On 10.10.18 19:35, Max Reitz wrote: > On 10.10.18 12:10, Gerd Hoffmann wrote: >> On Mon, Oct 08, 2018 at 08:50:13PM +0200, Max Reitz wrote: >>> There are some 2D resource formats that can be used through virtio-gpu, >> >> Ahem, not really. XRGB is the only one which works in practice, and >> virtio-gpu kms driver will stop advertising anything else soon (patches >> should land upstream with the next merge window). > > OK, if virtio-gpu didn't support anything else, that'd be a fix, too. > But it sounds like you're talking about the Linux driver, I'm not. > > This is not about Linux applications being able to abuse the Linux > driver to crash the VM, this is about malicious drivers (not necessarily > Linux drivers). > >>> Add these formats in the switch converting pixman to SDL format >>> constants so a guest cannot crash the VM by triggering the >>> g_assert_not_reached() with an unsupported format. >> >> Do you have a reproducer for that? > > I have attached two RISC-V kernels, one (kernel-rgbx) setting > VIRTIO_GPU_FORMAT_R8G8B8X8_UNORM, the other (kernel-bgra) setting > VIRTIO_GPU_FORMAT_B8G8R8A8_UNORM. Both crash qemu:
Of course I hadn't. > $ $QEMU/build/riscv64-softmmu/qemu-system-riscv64 -kernel kernel-rgbx \ > -serial stdio -M virt -device virtio-gpu-device > [platform-virt] Virt platform detected > [virtio-gpu] Found device @0x10008000 > [virtio-gpu] Scanout 0: 0x0:1024x768 > ** > ERROR:$QEMU/ui/sdl2-2d.c:114:sdl2_2d_switch: code should not be reached > [1] 7151 abort (core dumped) > > So this is not about a misbehaving Linux driver but about an own driver. > Of course, if you can insert kernel code, there's noone stopping you > from hitting that assertion with Linux, too. > >> There is sdl2_2d_check_format() which reports the supported formats. >> If we hit sdl2_2d_switch() with a format not whitelisted by >> sdl2_2d_check_format() we have a bug somewhere in qemu ... > > I suppose the other solution would be for virtio_gpu_set_scanout() to > check whether the resource's format can actually be used for that > display. Or in virtio_gpu_resource_create_2d(), I don't know whether > it's possible to use resources in other formats at all. > > Max >
kernel-rgbx.xz
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kernel-bgra.xz
Description: application/xz
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