linux-kernel - Re: [PATCH v6 0/3] Harden spectrev2 userspace-userspace protection

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Date:   Wed, 19 Sep 2018 17:48:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Schaufler, Casey" <casey.schaufler@...el.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v6 0/3] Harden spectrev2 userspace-userspace protection

On Mon, Sep 17, 2018 at 04:09:33PM +0000, Schaufler, Casey wrote:

> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 5c5e7cb597cd..202a4d9c2af7 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -330,9 +330,7 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
>                !ptrace_has_cap(mm->user_ns, mode))))
>             return -EPERM;
> 
> -       if (!(mode & PTRACE_MODE_NOACCESS_CHK))
> -               return security_ptrace_access_check(task, mode);
> -       return 0;
> +       return security_ptrace_access_check(task, mode);
>  }
> 
>  bool ptrace_may_access(struct task_struct *task, unsigned int mode)
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 161a4f29f860..30d21142e9fe 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2215,7 +2215,12 @@ static int selinux_ptrace_access_check(struct task_struct *child,
>  {
>         u32 sid = current_sid();
>         u32 csid = task_sid(child);
> +       struct av_decision avd;
> 
> +       if (mode == PTRACE_MODE_IBPB)
> +               return avc_has_perm_noaudit(&selinux_state, sid, csid,
> +                                           SECCLASS_PROCESS, PROCESS__PTRACE,
> +                                           0, &avd);
>         if (mode & PTRACE_MODE_READ)
>                 return avc_has_perm(&selinux_state,
>                                     sid, csid, SECCLASS_FILE, FILE__READ, NULL);
> 

As far as I can tell, this still has:

	avc_has_perm_noaudit()
	  security_compute_av()
	    read_lock(&state->ss->policy_rwlock);
	  avc_insert()
	    spin_lock_irqsave();
	  avc_denied()
	    avc_update_node()
	      spin_lock_irqsave();

under the scheduler's raw_spinlock_t, which are invalid lock nestings.