[RFC PATCH-for-7.2 v3 0/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt()

[RFC PATCH-for-7.2 v3 0/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt()

[Philippe Mathieu-Daudé]

Since v2:
- Do not abort checking guest-provided addresses (Stefan)
- Handle chunked QEMUCursor (Gerd)

Since v1:
- Moved overrun check in qxl_get_check_slot_offset (Marc-André)

memory_region_get_ram_ptr() returns a host pointer for a
MemoryRegion. Sometimes we do offset calculation using this
pointer without checking the underlying MemoryRegion size.

Wenxu Yin reported a buffer overrun in QXL. This series
aims to fix it. I haven't audited the other _get_ram_ptr()
uses (yet). Eventually we could rename it _get_ram_ptr_unsafe
and add a safer helper which checks for overrun.

Worth considering for 7.2?

Regards,

Phil.

Philippe Mathieu-Daudé (5):
  hw/display/qxl: Have qxl_log_command Return early if no log_cmd
    handler
  hw/display/qxl: Document qxl_phys2virt()
  hw/display/qxl: Pass requested buffer size to qxl_phys2virt()
  hw/display/qxl: Avoid buffer overrun in qxl_phys2virt (CVE-2022-4144)
  hw/display/qxl: Assert memory slot fits in preallocated MemoryRegion

 hw/display/qxl-logger.c | 22 ++++++++++++++++++---
 hw/display/qxl-render.c | 20 ++++++++++++++++----
 hw/display/qxl.c        | 42 ++++++++++++++++++++++++++++++++---------
 hw/display/qxl.h        | 23 +++++++++++++++++++++-
 4 files changed, 90 insertions(+), 17 deletions(-)

-- 
2.38.1

[PATCH-for-7.2 v3 1/5] hw/display/qxl: Have qxl_log_command Return early if no log_cmd handler

[Philippe Mathieu-Daudé]

Only 3 command types are logged: no need to call qxl_phys2virt()
for the other types. Using different cases will help to pass
different structure sizes to qxl_phys2virt() in a pair of commits.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/display/qxl-logger.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/hw/display/qxl-logger.c b/hw/display/qxl-logger.c
index 68bfa47568..1bcf803db6 100644
--- a/hw/display/qxl-logger.c
+++ b/hw/display/qxl-logger.c
@@ -247,6 +247,16 @@ int qxl_log_command(PCIQXLDevice *qxl, const char *ring, QXLCommandExt *ext)
             qxl_name(qxl_type, ext->cmd.type),
             compat ? "(compat)" : "");
 
+    switch (ext->cmd.type) {
+    case QXL_CMD_DRAW:
+        break;
+    case QXL_CMD_SURFACE:
+        break;
+    case QXL_CMD_CURSOR:
+        break;
+    default:
+        goto out;
+    }
     data = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
     if (!data) {
         return 1;
@@ -269,6 +279,7 @@ int qxl_log_command(PCIQXLDevice *qxl, const char *ring, QXLCommandExt *ext)
         qxl_log_cmd_cursor(qxl, data, ext->group_id);
         break;
     }
+out:
     fprintf(stderr, "\n");
     return 0;
 }
-- 
2.38.1

[PATCH-for-7.2 v3 2/5] hw/display/qxl: Document qxl_phys2virt()

[Philippe Mathieu-Daudé]

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/display/qxl.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/hw/display/qxl.h b/hw/display/qxl.h
index e74de9579d..78b3a6c9ba 100644
--- a/hw/display/qxl.h
+++ b/hw/display/qxl.h
@@ -147,6 +147,25 @@ OBJECT_DECLARE_SIMPLE_TYPE(PCIQXLDevice, PCI_QXL)
 #define QXL_DEFAULT_REVISION (QXL_REVISION_STABLE_V12 + 1)
 
 /* qxl.c */
+/**
+ * qxl_phys2virt: Get a pointer within a PCI VRAM memory region.
+ *
+ * @qxl: QXL device
+ * @phys: physical offset of buffer within the VRAM
+ * @group_id: memory slot group
+ *
+ * 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
+ * of the memory region, returns NULL.
+ *
+ * Use with care; by the time this function returns, the returned pointer is
+ * not protected by RCU anymore.  If the caller is not within an RCU critical
+ * section and does not hold the iothread lock, it must have other means of
+ * protecting the pointer, such as a reference to the region that includes
+ * the incoming ram_addr_t.
+ *
+ */
 void *qxl_phys2virt(PCIQXLDevice *qxl, QXLPHYSICAL phys, int group_id);
 void qxl_set_guest_bug(PCIQXLDevice *qxl, const char *msg, ...)
     G_GNUC_PRINTF(2, 3);
-- 
2.38.1

[RFC PATCH-for-7.2 v3 3/5] hw/display/qxl: Pass requested buffer size to qxl_phys2virt()

[Philippe Mathieu-Daudé]

Currently qxl_phys2virt() doesn't check for buffer overrun.
In order to do so in the next commit, pass the buffer size
as argument.

