From: Alexander Bulekov <alxndr@bu.edu>
Date: Thu, 27 Apr 2023 17:10:06 -0400
Subject: memory: prevent dma-reentracy issues

Git-commit: a2e1753b8054344f32cf94f31c6399a58794a380
References: bsc#1190011 (CVE-2021-3750)

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>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230427211013.2994127-2-alxndr@bu.edu>
[thuth: Replace warn_report() with warn_report_once()]
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
---
 include/exec/memory.h  |  5 +++++
 include/hw/qdev-core.h |  7 +++++++
 memory.c               | 16 ++++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 2b8bccdd8c1e641f092fcc9d8517..0c8cdb8ea2b68d7ad3ebdca0bdfe 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -378,6 +378,8 @@ 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;
@@ -400,6 +402,9 @@ struct MemoryRegion {
     const char *name;
     unsigned ioeventfd_nb;
     MemoryRegionIoeventfd *ioeventfds;
+
+    /* 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 66d031683f461a5fa6b854057299..0c8087fd4b25d3b07889801f3725 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -140,6 +140,10 @@ struct NamedGPIOList {
     QLIST_ENTRY(NamedGPIOList) node;
 };
 
+typedef struct {
+    bool engaged_in_io;
+} MemReentrancyGuard;
+
 /**
  * DeviceState:
  * @realized: Indicates whether the device has been fully constructed.
@@ -167,6 +171,9 @@ struct DeviceState {
     int num_child_bus;
     int instance_id_alias;
     int alias_required_for_version;
+
+    /* Is the device currently in mmio/pio/dma? Used to prevent re-entrancy */
+    MemReentrancyGuard mem_reentrancy_guard;
 };
 
 struct DeviceListener {
diff --git a/memory.c b/memory.c
index 8cafb86a91b0d69a0b24658fa423..1e77ba68ce529ee59c4591aabf16 100644
--- a/memory.c
+++ b/memory.c
@@ -531,6 +531,18 @@ 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_once("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);
@@ -545,6 +557,9 @@ 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;
 }
 
@@ -1132,6 +1147,7 @@ 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) {
