linux-kernel - Re: [PATCH v14 06/14] arch/x86: enable task isolation functionality

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Date:	Wed, 10 Aug 2016 00:52:27 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Chris Metcalf <cmetcalf@...lanox.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <cl@...ux.com>,
	Gilad Ben Yossef <giladb@...lanox.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>, Will Deacon <will.deacon@....com>,
	Rik van Riel <riel@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v14 06/14] arch/x86: enable task isolation functionality

On Aug 9, 2016 11:30 PM, "Chris Metcalf" <cmetcalf@...lanox.com> wrote:
>
> In exit_to_usermode_loop(), call task_isolation_ready() for
> TIF_TASK_ISOLATION tasks when we are checking the thread-info flags,
> and after we've handled the other work, call task_isolation_enter()
> for such tasks.
>
> In syscall_trace_enter_phase1(), we add the necessary support for
> reporting syscalls for task-isolation processes.
>
> We add strict reporting for the kernel exception types that do
> not result in signals, namely non-signalling page faults and
> non-signalling MPX fixups.
>
> Tested-by: Christoph Lameter <cl@...ux.com>
> Signed-off-by: Chris Metcalf <cmetcalf@...lanox.com>
> ---
>  arch/x86/Kconfig                   |  1 +
>  arch/x86/entry/common.c            | 20 +++++++++++++++++++-
>  arch/x86/include/asm/thread_info.h |  2 ++
>  arch/x86/kernel/smp.c              |  2 ++
>  arch/x86/kernel/traps.c            |  3 +++
>  arch/x86/mm/fault.c                |  5 +++++
>  6 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5c6e7471b732..10b2c0567dad 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -89,6 +89,7 @@ config X86
>         select HAVE_ARCH_MMAP_RND_COMPAT_BITS   if MMU && COMPAT
>         select HAVE_ARCH_SECCOMP_FILTER
>         select HAVE_ARCH_SOFT_DIRTY             if X86_64
> +       select HAVE_ARCH_TASK_ISOLATION
>         select HAVE_ARCH_TRACEHOOK
>         select HAVE_ARCH_TRANSPARENT_HUGEPAGE
>         select HAVE_EBPF_JIT                    if X86_64
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index 1433f6b4607d..5c1b9fc89bf2 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -21,6 +21,7 @@
>  #include <linux/context_tracking.h>
>  #include <linux/user-return-notifier.h>
>  #include <linux/uprobes.h>
> +#include <linux/isolation.h>
>
>  #include <asm/desc.h>
>  #include <asm/traps.h>
> @@ -91,6 +92,15 @@ static long syscall_trace_enter(struct pt_regs *regs)
>         if (emulated)
>                 return -1L;
>
> +       /* In isolation mode, we may prevent the syscall from running. */
> +       if (work & _TIF_TASK_ISOLATION) {
> +               if (task_isolation_syscall(regs->orig_ax) == -1) {
> +                       regs->orig_ax = -1;
> +                       return 0;
> +               }
> +               work &= ~_TIF_TASK_ISOLATION;
> +       }
> +

What is this?  It's not mentioned in the changelog.  It seems
nonsensical to me.  If nothing else, you forgot to update regs->ax,
but I don't even know what you're trying to do.

>  #ifdef CONFIG_SECCOMP
>         /*
>          * Do seccomp after ptrace, to catch any tracer changes.
> @@ -136,7 +146,7 @@ static long syscall_trace_enter(struct pt_regs *regs)
>
>  #define EXIT_TO_USERMODE_LOOP_FLAGS                            \
>         (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |   \
> -        _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
> +        _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_TASK_ISOLATION)
>

Where are you updating the conditions to force use of the slow path?
(That's _TIF_ALLWORK_MASK.)

--Andy