[Bug 1880355] Re: Length restrictions for fw_cfg_dma_transfer?

[Thomas Huth]

Ok, thanks for checking! Closing now.

** Changed in: qemu
       Status: Incomplete => Fix Released

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Title:
  Length restrictions for fw_cfg_dma_transfer?

Status in QEMU:
  Fix Released

Bug description:
  For me, this takes close to 3 minutes at 100% CPU:
  echo "outl 0x518 0x9596ffff" | ./i386-softmmu/qemu-system-i386 -M q35 -m 32 
-nographic -accel qtest -monitor none -serial none -qtest stdio

  #0  phys_page_find (d=0x606000035d80, addr=136728041144404) at /exec.c:338
  #1  address_space_lookup_region (d=0x606000035d80, addr=136728041144404, 
resolve_subpage=true) at /exec.c:363
  #2  address_space_translate_internal (d=0x606000035d80, addr=136728041144404, 
xlat=0x7fff1fc0d070, plen=0x7fff1fc0d090, resolve_subpage=true) at /exec.c:382
  #3  flatview_do_translate (fv=0x606000035d20, addr=136728041144404, 
xlat=0x7fff1fc0d070, plen_out=0x7fff1fc0d090, page_mask_out=0x0, is_write=true, 
is_mmio=true, target_as=0x7fff1fc0ce10, attrs=...)
      pment/qemu/exec.c:520
  #4  flatview_translate (fv=0x606000035d20, addr=136728041144404, 
xlat=0x7fff1fc0d070, plen=0x7fff1fc0d090, is_write=true, attrs=...) at 
/exec.c:586
  #5  flatview_write_continue (fv=0x606000035d20, addr=136728041144404, 
attrs=..., ptr=0x7fff1fc0d660, len=172, addr1=136728041144400, l=172, 
mr=0x557fd54e77e0 <io_mem_unassigned>)
      pment/qemu/exec.c:3160
  #6  flatview_write (fv=0x606000035d20, addr=136728041144064, attrs=..., 
buf=0x7fff1fc0d660, len=512) at /exec.c:3177
  #7  address_space_write (as=0x557fd54e7a00 <address_space_memory>, 
addr=136728041144064, attrs=..., buf=0x7fff1fc0d660, len=512) at /exec.c:3271
  #8  dma_memory_set (as=0x557fd54e7a00 <address_space_memory>, 
addr=136728041144064, c=0 '\000', len=1378422272) at /dma-helpers.c:31
  #9  fw_cfg_dma_transfer (s=0x61a000001e80) at /hw/nvram/fw_cfg.c:400
  #10 fw_cfg_dma_mem_write (opaque=0x61a000001e80, addr=4, value=4294940309, 
size=4) at /hw/nvram/fw_cfg.c:467
  #11 memory_region_write_accessor (mr=0x61a000002200, addr=4, 
value=0x7fff1fc0e3d0, size=4, shift=0, mask=4294967295, attrs=...) at 
/memory.c:483
  #12 access_with_adjusted_size (addr=4, value=0x7fff1fc0e3d0, size=4, 
access_size_min=1, access_size_max=8, access_fn=0x557fd2288c80 
<memory_region_write_accessor>, mr=0x61a000002200, attrs=...)
      pment/qemu/memory.c:539
  #13 memory_region_dispatch_write (mr=0x61a000002200, addr=4, data=4294940309, 
op=MO_32, attrs=...) at /memory.c:1476
  #14 flatview_write_continue (fv=0x606000035f00, addr=1304, attrs=..., 
ptr=0x7fff1fc0ec40, len=4, addr1=4, l=4, mr=0x61a000002200) at /exec.c:3137
  #15 flatview_write (fv=0x606000035f00, addr=1304, attrs=..., 
buf=0x7fff1fc0ec40, len=4) at /exec.c:3177
  #16 address_space_write (as=0x557fd54e7bc0 <address_space_io>, addr=1304, 
attrs=..., buf=0x7fff1fc0ec40, len=4) at /exec.c:3271

  
  It looks like fw_cfg_dma_transfer gets the address(136728041144064) and 
length(1378422272) for the read from the value provided as input 4294940309 
(0xFFFF9695) which lands in pcbios. Should there be any limits on the length of 
guest-memory that fw_cfg should populate?
  Found by libfuzzer

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