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[RFC PATCH-for-7.2 v3 4/5] hw/display/qxl: Avoid buffer overrun in qxl_p
From: |
Philippe Mathieu-Daudé |
Subject: |
[RFC PATCH-for-7.2 v3 4/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt (CVE-2022-4144) |
Date: |
Mon, 28 Nov 2022 21:27:40 +0100 |
Have qxl_get_check_slot_offset() return false if the requested
buffer size does not fit within the slot memory region.
Similarly qxl_phys2virt() now returns NULL in such case, and
qxl_dirty_one_surface() aborts.
This avoids buffer overrun in the host pointer returned by
memory_region_get_ram_ptr().
Fixes: CVE-2022-4144 (out-of-bounds read)
Reported-by: Wenxu Yin (@awxylitol)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1336
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
hw/display/qxl.c | 27 +++++++++++++++++++++++----
hw/display/qxl.h | 2 +-
2 files changed, 24 insertions(+), 5 deletions(-)
diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 231d733250..0b21626aad 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -1424,11 +1424,13 @@ static void qxl_reset_surfaces(PCIQXLDevice *d)
/* can be also called from spice server thread context */
static bool qxl_get_check_slot_offset(PCIQXLDevice *qxl, QXLPHYSICAL pqxl,
- uint32_t *s, uint64_t *o)
+ uint32_t *s, uint64_t *o,
+ size_t size_requested)
{
uint64_t phys = le64_to_cpu(pqxl);
uint32_t slot = (phys >> (64 - 8)) & 0xff;
uint64_t offset = phys & 0xffffffffffff;
+ uint64_t size_available;
if (slot >= NUM_MEMSLOTS) {
qxl_set_guest_bug(qxl, "slot too large %d >= %d", slot,
@@ -1452,6 +1454,23 @@ static bool qxl_get_check_slot_offset(PCIQXLDevice *qxl,
QXLPHYSICAL pqxl,
slot, offset, qxl->guest_slots[slot].size);
return false;
}
+ size_available = memory_region_size(qxl->guest_slots[slot].mr);
+ if (qxl->guest_slots[slot].offset + offset >= size_available) {
+ qxl_set_guest_bug(qxl,
+ "slot %d offset %"PRIu64" > region size %"PRIu64"\n",
+ slot, qxl->guest_slots[slot].offset + offset,
+ size_available);
+ return false;
+ }
+ size_available -= qxl->guest_slots[slot].offset + offset;
+ if (size_requested > size_available) {
+ qxl_set_guest_bug(qxl,
+ "slot %d offset %"PRIu64" size %zu: "
+ "overrun by %"PRIu64" bytes\n",
+ slot, offset, size_requested,
+ size_requested - size_available);
+ return false;
+ }
*s = slot;
*o = offset;
@@ -1471,7 +1490,7 @@ void *qxl_phys2virt(PCIQXLDevice *qxl, QXLPHYSICAL pqxl,
int group_id,
offset = le64_to_cpu(pqxl) & 0xffffffffffff;
return (void *)(intptr_t)offset;
case MEMSLOT_GROUP_GUEST:
- if (!qxl_get_check_slot_offset(qxl, pqxl, &slot, &offset)) {
+ if (!qxl_get_check_slot_offset(qxl, pqxl, &slot, &offset, size)) {
return NULL;
}
ptr = memory_region_get_ram_ptr(qxl->guest_slots[slot].mr);
@@ -1937,9 +1956,9 @@ static void qxl_dirty_one_surface(PCIQXLDevice *qxl,
QXLPHYSICAL pqxl,
uint32_t slot;
bool rc;
- rc = qxl_get_check_slot_offset(qxl, pqxl, &slot, &offset);
- assert(rc == true);
size = (uint64_t)height * abs(stride);
+ rc = qxl_get_check_slot_offset(qxl, pqxl, &slot, &offset, size);
+ assert(rc == true);
trace_qxl_surfaces_dirty(qxl->id, offset, size);
qxl_set_dirty(qxl->guest_slots[slot].mr,
qxl->guest_slots[slot].offset + offset,
diff --git a/hw/display/qxl.h b/hw/display/qxl.h
index bf03138ab4..7894bd5134 100644
--- a/hw/display/qxl.h
+++ b/hw/display/qxl.h
@@ -157,7 +157,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(PCIQXLDevice, PCI_QXL)
*
* Returns a host pointer to a buffer placed at offset @phys within the
* active slot @group_id of the PCI VGA RAM memory region associated with
- * the @qxl device. If the slot is inactive, or the offset is out
+ * the @qxl device. If the slot is inactive, or the offset + size are out
* of the memory region, returns NULL.
*
* Use with care; by the time this function returns, the returned pointer is
--
2.38.1
- [RFC PATCH-for-7.2 v3 0/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt(), Philippe Mathieu-Daudé, 2022/11/28
- [PATCH-for-7.2 v3 1/5] hw/display/qxl: Have qxl_log_command Return early if no log_cmd handler, Philippe Mathieu-Daudé, 2022/11/28
- [PATCH-for-7.2 v3 2/5] hw/display/qxl: Document qxl_phys2virt(), Philippe Mathieu-Daudé, 2022/11/28
- [RFC PATCH-for-7.2 v3 3/5] hw/display/qxl: Pass requested buffer size to qxl_phys2virt(), Philippe Mathieu-Daudé, 2022/11/28
- [PATCH-for-8.0 v3 5/5] hw/display/qxl: Assert memory slot fits in preallocated MemoryRegion, Philippe Mathieu-Daudé, 2022/11/28
- [RFC PATCH-for-7.2 v3 4/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt (CVE-2022-4144),
Philippe Mathieu-Daudé <=
- Re: [RFC PATCH-for-7.2 v3 0/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt(), Stefan Hajnoczi, 2022/11/30