On Thu, Sep 3, 2020 at 7:27 AM Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > > On 9/2/20 9:35 PM, Andy Lutomirski wrote: > >>>>>> + fpu__prepare_read(fpu); > >>>>>> + cetregs = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER); > >>>>>> + if (!cetregs) > >>>>>> + return -EFAULT; > >>>>> Can this branch ever be hit without a kernel bug? If yes, I think > >>>>> -EFAULT is probably a weird error code to choose here. If no, this > >>>>> should probably use WARN_ON(). Same thing in cetregs_set(). > >>>> When a thread is not CET-enabled, its CET state does not exist. I looked at EFAULT, and it means "Bad address". Maybe this can be ENODEV, which means "No such device"? > > Having read the code, I’m unconvinced. It looks like a get_xsave_addr() failure means “state not saved; task sees INIT state”. So *maybe* it’s reasonable -ENODEV this, but I’m not really convinced. I tend to think we should return the actual INIT state and that we should permit writes and handle them correctly. > > PTRACE is asking for access to the values in the *registers*, not for > the value in the kernel XSAVE buffer. We just happen to only have the > kernel XSAVE buffer around. > > If we want to really support PTRACE we have to allow the registers to be > get/set, regardless of what state they are in, INIT state or not. So, > yeah I agree with Andy. I think the core dump code gets here, too, so the values might be in registers as well. I hope that fpu__prepare_read() does the right thing in this case. --Andy
