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
Resolves: CVE-2023-0330
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
include/exec/memory.h | 2 ++
include/hw/qdev-core.h | 7 +++++++
softmmu/memory.c | 14 ++++++++++++++
softmmu/trace-events | 1 +
4 files changed, 24 insertions(+)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 6fa0b071f0..6c0a5e68d3 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;
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 4699ba55ec..a11ee3e30d 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -542,6 +542,16 @@ 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) {
+ trace_memory_region_reentrant_io(get_cpu_index(), mr, addr, size);
+ 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 +566,9 @@ 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 +1183,7 @@ 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) {
diff --git a/softmmu/trace-events b/softmmu/trace-events
index 22606dc27b..62d04ea9a7 100644
--- a/softmmu/trace-events
+++ b/softmmu/trace-events
@@ -13,6 +13,7 @@ memory_region_ops_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, u
memory_region_ops_write(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size, const char *name) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u name '%s'"
memory_region_subpage_read(int cpu_index, void *mr, uint64_t offset, uint64_t value, unsigned size) "cpu %d mr %p offset 0x%"PRIx64" value 0x%"PRIx64" size %u"
memory_region_subpage_write(int cpu_index, void *mr, uint64_t offset, uint64_t value, unsigned size) "cpu %d mr %p offset 0x%"PRIx64" value 0x%"PRIx64" size %u"
+memory_region_reentrant_io(int cpu_index, void *mr, uint64_t offset, unsigned size) "cpu %d mr %p offset 0x%"PRIx64" size %u"
memory_region_ram_device_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u"
memory_region_ram_device_write(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u"
memory_region_sync_dirty(const char *mr, const char *listener, int global) "mr '%s' listener '%s' synced (global=%d)"
--
2.39.0