Re: [Xen-devel] [PATCH V4 6/8] iommu/arm: Add lightweight iommu_fwspec support

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.09.2019 17:35, Oleksandr Tyshchenko wrote:
> --- /dev/null
> +++ b/xen/include/asm-arm/iommu_fwspec.h
> @@ -0,0 +1,68 @@
> +/*
> + * xen/include/asm-arm/iommu_fwspec.h
> + *
> + * Contains a common structure to hold the per-device firmware data and
> + * declaration of functions used to maintain that data
> + *
> + * Based on Linux's iommu_fwspec support you can find at:
> + *    include/linux/iommu.h
> + *
> + * Copyright (C) 2007-2008 Advanced Micro Devices, Inc.
> + *
> + * Copyright (C) 2019 EPAM Systems Inc.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms and conditions of the GNU General Public
> + * License, version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public
> + * License along with this program; If not, see 
> <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef __ARCH_ARM_IOMMU_FWSPEC_H__
> +#define __ARCH_ARM_IOMMU_FWSPEC_H__
> +
> +/* per-device IOMMU instance data */
> +struct iommu_fwspec {
> +    /* this device's IOMMU */
> +    struct device *iommu_dev;
> +    /* IOMMU driver private data for this device */
> +    void *iommu_priv;
> +    /* number of associated device IDs */
> +    unsigned int num_ids;
> +    /* IDs which this device may present to the IOMMU */
> +    uint32_t ids[1];
> +};

Note that you abuse xrealloc_flex_struct() when using it with such
a type: The last field is _not_ a flexible array member. Compilers
might legitimately warn if they can prove that you access
p->ids[1] anywhere, despite you (presumably) having allocated enough
space. (I haven't been able to think of a way for the macro to
actually detect and hence refuse such wrong uses.)

Jan

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