For QXLCursor in qxl_render_cursor() -> qxl_cursor() we
verify the size of the chunked data ahead, checking we can
access 'sizeof(QXLCursor) + chunk->data_size' bytes.
Since in the SPICE_CURSOR_TYPE_MONO case the cursor is
assumed to fit in one chunk, no change are required.
In SPICE_CURSOR_TYPE_ALPHA the ahead read is handled in
qxl_unpack_chunks().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
Except the QXLCursor changes, v2 had:
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

 hw/display/qxl-logger.c | 11 ++++++++---
 hw/display/qxl-render.c | 20 ++++++++++++++++----
 hw/display/qxl.c        | 14 +++++++++-----
 hw/display/qxl.h        |  4 +++-
 4 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/hw/display/qxl-logger.c b/hw/display/qxl-logger.c
index 1bcf803db6..35c38f6252 100644
--- a/hw/display/qxl-logger.c
+++ b/hw/display/qxl-logger.c
@@ -106,7 +106,7 @@ static int qxl_log_image(PCIQXLDevice *qxl, QXLPHYSICAL addr, int group_id)
     QXLImage *image;
     QXLImageDescriptor *desc;
 
-    image = qxl_phys2virt(qxl, addr, group_id);
+    image = qxl_phys2virt(qxl, addr, group_id, sizeof(QXLImage));
     if (!image) {
         return 1;
     }
@@ -214,7 +214,8 @@ int qxl_log_cmd_cursor(PCIQXLDevice *qxl, QXLCursorCmd *cmd, int group_id)
                 cmd->u.set.position.y,
                 cmd->u.set.visible ? "yes" : "no",
                 cmd->u.set.shape);
-        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, group_id);
+        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, group_id,
+                               sizeof(QXLCursor));
         if (!cursor) {
             return 1;
         }
@@ -236,6 +237,7 @@ int qxl_log_command(PCIQXLDevice *qxl, const char *ring, QXLCommandExt *ext)
 {
     bool compat = ext->flags & QXL_COMMAND_FLAG_COMPAT;
     void *data;
+    size_t datasz;
     int ret;
 
     if (!qxl->cmdlog) {
@@ -249,15 +251,18 @@ int qxl_log_command(PCIQXLDevice *qxl, const char *ring, QXLCommandExt *ext)
 
     switch (ext->cmd.type) {
     case QXL_CMD_DRAW:
+        datasz = compat ? sizeof(QXLCompatDrawable) : sizeof(QXLDrawable);
         break;
     case QXL_CMD_SURFACE:
+        datasz = sizeof(QXLSurfaceCmd);
         break;
     case QXL_CMD_CURSOR:
+        datasz = sizeof(QXLCursorCmd);
         break;
     default:
         goto out;
     }
-    data = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
+    data = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id, datasz);
     if (!data) {
         return 1;
     }
diff --git a/hw/display/qxl-render.c b/hw/display/qxl-render.c
index ca217004bf..fcfd40c3ac 100644
--- a/hw/display/qxl-render.c
+++ b/hw/display/qxl-render.c
@@ -107,7 +107,9 @@ static void qxl_render_update_area_unlocked(PCIQXLDevice *qxl)
         qxl->guest_primary.resized = 0;
         qxl->guest_primary.data = qxl_phys2virt(qxl,
                                                 qxl->guest_primary.surface.mem,
-                                                MEMSLOT_GROUP_GUEST);
+                                                MEMSLOT_GROUP_GUEST,
+                                                qxl->guest_primary.abs_stride
+                                                * height);
         if (!qxl->guest_primary.data) {
             goto end;
         }
@@ -228,7 +230,8 @@ static void qxl_unpack_chunks(void *dest, size_t size, PCIQXLDevice *qxl,
         if (offset == size) {
             return;
         }
-        chunk = qxl_phys2virt(qxl, chunk->next_chunk, group_id);
+        chunk = qxl_phys2virt(qxl, chunk->next_chunk, group_id,
+                              sizeof(QXLDataChunk) + chunk->data_size);
         if (!chunk) {
             return;
         }
@@ -295,7 +298,8 @@ fail:
 /* called from spice server thread context only */
 int qxl_render_cursor(PCIQXLDevice *qxl, QXLCommandExt *ext)
 {
-    QXLCursorCmd *cmd = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
+    QXLCursorCmd *cmd = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id,
+                                      sizeof(QXLCursorCmd));
     QXLCursor *cursor;
     QEMUCursor *c;
 
