Re: [PATCH] KVM: arm64: its: Fix missing dynamic allocation check in scan_its_table

[Marc Zyngier <marc.zyngier@arm.com>]

On 13/10/17 11:52, Christoffer Dall wrote:
> We currently allocate an entry dynamically, but we never check if the
> allocation actually succeeded.  We actually don't need a dynamic
> allocation, because we know the maximum size of an ITS table entry, so
> we can simply use an allocation on the stack.
> 
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index f51c1e1..555f42f 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -176,6 +176,7 @@ static const struct vgic_its_abi its_table_abi_versions[] = {
>  };
>  
>  #define NR_ITS_ABIS	ARRAY_SIZE(its_table_abi_versions)
> +#define MAX_ENTRY_SIZE	8	/* Max Entry size across all ABI versions */
>  
>  inline const struct vgic_its_abi *vgic_its_get_abi(struct vgic_its *its)
>  {
> @@ -1801,37 +1802,33 @@ typedef int (*entry_fn_t)(struct vgic_its *its, u32 id, void *entry,
>  static int scan_its_table(struct vgic_its *its, gpa_t base, int size, int esz,
>  			  int start_id, entry_fn_t fn, void *opaque)
>  {
> -	void *entry = kzalloc(esz, GFP_KERNEL);
>  	struct kvm *kvm = its->dev->kvm;
>  	unsigned long len = size;
>  	int id = start_id;
>  	gpa_t gpa = base;
> +	char entry[MAX_ENTRY_SIZE];

Nit: you can drop the memset below if you initialize immediately, and
GCC supporting dynamic arrays allows you to write this:

	char entry[esz] = { 0, };

so that you don't have to add the MAX_ENTRY_SIZE.

>  	int ret;
>  
> +	memset(entry, 0, MAX_ENTRY_SIZE);
> +
>  	while (len > 0) {
>  		int next_offset;
>  		size_t byte_offset;
>  
>  		ret = kvm_read_guest(kvm, gpa, entry, esz);
>  		if (ret)
> -			goto out;
> +			return ret;
>  
>  		next_offset = fn(its, id, entry, opaque);
> -		if (next_offset <= 0) {
> -			ret = next_offset;
> -			goto out;
> -		}
> +		if (next_offset <= 0)
> +			return next_offset;
>  
>  		byte_offset = next_offset * esz;
>  		id += next_offset;
>  		gpa += byte_offset;
>  		len -= byte_offset;
>  	}
> -	ret =  1;
> -
> -out:
> -	kfree(entry);
> -	return ret;
> +	return 1;
>  }
>  
>  /**
> 

Otherwise:

Acked-by: Marc Zyngier <marc.zyngier@arm.com>

	M.
-- 
Jazz is not dead. It just smells funny...