In the function sbusfb_ioctl_helper() in drivers/video/fbdev/sbuslib.c in the Linux kernel through 4.15, an integer signedness error allows arbitrary information leakage for the FBIOPUTCMAP_SPARC and FBIOGETCMAP_SPARC commands.
https://marc.info/?l=linux-fbdev&m=151734425901499&w=2
https://github.com/torvalds/linux/commit/250c6c49e3b68756b14983c076183568636e2bde