[Qemu-devel] [PATCH v2 2/4] spice: fix invalid memory access to vga.vram

["Radim Krčmář" <rkrcmar@redhat.com>]

vga_common_init() doesn't allow more than 256 MiB vram size and silently
shrinks any larger value.  qxl_dirty_surfaces() used the unshrinked size
via qxl->shadow_rom.surface0_area_size when accessing the memory, which
resulted in segfault.

Add a workaround for this case and an assert if it happens again.

We have to bump the vga memory limit too, because 256 MiB wouldn't have
allowed 8k (it requires more than 128 MiB).
1024 MiB doesn't work, but 512 MiB seems fine.

Proposed-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v2: changed numbers in Gerd's solution, added an assert and a comment
     (was [v1 2/2])
 
 hw/display/qxl.c | 8 ++++++++
 hw/display/vga.c | 4 ++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/hw/display/qxl.c b/hw/display/qxl.c
index 6e9079783e27..92f2d5025d70 100644
--- a/hw/display/qxl.c
+++ b/hw/display/qxl.c
@@ -370,6 +370,8 @@ static void init_qxl_rom(PCIQXLDevice *d)
     num_pages         -= surface0_area_size;
     num_pages          = num_pages / QXL_PAGE_SIZE;
 
+    assert(ram_header_size + surface0_area_size <= d->vga.vram_size);
+
     rom->draw_area_offset   = cpu_to_le32(0);
     rom->surface0_area_size = cpu_to_le32(surface0_area_size);
     rom->pages_offset       = cpu_to_le32(surface0_area_size);
@@ -1883,6 +1885,12 @@ static void qxl_init_ramsize(PCIQXLDevice *qxl)
     if (qxl->vgamem_size_mb < 8) {
         qxl->vgamem_size_mb = 8;
     }
+    /* XXX: we round vgamem_size_mb up to a nearest power of two and it must be
+     * less than vga_common_init()'s maximum on qxl->vga.vram_size (512 now).
+     */
+    if (qxl->vgamem_size_mb > 256) {
+        qxl->vgamem_size_mb = 256;
+    }
     qxl->vgamem_size = qxl->vgamem_size_mb * 1024 * 1024;
 
     /* vga ram (bar 0, total) */
diff --git a/hw/display/vga.c b/hw/display/vga.c
index 9c62fbf48823..13f34f950d5a 100644
--- a/hw/display/vga.c
+++ b/hw/display/vga.c
@@ -2122,10 +2122,10 @@ void vga_common_init(VGACommonState *s, Object *obj, bool global_vmstate)
         expand4to8[i] = v;
     }
 
-    /* valid range: 1 MB -> 256 MB */
+    /* valid range: 1 MB -> 512 MB */
     s->vram_size = 1024 * 1024;
     while (s->vram_size < (s->vram_size_mb << 20) &&
-           s->vram_size < (256 << 20)) {
+           s->vram_size < (512 << 20)) {
         s->vram_size <<= 1;
     }
     s->vram_size_mb = s->vram_size >> 20;
-- 
2.3.0