Re: [PATCH v7 14/17] vfio-user: handle PCI BAR accesses

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Fri, Mar 25, 2022 at 03:19:43PM -0400, Jagannathan Raman wrote:
> @@ -324,6 +325,170 @@ static void dma_unregister(vfu_ctx_t *vfu_ctx, vfu_dma_info_t *info)
>      trace_vfu_dma_unregister((uint64_t)info->iova.iov_base);
>  }
>  
> +static size_t vfu_object_bar_rw(PCIDevice *pci_dev, int pci_bar,
> +                                hwaddr offset, char * const buf,
> +                                hwaddr len, const bool is_write)
> +{
> +    uint8_t *ptr = (uint8_t *)buf;
> +    uint8_t *ram_ptr = NULL;
> +    bool release_lock = false;
> +    MemoryRegionSection section = { 0 };
> +    MemoryRegion *mr = NULL;
> +    int access_size;
> +    hwaddr size = 0;
> +    MemTxResult result;
> +    uint64_t val;
> +
> +    section = memory_region_find(pci_dev->io_regions[pci_bar].memory,
> +                                 offset, len);
> +
> +    if (!section.mr) {
> +        return 0;
> +    }
> +
> +    mr = section.mr;
> +    offset = section.offset_within_region;
> +
> +    if (is_write && mr->readonly) {
> +        warn_report("vfu: attempting to write to readonly region in "
> +                    "bar %d - [0x%"PRIx64" - 0x%"PRIx64"]",
> +                    pci_bar, offset, (offset + len));
> +        return 0;

A mr reference is leaked. The return statement can be replaced with goto
exit.

> +    }
> +
> +    if (memory_access_is_direct(mr, is_write)) {
> +        /**
> +         * Some devices expose a PCI expansion ROM, which could be buffer
> +         * based as compared to other regions which are primarily based on
> +         * MemoryRegionOps. memory_region_find() would already check
> +         * for buffer overflow, we don't need to repeat it here.
> +         */
> +        ram_ptr = memory_region_get_ram_ptr(mr);
> +
> +        size = len;

This looks like it will access beyond the end of ram_ptr when
section.size < len after memory_region_find() returns.

> +
> +        if (is_write) {
> +            memcpy((ram_ptr + offset), buf, size);
> +        } else {
> +            memcpy(buf, (ram_ptr + offset), size);
> +        }
> +
> +        goto exit;

What happens when the access spans two adjacent MemoryRegions? I think
the while (len > 0) loop is needed even in the memory_access_is_direct()
case so we perform the full access instead of truncating it.

> +    }
> +
> +    while (len > 0) {

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