[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v7 1/6] memory: prevent dma-reentracy issues
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH v7 1/6] memory: prevent dma-reentracy issues |
Date: |
Mon, 13 Mar 2023 09:45:39 +0100 |
User-agent: |
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 |
Hi Alex,
Sorry for the late review, *sigh*.
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
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(+)
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;
Do you plan to add more fields?
+} 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;
At this point I'm not sure anymore this is a device or MR property.
};
struct DeviceListener {
diff --git a/softmmu/memory.c b/softmmu/memory.c
index 4699ba55ec..57bf18a257 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -533,6 +533,7 @@ static MemTxResult access_with_adjusted_size(hwaddr addr,
uint64_t access_mask;
unsigned access_size;
unsigned i;
+ DeviceState *dev = NULL;
MemTxResult r = MEMTX_OK;
if (!access_size_min) {
@@ -542,6 +543,19 @@ static MemTxResult access_with_adjusted_size(hwaddr addr,
access_size_max = 4;
}
+ /* Do not allow more than one simultanous access to a device's IO Regions */
Typo "simultaneous".
1/ access_with_adjusted_size() is complex enough and we are having hard
time getting it right. I'd prefer we don't intermix size adjustment
and re-entrancy check in the same function. This check could belong
to the callers.
2/ I'm not keen on calling QOM object_dynamic_cast() in this hot path;
and mixing QDev API within MR one. At least, can we cache this value
once in memory_region_do_init() since we have access to @owner?
+ if (mr->owner &&
+ !mr->ram_device && !mr->ram && !mr->rom_device && !mr->readonly) {
+ dev = (DeviceState *) object_dynamic_cast(mr->owner, TYPE_DEVICE);
+ if (dev) {
+ if (dev->mem_reentrancy_guard.engaged_in_io) {
+ trace_memory_region_reentrant_io(get_cpu_index(), mr, addr,
size);
+ return MEMTX_ERROR;
MEMTX_ERROR is device-specific, I'm not sure it is right to return it
from this generic path. Maybe you meant MEMTX_ACCESS_ERROR?
+ }
+ 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 +570,9 @@ static MemTxResult access_with_adjusted_size(hwaddr addr,
access_mask, attrs);
}
}
+ if (dev) {
+ dev->mem_reentrancy_guard.engaged_in_io = false;
+ }
return r;
}
- [PATCH v7 0/6] memory: prevent dma-reentracy issues, Alexander Bulekov, 2023/03/13
- [PATCH v7 2/6] async: Add an optional reentrancy guard to the BH API, Alexander Bulekov, 2023/03/13
- [PATCH v7 3/6] checkpatch: add qemu_bh_new/aio_bh_new checks, Alexander Bulekov, 2023/03/13
- [PATCH v7 5/6] memory: Allow disabling re-entrancy checking per-MR, Alexander Bulekov, 2023/03/13
- [PATCH v7 4/6] hw: replace most qemu_bh_new calls with qemu_bh_new_guarded, Alexander Bulekov, 2023/03/13