[PATCH v2] softmmu: Use memmove in flatview_write_continue

[PATCH v2] softmmu: Use memmove in flatview_write_continue

[Akihiko Odaki]

We found a case where the source passed to flatview_write_continue() may
overlap with the destination when fuzzing igb, a new proposed network
device with sanitizers.

igb uses pci_dma_map() to get Tx packet, and pci_dma_write() to write Rx
buffer. While pci_dma_write() is usually used to write data from
memory not mapped to the guest, if igb is configured to perform
loopback, the data will be sourced from the guest memory. The source and
destination can overlap and the usage of memcpy() will be invalid in
such a case.

While we do not really have to deal with such an invalid request for
igb, detecting the overlap in igb code beforehand requires complex code,
and only covers this specific case. Instead, just replace memcpy() with
memmove() to tolerate overlaps. Using memmove() will slightly damage the
performance as it will need to check overlaps before using SIMD
instructions for copying, but the cost should be negligible, considering
the inherent complexity of flatview_write_continue().

The test cases generated by the fuzzer is available at:
https://patchew.org/QEMU/20230129053316.1071513-1-alxndr@bu.edu/

The fixed test case is:
fuzz/crash_47dfe62d9f911bf523ff48cd441b61c0013ed805

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Acked-by: Alexander Bulekov <alxndr@bu.edu>
---
V1 -> V2: Correct spellings in the message

 softmmu/physmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index cb998cdf23..3cd27b1c9d 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -2828,7 +2828,7 @@ static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
         } else {
             /* RAM case */
             ram_ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
-            memcpy(ram_ptr, buf, l);
+            memmove(ram_ptr, buf, l);
             invalidate_and_set_dirty(mr, addr1, l);
         }
 
-- 
2.39.1

Re: [PATCH v2] softmmu: Use memmove in flatview_write_continue

[David Hildenbrand]

On 31.01.23 04:01, Akihiko Odaki wrote:
> We found a case where the source passed to flatview_write_continue() may
> overlap with the destination when fuzzing igb, a new proposed network
> device with sanitizers.
> 
> igb uses pci_dma_map() to get Tx packet, and pci_dma_write() to write Rx
> buffer. While pci_dma_write() is usually used to write data from
> memory not mapped to the guest, if igb is configured to perform
> loopback, the data will be sourced from the guest memory. The source and
> destination can overlap and the usage of memcpy() will be invalid in
> such a case.
> 
> While we do not really have to deal with such an invalid request for
> igb, detecting the overlap in igb code beforehand requires complex code,
> and only covers this specific case. Instead, just replace memcpy() with
> memmove() to tolerate overlaps. Using memmove() will slightly damage the
> performance as it will need to check overlaps before using SIMD
> instructions for copying, but the cost should be negligible, considering
> the inherent complexity of flatview_write_continue().
> 
> The test cases generated by the fuzzer is available at:
> https://patchew.org/QEMU/20230129053316.1071513-1-alxndr@bu.edu/
> 
> The fixed test case is:
> fuzz/crash_47dfe62d9f911bf523ff48cd441b61c0013ed805
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> Acked-by: Alexander Bulekov <alxndr@bu.edu>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb

Re: [PATCH v2] softmmu: Use memmove in flatview_write_continue

[Richard Henderson]

On 1/30/23 17:01, Akihiko Odaki wrote:
> We found a case where the source passed to flatview_write_continue() may
> overlap with the destination when fuzzing igb, a new proposed network
> device with sanitizers.
> 
> igb uses pci_dma_map() to get Tx packet, and pci_dma_write() to write Rx
> buffer. While pci_dma_write() is usually used to write data from
> memory not mapped to the guest, if igb is configured to perform
> loopback, the data will be sourced from the guest memory. The source and
> destination can overlap and the usage of memcpy() will be invalid in
> such a case.
> 
> While we do not really have to deal with such an invalid request for
> igb, detecting the overlap in igb code beforehand requires complex code,
> and only covers this specific case. Instead, just replace memcpy() with
> memmove() to tolerate overlaps. Using memmove() will slightly damage the
> performance as it will need to check overlaps before using SIMD
> instructions for copying, but the cost should be negligible, considering
> the inherent complexity of flatview_write_continue().
> 
> The test cases generated by the fuzzer is available at:
> https://patchew.org/QEMU/20230129053316.1071513-1-alxndr@bu.edu/
> 
> The fixed test case is:
> fuzz/crash_47dfe62d9f911bf523ff48cd441b61c0013ed805
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> Acked-by: Alexander Bulekov <alxndr@bu.edu>
> ---
> V1 -> V2: Correct spellings in the message

Queued to tcg-next.


r~

> 
>   softmmu/physmem.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
> index cb998cdf23..3cd27b1c9d 100644
> --- a/softmmu/physmem.c
> +++ b/softmmu/physmem.c
> @@ -2828,7 +2828,7 @@ static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
>           } else {
>               /* RAM case */
>               ram_ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
> -            memcpy(ram_ptr, buf, l);
> +            memmove(ram_ptr, buf, l);
>               invalidate_and_set_dirty(mr, addr1, l);
>           }
>