On Tue, Sep 19, 2017 at 05:44:34PM -0700, Eric Biggers wrote: > +/* > + * We should never get here because the fpregs_state stored in 'struct fpu' > + * should always be readable and contain a valid FPU state. However, past > bugs > + * have allowed userspace to set reserved bits in the XSAVE area using > + * PTRACE_SETREGSET or sys_rt_sigreturn(). These caused XRSTOR to fail when > + * switching to the task, leaking the FPU registers of the task previously > + * executing on the CPU. Mitigate this class of vulnerability by restoring > from > + * the initial state (essentially, zeroing out all the FPU registers) if we > + * can't restore from the task's FPU state. > + */ > +void __handle_bad_fpstate(union fpregs_state *fpstate, u64 mask) > +{ > + WARN_ONCE(1, "Bad FPU state detected, reinitializing FPU registers"); > + ____copy_kernel_to_fpregs(&init_fpstate, mask); > +}
Sorry, a small oversight here --- this needs to be exported to modules, since kvm can be built as a module, and kvm uses __copy_kernel_to_fpregs(). Eric