On 2/1/21 2:43 PM, Yu, Yu-cheng wrote: > On 1/29/2021 2:53 PM, Dave Hansen wrote: >> On 1/29/21 2:35 PM, Yu, Yu-cheng wrote: >>>> Andy Cooper just mentioned on IRC about this nugget in the spec: >>>> >>>> XRSTORS on CET state will do reserved bit and canonicality >>>> checks on the state in similar manner as done by the WRMSR to >>>> these state elements. >>>> >>>> We're using copy_kernel_to_xregs_err(), so the #GP *should* be OK. >>>> Could we prove this out in practice, please? >>>>> >>> Do we want to verify that setting reserved bits in CET XSAVES states >>> triggers GP? Then, yes, I just verified it again. Thanks for >>> reminding. Do we have any particular case relating to this? >> >> I want to confirm that it triggers #GP and kills userspace without the >> kernel WARN'ing or otherwise being visibly unhappy. > > For sigreturn, shadow stack pointer is checked against its restore token > and must be smaller than TASK_SIZE_MAX. Sigreturn cannot set any > MSR_IA32_U_CET reserved bits. That would be nice to at least allude to in the changelog or comments. >> What about the return-to-userspace path after a ptracer writes content >> to the CET fields? I don't see the same tolerance for errors in >> __fpregs_load_activate(), for instance. >> > > Good thought. I have not sent out my revised PTRACE patch, but values > from user will be checked for valid address and reserved bits. Wait a sec... What about *THIS* series? Will *THIS* series give us oopses when userspace blasts a new XSAVE buffer in with NT_X86_XSTATE?
