fpregs_state_valid in arch/x86/include/asm/fpu/internal.h in the Linux kernel before 5.4.2, when GCC 9 is used, allows context-dependent attackers to cause a denial of service (memory corruption) or possibly have unspecified other impact because of incorrect fpu_fpregs_owner_ctx caching, as demonstrated by mishandling of signal-based non-cooperative preemption in Go 1.14 prereleases on amd64, aka CID-59c4bd853abc.