set_doorbell(d, !!(info->config & LPI_PROP_ENABLED));
>  
> -	return 0;
> +out:
> +	raw_spin_unlock(&its_dev->event_map.vlpi_lock);
> +	return ret;
>  }
>  
>  static int its_irq_set_vcpu_affinity(struct irq_data *d, void *vcpu_info)

As it turns out, all the calls from its_irq_set_vcpu_affinity()
require the same lock to be held. So instead of peppering the locking
all over the place, we could (should?) hoist the locking into
its_irq_set_vcpu_affinity() and avoid future bugs. It also results in
a negative diffstat.

Something like the hack below (compile-tested only), which I'm sure
the "Coverity Static Analysis Security Testing (SAST) by Synopsys,
Inc" will be able to verify...

	M.

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 40ebf1726393..abc1fb360ce4 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -1851,23 +1851,18 @@ static int its_vlpi_map(struct irq_data *d, struct its_cmd_info *info)
 	if (!info->map)
 		return -EINVAL;
 
-	raw_spin_lock(&its_dev->event_map.vlpi_lock);
-
 	if (!its_dev->event_map.vm) {
 		struct its_vlpi_map *maps;
 
 		maps = kcalloc(its_dev->event_map.nr_lpis, sizeof(*maps),
 			       GFP_ATOMIC);
-		if (!maps) {
-			ret = -ENOMEM;
-			goto out;
-		}
+		if (!maps)
+			return -ENOMEM;
 
 		its_dev->event_map.vm = info->map->vm;
 		its_dev->event_map.vlpi_maps = maps;
 	} else if (its_dev->event_map.vm != info->map->vm) {
-		ret = -EINVAL;
-		goto out;
+		return -EINVAL;
 	}
 
 	/* Get our private copy of the mapping information */
@@ -1899,8 +1894,6 @@ static int its_vlpi_map(struct irq_data *d, struct its_cmd_info *info)
 		its_dev->event_map.nr_vlpis++;
 	}
 
-out:
-	raw_spin_unlock(&its_dev->event_map.vlpi_lock);
 	return ret;
 }
 
@@ -1910,20 +1903,14 @@ static int its_vlpi_get(struct irq_data *d, struct its_cmd_info *info)
 	struct its_vlpi_map *map;
 	int ret = 0;
 
-	raw_spin_lock(&its_dev->event_map.vlpi_lock);
-
 	map = get_vlpi_map(d);
 
-	if (!its_dev->event_map.vm || !map) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (!its_dev->event_map.vm || !map)
+		return -EINVAL;
 
 	/* Copy our mapping information to the incoming request */
 	*info->map = *map;
 
-out:
-	raw_spin_unlock(&its_dev->event_map.vlpi_lock);
 	return ret;
 }
 
@@ -1933,12 +1920,8 @@ static int its_vlpi_unmap(struct irq_data *d)
 	u32 event = its_get_event_id(d);
 	int ret = 0;
 
-	raw_spin_lock(&its_dev->event_map.vlpi_lock);
-
-	if (!its_dev->event_map.vm || !irqd_is_forwarded_to_vcpu(d)) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (!its_dev->event_map.vm || !irqd_is_forwarded_to_vcpu(d))
+		return -EINVAL;
 
 	/* Drop the virtual mapping */
 	its_send_discard(its_dev, event);
@@ -1962,8 +1945,6 @@ static int its_vlpi_unmap(struct irq_data *d)
 		kfree(its_dev->event_map.vlpi_maps);
 	}
 
-out:
-	raw_spin_unlock(&its_dev->event_map.vlpi_lock);
 	return ret;
 }
 
@@ -1987,29 +1968,41 @@ static int its_irq_set_vcpu_affinity(struct irq_data *d, void *vcpu_info)
 {
 	struct its_device *its_dev = irq_data_get_irq_chip_data(d);
 	struct its_cmd_info *info = vcpu_info;
+	int ret;
 
 	/* Need a v4 ITS */
 	if (!is_v4(its_dev->its))
 		return -EINVAL;
 
+	raw_spin_lock(&its_dev->event_map.vlpi_lock);
+
 	/* Unmap request? */
-	if (!info)
-		return its_vlpi_unmap(d);
+	if (!info) {
+		ret = its_vlpi_unmap(d);
+		goto out;
+	}
 
 	switch (info->cmd_type) {
 	case MAP_VLPI:
-		return its_vlpi_map(d, info);
+		ret = its_vlpi_map(d, info);
+		break;
 
 	case GET_VLPI:
-		return its_vlpi_get(d, info);
+		ret = its_vlpi_get(d, info);
+		break;
 
 	case PROP_UPDATE_VLPI:
 	case PROP_UPDATE_AND_INV_VLPI:
-		return its_vlpi_prop_update(d, info);
+		ret = its_vlpi_prop_update(d, info);
+		break;
 
 	default:
-		return -EINVAL;
+		ret = -EINVAL;
 	}
+
+out:
+	raw_spin_unlock(&its_dev->event_map.vlpi_lock);
+	return ret;
 }
 
 static struct irq_chip its_irq_chip = {

-- 
Without deviation from the norm, progress is not possible.