Re: [PATCH RFC 2/4] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET_NOPTI to enable/disable PTI

[Thomas Gleixner]

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 <w@xxxxxx>
> ---
>  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().

Thanks,

	tglx