Messages in this thread | | | Date | Mon, 8 Jan 2018 18:17:59 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH RFC 2/4] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET_NOPTI to enable/disable PTI |
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* Thomas Gleixner <tglx@linutronix.de> 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 <w@1wt.eu> > > --- > > 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().
So per task (thread) is the most natural approach to low level asm flaggery.
Making it per thread also makes some sense conceptually: in a complex multi-threaded runtime implementation some threads might never execute 'untrusted' code, some might. No need to penalize the 'server' threads.
Not sure we want that complexity though, and while it _should_ work I think, mostly, there might be some unexpected implications.
Thanks,
Ingo
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