linux-kernel - Re: [PATCH v2 04/10] KVM: arm/arm64: vgic-its: Check GITS

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Date:   Fri, 13 Oct 2017 15:24:57 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, marc.zyngier@....com,
        peter.maydell@...aro.org, andre.przywara@....com,
        wanghaibin.wang@...wei.com, wu.wubin@...wei.com
Subject: Re: [PATCH v2 04/10] KVM: arm/arm64: vgic-its: Check GITS_BASER
 Valid bit before saving tables

On Wed, Sep 27, 2017 at 03:28:34PM +0200, Eric Auger wrote:
> At the moment we don't properly check the GITS_BASER<n>.Valid
> bit before saving the collection and device tables.
> 
> On Collection table save() we use the gpa field whereas the Valid bit

'Collection table save()' looks weird. Just use the actual function name
when referring to logic in the code: vgic_its_save_collection_table().

> should be used. On device table save() there is no check. This can
> cause various bugs, among which a subsequent fault when accessing
> the table in guest memory.
> 
> Let's systematically check the Valid bit before doing anything.
> 
> We also unifomize the code between save and restore.

Otherwise:

Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>

> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index c1f7972..60ecf91 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -2067,11 +2067,12 @@ static int vgic_its_device_cmp(void *priv, struct list_head *a,
>  static int vgic_its_save_device_tables(struct vgic_its *its)
>  {
>  	const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> +	u64 baser = its->baser_device_table;
>  	struct its_device *dev;
>  	int dte_esz = abi->dte_esz;
> -	u64 baser;
>  
> -	baser = its->baser_device_table;
> +	if (!(baser & GITS_BASER_VALID))
> +		return 0;
>  
>  	list_sort(NULL, &its->device_list, vgic_its_device_cmp);
>  
> @@ -2217,17 +2218,17 @@ static int vgic_its_restore_cte(struct vgic_its *its, gpa_t gpa, int esz)
>  static int vgic_its_save_collection_table(struct vgic_its *its)
>  {
>  	const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> +	u64 baser = its->baser_coll_table;
> +	gpa_t gpa = BASER_ADDRESS(baser);
>  	struct its_collection *collection;
>  	u64 val;
> -	gpa_t gpa;
>  	size_t max_size, filled = 0;
>  	int ret, cte_esz = abi->cte_esz;
>  
> -	gpa = BASER_ADDRESS(its->baser_coll_table);
> -	if (!gpa)
> +	if (!(baser & GITS_BASER_VALID))
>  		return 0;
>  
> -	max_size = GITS_BASER_NR_PAGES(its->baser_coll_table) * SZ_64K;
> +	max_size = GITS_BASER_NR_PAGES(baser) * SZ_64K;
>  
>  	list_for_each_entry(collection, &its->collection_list, coll_list) {
>  		ret = vgic_its_save_cte(its, collection, gpa, cte_esz);
> @@ -2258,17 +2259,18 @@ static int vgic_its_save_collection_table(struct vgic_its *its)
>  static int vgic_its_restore_collection_table(struct vgic_its *its)
>  {
>  	const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> +	u64 baser = its->baser_coll_table;
>  	int cte_esz = abi->cte_esz;
>  	size_t max_size, read = 0;
>  	gpa_t gpa;
>  	int ret;
>  
> -	if (!(its->baser_coll_table & GITS_BASER_VALID))
> +	if (!(baser & GITS_BASER_VALID))
>  		return 0;
>  
> -	gpa = BASER_ADDRESS(its->baser_coll_table);
> +	gpa = BASER_ADDRESS(baser);
>  
> -	max_size = GITS_BASER_NR_PAGES(its->baser_coll_table) * SZ_64K;
> +	max_size = GITS_BASER_NR_PAGES(baser) * SZ_64K;
>  
>  	while (read < max_size) {
>  		ret = vgic_its_restore_cte(its, gpa, cte_esz);
> -- 
> 2.5.5
>