Re: [PATCH] memory: stricter checks prior to unsetting engaged_in_io

[Darren Kenny <darren.kenny@oracle.com>]

On Tuesday, 2023-05-16 at 04:40:02 -04, Alexander Bulekov wrote:
> engaged_in_io could be unset by an MR with re-entrancy checks disabled.
> Ensure that only MRs that can set the engaged_in_io flag can unset it.
>
> Closes: https://gitlab.com/qemu-project/qemu/-/issues/1563
> Reported-by: Thomas Huth <thuth@redhat.com>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

> ---
>  softmmu/memory.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index b7b3386e9d..26424f1d78 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -534,6 +534,7 @@ static MemTxResult access_with_adjusted_size(hwaddr addr,
>      unsigned access_size;
>      unsigned i;
>      MemTxResult r = MEMTX_OK;
> +    bool reentrancy_guard_applied = false;
>  
>      if (!access_size_min) {
>          access_size_min = 1;
> @@ -552,6 +553,7 @@ static MemTxResult access_with_adjusted_size(hwaddr addr,
>              return MEMTX_ACCESS_ERROR;
>          }
>          mr->dev->mem_reentrancy_guard.engaged_in_io = true;
> +        reentrancy_guard_applied = true;
>      }
>  
>      /* FIXME: support unaligned access? */
> @@ -568,7 +570,7 @@ static MemTxResult access_with_adjusted_size(hwaddr addr,
>                          access_mask, attrs);
>          }
>      }
> -    if (mr->dev) {
> +    if (mr->dev && reentrancy_guard_applied) {
>          mr->dev->mem_reentrancy_guard.engaged_in_io = false;
>      }
>      return r;
> -- 
> 2.39.0