Re: [PATCH v7 1/6] memory: prevent dma-reentracy issues

[Philippe Mathieu-Daudé]

On 13/3/23 09:24, Alexander Bulekov wrote:
> Add a flag to the DeviceState, when a device is engaged in PIO/MMIO/DMA.
> This flag is set/checked prior to calling a device's MemoryRegion
> handlers, and set when device code initiates DMA.  The purpose of this
> flag is to prevent two types of DMA-based reentrancy issues:
>
> 1.) mmio -> dma -> mmio case
> 2.) bh -> dma write -> mmio case
>
> These issues have led to problems such as stack-exhaustion and
> use-after-frees.
>
> Summary of the problem from Peter Maydell:
> https://lore.kernel.org/qemu-devel/CAFEAcA_23vc7hE3iaM-JVA6W38LK4hJoWae5KcknhPRD5fPBZA@mail.gmail.com
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/62
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/540
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/541
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/556
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/557
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/827
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1282

BTW we need to commit these reproducers as tests/qtest/fuzz-*.

> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> Acked-by: Peter Xu <peterx@redhat.com>
> ---
>   include/hw/qdev-core.h |  7 +++++++
>   softmmu/memory.c       | 17 +++++++++++++++++
>   softmmu/trace-events   |  1 +
>   3 files changed, 25 insertions(+)