On Mon, Jan 08, 2018 at 06:02:35PM +0100, Thomas Gleixner wrote: > On Mon, 8 Jan 2018, Willy Tarreau wrote: > > This allows to report the current state of the PTI protection and to > > enable or disable it for the current task. > > > > Signed-off-by: Willy Tarreau <[email protected]> > > --- > > arch/x86/include/uapi/asm/prctl.h | 3 +++ > > arch/x86/kernel/process_64.c | 24 ++++++++++++++++++++++++ > > 2 files changed, 27 insertions(+) > > > > diff --git a/arch/x86/include/uapi/asm/prctl.h > > b/arch/x86/include/uapi/asm/prctl.h > > index 5a6aac9..1f1b5bc 100644 > > --- a/arch/x86/include/uapi/asm/prctl.h > > +++ b/arch/x86/include/uapi/asm/prctl.h > > @@ -10,6 +10,9 @@ > > #define ARCH_GET_CPUID 0x1011 > > #define ARCH_SET_CPUID 0x1012 > > > > +#define ARCH_GET_NOPTI 0x1021 > > +#define ARCH_SET_NOPTI 0x1022 > > + > > #define ARCH_MAP_VDSO_X32 0x2001 > > #define ARCH_MAP_VDSO_32 0x2002 > > #define ARCH_MAP_VDSO_64 0x2003 > > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c > > index c754662..1686d3d 100644 > > --- a/arch/x86/kernel/process_64.c > > +++ b/arch/x86/kernel/process_64.c > > @@ -654,6 +654,30 @@ long do_arch_prctl_64(struct task_struct *task, int > > option, unsigned long arg2) > > ret = put_user(base, (unsigned long __user *)arg2); > > break; > > } > > + case ARCH_GET_NOPTI: { > > + unsigned long flag; > > + > > + printk(KERN_DEBUG "get1: task=%p ti=%p fl=%16lx\n", task, > > task_thread_info(task), task_thread_info(task)->flags); > > + flag = !!(task_thread_info(task)->flags & _TIF_NOPTI); > > + ret = put_user(flag, (unsigned long __user *)arg2); > > + break; > > Per task is really an odd choice. That should be per process I think, but > that of course needs synchronization of some form. Aside of that we need to > think about fork().
I also wondered how to do it and had no idea, but I wanted to start with something, also keeping in mind that I didn't want to risk losing in extra checks what we managed to previously save. I agree that it's not the best we can have. That said, other features seem to work like this, like TIF_NOTSC and TIF_NOCPUID, so it didn't look too odd at first glance. Willy
