Re: [Qemu-devel] [PATCH v1 7/7] memory-device: rewrite address assignment using ranges

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* David Hildenbrand (david@redhat.com) wrote:
> Let's rewrite it properly using ranges. This fixes certain overflows that
> are right now possible. E.g.
> 
> qemu-system-x86_64 -m 4G,slots=20,maxmem=40G -M pc \
>     -object memory-backend-file,id=mem1,share,mem-path=/dev/zero,size=2G
>     -device pc-dimm,memdev=mem1,id=dimm1,addr=-0x40000000
> 
> Now properly reports an error instead of succeeding.
> 
> "can't add memory device [0xffffffffc0000000:0x80000000], range overflow"
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  hw/mem/memory-device.c | 56 +++++++++++++++++++++++++-----------------
>  1 file changed, 33 insertions(+), 23 deletions(-)
> 
> diff --git a/hw/mem/memory-device.c b/hw/mem/memory-device.c
> index 8be63c8032..1ca9c8e410 100644
> --- a/hw/mem/memory-device.c
> +++ b/hw/mem/memory-device.c
> @@ -100,9 +100,8 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
>                                              uint64_t align, uint64_t size,
>                                              Error **errp)
>  {
> -    uint64_t address_space_start, address_space_end;
>      GSList *list = NULL, *item;
> -    uint64_t new_addr = 0;
> +    Range as, new = range_empty;
>  
>      if (!ms->device_memory) {
>          error_setg(errp, "memory devices (e.g. for memory hotplug) are not "
> @@ -115,13 +114,11 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
>                           "enabled, please specify the maxmem option");
>          return 0;
>      }
> -    address_space_start = ms->device_memory->base;
> -    address_space_end = address_space_start +
> -                        memory_region_size(&ms->device_memory->mr);
> -    g_assert(address_space_end >= address_space_start);
> +    range_init(&as, ms->device_memory->base,
> +               memory_region_size(&ms->device_memory->mr));
>  
> -    /* address_space_start indicates the maximum alignment we expect */
> -    if (!QEMU_IS_ALIGNED(address_space_start, align)) {
> +    /* start of address space indicates the maximum alignment we expect */
> +    if (!QEMU_IS_ALIGNED(range_lob(&as), align)) {
>          error_setg(errp, "the alignment (0x%" PRIx64 ") is not supported",
>                     align);
>          return 0;
> @@ -145,20 +142,26 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
>      }
>  
>      if (hint) {
> -        new_addr = *hint;
> -        if (new_addr < address_space_start) {
> +        if (!range_valid(*hint, size)) {
>              error_setg(errp, "can't add memory device [0x%" PRIx64 ":0x%" PRIx64
> -                       "] before 0x%" PRIx64, new_addr, size,
> -                       address_space_start);
> +                       "], range overflow", *hint, size);
>              return 0;
> -        } else if ((new_addr + size) > address_space_end) {
> +        }
> +        range_init(&new, *hint, size);
> +        if (range_starts_before_range(&new, &as)) {
> +            error_setg(errp, "can't add memory device [0x%" PRIx64 ":0x%" PRIx64
> +                       "] before 0x%" PRIx64, range_lob(&new), range_size(&new),
> +                       range_lob(&as));
> +            return 0;
> +        } else if (range_ends_after_range(&new, &as)) {
>              error_setg(errp, "can't add memory device [0x%" PRIx64 ":0x%" PRIx64
> -                       "] beyond 0x%" PRIx64, new_addr, size,
> -                       address_space_end);
> +                       "] beyond 0x%" PRIx64, range_lob(&new), range_size(&new),
> +                       range_upb(&as));

Would !range_contains_range be easier here?

>              return 0;
>          }
>      } else {
> -        new_addr = address_space_start;
> +        /* our previous size checks make sure that this never overflows */

Hmm, which one exactly?

> +        range_init(&new, range_lob(&as), size);
>      }
>  
>      /* find address range that will fit new memory device */
> @@ -166,30 +169,37 @@ static uint64_t memory_device_get_free_addr(MachineState *ms,
>      for (item = list; item; item = g_slist_next(item)) {
>          const MemoryDeviceState *md = item->data;
>          const MemoryDeviceClass *mdc = MEMORY_DEVICE_GET_CLASS(OBJECT(md));
> -        uint64_t md_size, md_addr;
> +        uint64_t next_addr;
> +        Range tmp;
>  
> -        md_addr = mdc->get_addr(md);
> -        md_size = memory_device_get_region_size(md, &error_abort);
> +        range_init(&tmp, mdc->get_addr(md),
> +                   memory_device_get_region_size(md, &error_abort));
>  
> -        if (ranges_overlap(md_addr, md_size, new_addr, size)) {
> +        if (range_overlaps_range(&tmp, &new)) {
>              if (hint) {
>                  const DeviceState *d = DEVICE(md);
>                  error_setg(errp, "address range conflicts with memory device"
>                             " id='%s'", d->id ? d->id : "(unnamed)");
>                  goto out;
>              }
> -            new_addr = QEMU_ALIGN_UP(md_addr + md_size, align);
> +
> +            next_addr = QEMU_ALIGN_UP(range_upb(&tmp) + 1, align);
> +            if (!range_valid(next_addr, size)) {
> +                range_make_empty(&new);
> +                break;
> +            }
> +            range_init(&new, next_addr, size);
>          }
>      }
>  
> -    if (new_addr + size > address_space_end) {
> +    if (!range_contains_range(&as, &new)) {
>          error_setg(errp, "could not find position in guest address space for "
>                     "memory device - memory fragmented due to alignments");
>          goto out;
>      }
>  out:
>      g_slist_free(list);
> -    return new_addr;
> +    return range_lob(&new);
>  }
>  
>  MemoryDeviceInfoList *qmp_memory_device_list(void)
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK