[PATCH] drm: drm_bufs: Error out if 'dev->agp' is a null pointer

[Zheyu Ma]

On Thu, Mar 17, 2022 at 6:49 PM Daniel Vetter <daniel at ffwll.ch> wrote:
>
> On Fri, Mar 11, 2022 at 07:23:02AM +0000, Zheyu Ma wrote:
> > The user program can control the 'drm_buf_desc::flags' via ioctl system
> > call and enter the function drm_legacy_addbufs_agp(). If the driver
> > doesn't initialize the agp resources, the driver will cause a null
> > pointer dereference.
> >
> > The following log reveals it:
> >     general protection fault, probably for non-canonical address
> >     0xdffffc000000000f: 0000 [#1] PREEMPT SMP KASAN PTI
> >     KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f]
> >     Call Trace:
> >      <TASK>
> >      drm_ioctl_kernel+0x342/0x450 drivers/gpu/drm/drm_ioctl.c:785
> >      drm_ioctl+0x592/0x940 drivers/gpu/drm/drm_ioctl.c:885
> >      vfs_ioctl fs/ioctl.c:51 [inline]
> >      __do_sys_ioctl fs/ioctl.c:874 [inline]
> >      __se_sys_ioctl+0xaa/0xf0 fs/ioctl.c:860
> >      do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >      do_syscall_64+0x43/0x90 arch/x86/entry/common.c:80
> >      entry_SYSCALL_64_after_hwframe+0x44/0xae
> >
> > Fix this bug by adding a check.
> >
> > Signed-off-by: Zheyu Ma <zheyuma97 at gmail.com>
>
> You can only hit this if you enabled a DRIVER_LEGACY drm driver, which
> opens you up to tons of other CVEs and issues. What's your .config?

Yes, I enable the DRM_LEGACY option in the config.
I think you mean this is not a normal configuration file? Do you have
a recommended configuration option for when I want to test the GPU
driver?

Actually, I use the following configs related to GPU:

CONFIG_AGP=y
CONFIG_AGP_AMD64=y
CONFIG_AGP_INTEL=y
CONFIG_AGP_SIS=y
CONFIG_AGP_VIA=y
CONFIG_INTEL_GTT=y
CONFIG_VGA_ARB=y
CONFIG_VGA_ARB_MAX_GPUS=16
CONFIG_DRM=y
CONFIG_DRM_MIPI_DSI=y
CONFIG_DRM_KMS_HELPER=y
CONFIG_DRM_DEBUG_MODESET_LOCK=y
CONFIG_DRM_FBDEV_EMULATION=y
CONFIG_DRM_FBDEV_OVERALLOC=100
CONFIG_DRM_TTM=y
CONFIG_DRM_VRAM_HELPER=y
CONFIG_DRM_TTM_HELPER=y
CONFIG_DRM_GEM_SHMEM_HELPER=y
CONFIG_DRM_SCHED=y
CONFIG_DRM_RADEON=y
CONFIG_DRM_AMDGPU=y
CONFIG_DRM_AMD_DC=y
CONFIG_DRM_AMD_DC_DCN=y
CONFIG_DRM_I915=y
CONFIG_DRM_I915_FORCE_PROBE=""
CONFIG_DRM_I915_CAPTURE_ERROR=y
CONFIG_DRM_I915_COMPRESS_ERROR=y
CONFIG_DRM_I915_USERPTR=y
CONFIG_DRM_I915_REQUEST_TIMEOUT=20000
CONFIG_DRM_I915_FENCE_TIMEOUT=10000
CONFIG_DRM_I915_USERFAULT_AUTOSUSPEND=250
CONFIG_DRM_I915_HEARTBEAT_INTERVAL=2500
CONFIG_DRM_I915_PREEMPT_TIMEOUT=640
CONFIG_DRM_I915_MAX_REQUEST_BUSYWAIT=8000
CONFIG_DRM_I915_STOP_TIMEOUT=100
CONFIG_DRM_I915_TIMESLICE_DURATION=1
CONFIG_DRM_VMWGFX=y
CONFIG_DRM_GMA500=y
CONFIG_DRM_UDL=y
CONFIG_DRM_AST=y
CONFIG_DRM_MGAG200=y
CONFIG_DRM_QXL=y
CONFIG_DRM_VIRTIO_GPU=y
CONFIG_DRM_PANEL=y
CONFIG_DRM_BRIDGE=y
CONFIG_DRM_PANEL_BRIDGE=y
CONFIG_DRM_BOCHS=y
CONFIG_DRM_CIRRUS_QEMU=y
CONFIG_DRM_GM12U320=y
CONFIG_DRM_VBOXVIDEO=y
CONFIG_DRM_GUD=y
CONFIG_DRM_HYPERV=y
CONFIG_DRM_LEGACY=y
CONFIG_DRM_TDFX=y
CONFIG_DRM_R128=y
CONFIG_DRM_MGA=y
CONFIG_DRM_SIS=y
CONFIG_DRM_VIA=y
CONFIG_DRM_SAVAGE=y
CONFIG_DRM_PANEL_ORIENTATION_QUIRKS=y

Thanks,
Zheyu Ma