@@ -314,7 +318,15 @@ int qxl_render_cursor(PCIQXLDevice *qxl, QXLCommandExt *ext)
     }
     switch (cmd->type) {
     case QXL_CURSOR_SET:
-        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, ext->group_id);
+        /* First read the QXLCursor to get QXLDataChunk::data_size ... */
+        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, ext->group_id,
+                               sizeof(QXLCursor));
+        if (!cursor) {
+            return 1;
+        }
+        /* Then read including the chunked data following QXLCursor. */
+        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, ext->group_id,
+                               sizeof(QXLCursor) + cursor->chunk.data_size);
         if (!cursor) {
             return 1;
         }
diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 5b10f697f1..231d733250 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -274,7 +274,8 @@ static void qxl_spice_monitors_config_async(PCIQXLDevice *qxl, int replay)
                                           QXL_IO_MONITORS_CONFIG_ASYNC));
     }
 
-    cfg = qxl_phys2virt(qxl, qxl->guest_monitors_config, MEMSLOT_GROUP_GUEST);
+    cfg = qxl_phys2virt(qxl, qxl->guest_monitors_config, MEMSLOT_GROUP_GUEST,
+                        sizeof(QXLMonitorsConfig));
     if (cfg != NULL && cfg->count == 1) {
         qxl->guest_primary.resized = 1;
         qxl->guest_head0_width  = cfg->heads[0].width;
@@ -459,7 +460,8 @@ static int qxl_track_command(PCIQXLDevice *qxl, struct QXLCommandExt *ext)
     switch (le32_to_cpu(ext->cmd.type)) {
     case QXL_CMD_SURFACE:
     {
-        QXLSurfaceCmd *cmd = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
+        QXLSurfaceCmd *cmd = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id,
+                                           sizeof(QXLSurfaceCmd));
 
         if (!cmd) {
             return 1;
@@ -494,7 +496,8 @@ static int qxl_track_command(PCIQXLDevice *qxl, struct QXLCommandExt *ext)
     }
     case QXL_CMD_CURSOR:
     {
-        QXLCursorCmd *cmd = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id);
+        QXLCursorCmd *cmd = qxl_phys2virt(qxl, ext->cmd.data, ext->group_id,
+                                          sizeof(QXLCursorCmd));
 
         if (!cmd) {
             return 1;
@@ -1456,7 +1459,8 @@ static bool qxl_get_check_slot_offset(PCIQXLDevice *qxl, QXLPHYSICAL pqxl,
 }
 
 /* can be also called from spice server thread context */
-void *qxl_phys2virt(PCIQXLDevice *qxl, QXLPHYSICAL pqxl, int group_id)
+void *qxl_phys2virt(PCIQXLDevice *qxl, QXLPHYSICAL pqxl, int group_id,
+                    size_t size)
 {
     uint64_t offset;
     uint32_t slot;
@@ -1964,7 +1968,7 @@ static void qxl_dirty_surfaces(PCIQXLDevice *qxl)
         }
 
