In the Linux kernel, the following vulnerability has been resolved:
drm/imagination: acquire vm_ctx->lock before mapping memory to GPU VM
The drm gpuvm code doesn't protect find operation against map operation, and the driver needs to ensure a map operation shouldn't happen when a find operation is in progress.
In some cases a find operation will be in progress when doing map/unmap operations, and the find operation will do a NULL pointer dereference.
An example of the stack trace of such NULL dereference is shown below:
Unable to handle kernel access to user memory without uaccess routines at
virtual address 0000000000000010[] drm_gpuva_find+0x28/0x6c [drm_gpuvm]
[] pvr_vm_unmap+0x34/0x68 [powervr]
[] pvr_ioctl_vm_unmap+0x2e/0x50 [powervr]
[] drm_ioctl_kernel+0x8e/0xdc
[] drm_ioctl+0x1be/0x3e0
[] __riscv_sys_ioctl+0xba/0xc4
[] do_trap_ecall_u+0x23e/0x3f4
[] handle_exception+0x168/0x174
As all occurences of drm_gpuva_find*() are already guarded by vm_ctx->lock, make pvr_vm_map() to acquire this lock to prevent disturbing any find operation. This fixes the NULL deference problem in drm_gpuva_find*().