On Wed, 21 Aug 2024 15:25:18 +0200 Igor Mammedov <imamm...@redhat.com> wrote:
> On Thu, 27 Apr 2023 17:10:06 -0400 > Alexander Bulekov <alx...@bu.edu> 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 > > Alexander, with 9.0 > we are getting > > warning: Blocked re-entrant IO on MemoryRegion: acpi-cpu-hotplug at addr: > 0x0 > > during CPU hot-unplug, to my knowledge there shouldn't be any DMA involved > there. > The only access should be either from guest kernel or firmware(this one is > under SMM mode)). > > Question is how this could happen on MMIO access which should be guarded by > BQL? For prosperity, reproducer (RHEL9.4 Haswell host + upstream QEMU/edk https://issues.redhat.com/browse/RHEL-56154): ./qemu-system-x86_64 --enable-kvm -smp 2,maxcpus=24,cores=12,threads=1,dies=1,sockets=2 \ -cpu host \ -blockdev '{"node-name": "file_ovmf_code", "driver": "file", "filename": "/tmp/qemu_build/pc-bios/edk2-x86_64-secure-code.fd", "auto-read-only": true, "discard": "unmap"}' \ -blockdev '{"node-name": "drive_ovmf_code", "driver": "raw", "read-only": true, "file": "file_ovmf_code"}' \ -blockdev '{"node-name": "file_ovmf_vars", "driver": "file", "filename": "/tmp/edk_VARS.raw", "auto-read-only": true, "discard": "unmap"}' \ -blockdev '{"node-name": "drive_ovmf_vars", "driver": "raw", "read-only": false, "file": "file_ovmf_vars"}' \ -M q35,pflash0=drive_ovmf_code,pflash1=drive_ovmf_vars \ -m 4G \ -monitor stdio \ rhel9.5.raw once booted (qemu) device_add host-x86_64-cpu,id=vcpu1,socket-id=1,core-id=10,die-id=0,thread-id=0 (qemu) device_add host-x86_64-cpu,id=vcpu2,socket-id=1,core-id=11,die-id=0,thread-id=0 (qemu) device_del vcpu1 (qemu) qemu-system-x86_64: warning: Blocked re-entrant IO on MemoryRegion: acpi-cpu-hotplug at addr: 0x0 > And where to start digging to find out if it's a genuine issue, > or whether it's safe to use big hammer and disable reentrancy guard? I'm hesitant to use hammer so far (though it would make problem nop). What happens is that cpu_remove_sync() temporarily releases BQL which lets conflicting access to happen. But I think unexpected access shouldn't be there in the 1st place, so guard looks pretty legit at this point. Lets see what Gerd finds out from edk2 point of view. > > > > 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; > > + } > > + mr->dev->mem_reentrancy_guard.engaged_in_io = true; > > + } > > + > > /* FIXME: support unaligned access? */ > > access_size = MAX(MIN(size, access_size_max), access_size_min); > > access_mask = MAKE_64BIT_MASK(0, access_size * 8); > > @@ -556,6 +568,9 @@ static MemTxResult access_with_adjusted_size(hwaddr > > addr, > > access_mask, attrs); > > } > > } > > + if (mr->dev) { > > + mr->dev->mem_reentrancy_guard.engaged_in_io = false; > > + } > > return r; > > } > > > > @@ -1170,6 +1185,7 @@ static void memory_region_do_init(MemoryRegion *mr, > > } > > mr->name = g_strdup(name); > > mr->owner = owner; > > + mr->dev = (DeviceState *) object_dynamic_cast(mr->owner, TYPE_DEVICE); > > mr->ram_block = NULL; > > > > if (name) { >