         cmd = qxl_phys2virt(qxl, qxl->guest_surfaces.cmds[i],
-                            MEMSLOT_GROUP_GUEST);
+                            MEMSLOT_GROUP_GUEST, sizeof(QXLSurfaceCmd));
         assert(cmd);
         assert(cmd->type == QXL_SURFACE_CMD_CREATE);
         qxl_dirty_one_surface(qxl, cmd->u.surface_create.data,
diff --git a/hw/display/qxl.h b/hw/display/qxl.h
index 78b3a6c9ba..bf03138ab4 100644
--- a/hw/display/qxl.h
+++ b/hw/display/qxl.h
@@ -153,6 +153,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(PCIQXLDevice, PCI_QXL)
  * @qxl: QXL device
  * @phys: physical offset of buffer within the VRAM
  * @group_id: memory slot group
+ * @size: size of the buffer
  *
  * 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
@@ -166,7 +167,8 @@ OBJECT_DECLARE_SIMPLE_TYPE(PCIQXLDevice, PCI_QXL)
  * the incoming ram_addr_t.
  *
  */
-void *qxl_phys2virt(PCIQXLDevice *qxl, QXLPHYSICAL phys, int group_id);
+void *qxl_phys2virt(PCIQXLDevice *qxl, QXLPHYSICAL phys, int group_id,
+                    size_t size);
 void qxl_set_guest_bug(PCIQXLDevice *qxl, const char *msg, ...)
     G_GNUC_PRINTF(2, 3);
 
-- 
2.38.1

[RFC PATCH-for-7.2 v3 4/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt (CVE-2022-4144)

[Philippe Mathieu-Daudé]

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

[PATCH-for-8.0 v3 5/5] hw/display/qxl: Assert memory slot fits in preallocated MemoryRegion

[Philippe Mathieu-Daudé]

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/display/qxl.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 0b21626aad..6772849dec 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -1384,6 +1384,7 @@ static int qxl_add_memslot(PCIQXLDevice *d, uint32_t slot_id, uint64_t delta,
         qxl_set_guest_bug(d, "%s: pci_region = %d", __func__, pci_region);
         return 1;
     }
+    assert(guest_end - pci_start <= memory_region_size(mr));
 
     virt_start = (intptr_t)memory_region_get_ram_ptr(mr);
     memslot.slot_id = slot_id;
-- 
2.38.1

Re: [RFC PATCH-for-7.2 v3 3/5] hw/display/qxl: Pass requested buffer size to qxl_phys2virt()

[Gerd Hoffmann]

> @@ -228,7 +230,8 @@ static void qxl_unpack_chunks(void *dest, size_t size, PCIQXLDevice *qxl,
>          if (offset == size) {
>              return;
>          }
> -        chunk = qxl_phys2virt(qxl, chunk->next_chunk, group_id);
> +        chunk = qxl_phys2virt(qxl, chunk->next_chunk, group_id,
> +                              sizeof(QXLDataChunk) + chunk->data_size);
>          if (!chunk) {
>              return;
>          }

Not checking the first chunk?

> @@ -314,7 +318,15 @@ int qxl_render_cursor(PCIQXLDevice *qxl, QXLCommandExt *ext)
>      }
>      switch (cmd->type) {
>      case QXL_CURSOR_SET:
> -        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, ext->group_id);
> +        /* First read the QXLCursor to get QXLDataChunk::data_size ... */
> +        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, ext->group_id,
> +                               sizeof(QXLCursor));
> +        if (!cursor) {
> +            return 1;
> +        }
> +        /* Then read including the chunked data following QXLCursor. */
> +        cursor = qxl_phys2virt(qxl, cmd->u.set.shape, ext->group_id,
> +                               sizeof(QXLCursor) + cursor->chunk.data_size);
>          if (!cursor) {
>              return 1;
>          }

Ah, you do it here.  Good.

Series:
Acked-by: Gerd Hoffmann <kraxel@redhat.com>

take care,
  Gerd

Re: [RFC PATCH-for-7.2 v3 0/5] hw/display/qxl: Avoid buffer overrun in qxl_phys2virt()

[Stefan Hajnoczi]

On Mon, 28 Nov 2022 at 15:30, Philippe Mathieu-Daudé <philmd@linaro.org> wrote:
>
> Since v2:
> - Do not abort checking guest-provided addresses (Stefan)
> - Handle chunked QEMUCursor (Gerd)
>
> Since v1:
> - Moved overrun check in qxl_get_check_slot_offset (Marc-André)
>
> memory_region_get_ram_ptr() returns a host pointer for a
> MemoryRegion. Sometimes we do offset calculation using this
> pointer without checking the underlying MemoryRegion size.
>
> Wenxu Yin reported a buffer overrun in QXL. This series
> aims to fix it. I haven't audited the other _get_ram_ptr()
> uses (yet). Eventually we could rename it _get_ram_ptr_unsafe
> and add a safer helper which checks for overrun.
>
> Worth considering for 7.2?

Merged, thanks!

Stefan