On Thu, Apr 27, 2023 at 05:10:06PM -0400, 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-jva6w38lk4hjowae5kcknhprd5fp...@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 > Resolves: CVE-2023-0330 > > Signed-off-by: Alexander Bulekov <alx...@bu.edu> > Reviewed-by: Thomas Huth <th...@redhat.com> > --- > include/exec/memory.h | 5 +++++ > include/hw/qdev-core.h | 7 +++++++ > softmmu/memory.c | 16 ++++++++++++++++ > 3 files changed, 28 insertions(+) > > diff --git a/include/exec/memory.h b/include/exec/memory.h > index 15ade918ba..e45ce6061f 100644 > --- a/include/exec/memory.h > +++ b/include/exec/memory.h > @@ -767,6 +767,8 @@ struct MemoryRegion { > bool is_iommu; > RAMBlock *ram_block; > Object *owner; > + /* owner as TYPE_DEVICE. Used for re-entrancy checks in MR access > hotpath */ > + DeviceState *dev; > > const MemoryRegionOps *ops; > void *opaque; > @@ -791,6 +793,9 @@ struct MemoryRegion { > unsigned ioeventfd_nb; > MemoryRegionIoeventfd *ioeventfds; > RamDiscardManager *rdm; /* Only for RAM */ > + > + /* For devices designed to perform re-entrant IO into their own IO MRs */ > + bool disable_reentrancy_guard; > }; > > struct IOMMUMemoryRegion { > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h > index bd50ad5ee1..7623703943 100644 > --- a/include/hw/qdev-core.h > +++ b/include/hw/qdev-core.h > @@ -162,6 +162,10 @@ struct NamedClockList { > QLIST_ENTRY(NamedClockList) node; > }; > > +typedef struct { > + bool engaged_in_io; > +} MemReentrancyGuard; > + > /** > * DeviceState: > * @realized: Indicates whether the device has been fully constructed. > @@ -194,6 +198,9 @@ struct DeviceState { > int alias_required_for_version; > ResettableState reset; > GSList *unplug_blockers; > + > + /* Is the device currently in mmio/pio/dma? Used to prevent re-entrancy > */ > + MemReentrancyGuard mem_reentrancy_guard; > }; > > struct DeviceListener { > diff --git a/softmmu/memory.c b/softmmu/memory.c > index b1a6cae6f5..fe23f0e5ce 100644 > --- a/softmmu/memory.c > +++ b/softmmu/memory.c > @@ -542,6 +542,18 @@ static MemTxResult access_with_adjusted_size(hwaddr addr, > access_size_max = 4; > } > > + /* Do not allow more than one simultaneous access to a device's IO > Regions */ > + if (mr->dev && !mr->disable_reentrancy_guard && > + !mr->ram_device && !mr->ram && !mr->rom_device && !mr->readonly) { > + if (mr->dev->mem_reentrancy_guard.engaged_in_io) { > + warn_report("Blocked re-entrant IO on " > + "MemoryRegion: %s at addr: 0x%" HWADDR_PRIX, > + memory_region_name(mr), addr); > + return MEMTX_ACCESS_ERROR;
If we issue this warn_report on every invalid memory access, is this going to become a denial of service by flooding logs, or is the return MEMTX_ACCESS_ERROR, sufficient to ensure this is only printed *once* in the lifetime of the QEMU process ? With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|