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Date:   Wed, 5 Sep 2018 22:02:40 +0200 (CEST)
From:   Jiri Kosina <jikos@kernel.org>
To:     Andrea Arcangeli <aarcange@redhat.com>
cc:     Andi Kleen <ak@linux.intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        "Schaufler, Casey" <casey.schaufler@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        "Woodhouse, David" <dwmw@amazon.co.uk>,
        Oleg Nesterov <oleg@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>
Subject: Re: [PATCH v3 1/3] ptrace: Provide ___ptrace_may_access() that can
 be applied on arbitrary tasks
In-Reply-To: <20180905184018.GC11625@redhat.com>
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On Wed, 5 Sep 2018, Andrea Arcangeli wrote:

> [ 1838.621010] Kernel panic - not syncing: Watchdog detected hard LOCKUP on cpu 6
> [ 1838.629070] CPU: 6 PID: 0 Comm: swapper/6 Not tainted 3.10.0-327.62.4.el7.x86_64 #1
> [ 1838.637610] Hardware name: Dell Inc. PowerEdge R430/0CN7X8, BIOS 2.4.2 01/09/2017
> [ 1838.645954] Call Trace:
> [ 1838.648680]  <NMI>  [<ffffffff8163a05d>] dump_stack+0x19/0x1b
> [ 1838.655113]  [<ffffffff816338d0>] panic+0xd8/0x1e7
> [ 1838.660460]  [<ffffffff8111e960>] ? restart_watchdog_hrtimer+0x50/0x50
> [ 1838.667742]  [<ffffffff8111ea22>] watchdog_overflow_callback+0xc2/0xd0
> [ 1838.675024]  [<ffffffff81162211>] __perf_event_overflow+0xa1/0x250
> [ 1838.681920]  [<ffffffff81162ce4>] perf_event_overflow+0x14/0x20
> [ 1838.688526]  [<ffffffff810337c8>] intel_pmu_handle_irq+0x1e8/0x470
> [ 1838.695423]  [<ffffffff812f83cc>] ? ioremap_page_range+0x24c/0x330
> [ 1838.702320]  [<ffffffff811a9031>] ? unmap_kernel_range_noflush+0x11/0x20
> [ 1838.709797]  [<ffffffff813997f4>] ? ghes_copy_tofrom_phys+0x124/0x210
> [ 1838.716984]  [<ffffffff81399980>] ? ghes_read_estatus+0xa0/0x190
> [ 1838.723687]  [<ffffffff816444bb>] perf_event_nmi_handler+0x2b/0x50
> [ 1838.730582]  [<ffffffff81643c09>] nmi_handle.isra.0+0x69/0xb0
> [ 1838.736992]  [<ffffffff81643db9>] do_nmi+0x169/0x340
> [ 1838.742532]  [<ffffffff81642ff9>] end_repeat_nmi+0x1e/0x7e
> [ 1838.748653]  [<ffffffff81641bbd>] ? _raw_spin_lock_irqsave+0x3d/0x60
> [ 1838.755742]  [<ffffffff81641bbd>] ? _raw_spin_lock_irqsave+0x3d/0x60
> [ 1838.762831]  [<ffffffff81641bbd>] ? _raw_spin_lock_irqsave+0x3d/0x60
> [ 1838.769917]  <<EOE>>  [<ffffffff816391e5>] avc_compute_av+0x126/0x1b5
> [ 1838.777125]  [<ffffffff810b842e>] ? walk_tg_tree_from+0xbe/0x110
> [ 1838.783828]  [<ffffffff8128b9c4>] avc_has_perm_noaudit+0xc4/0x110
> [ 1838.790628]  [<ffffffff8128f1fb>] cred_has_capability+0x6b/0x120
> [ 1838.797331]  [<ffffffff810db71c>] ? ktime_get+0x4c/0xd0
> [ 1838.803160]  [<ffffffff810e167b>] ? clockevents_program_event+0x6b/0xf0
> [ 1838.810532]  [<ffffffff8128f2de>] selinux_capable+0x2e/0x40
> [ 1838.816748]  [<ffffffff81288f65>] security_capable_noaudit+0x15/0x20
> [ 1838.823829]  [<ffffffff8108b975>] has_ns_capability_noaudit+0x15/0x20
> [ 1838.831014]  [<ffffffff8108bc55>] ptrace_has_cap+0x35/0x40
> [ 1838.837126]  [<ffffffff8108c717>] ___ptrace_may_access+0xa7/0x1e0
> [ 1838.843925]  [<ffffffff8163f0ae>] __schedule+0x26e/0xa00
> [ 1838.849855]  [<ffffffff81640949>] schedule_preempt_disabled+0x29/0x70
> [ 1838.857041]  [<ffffffff810d9324>] cpu_startup_entry+0x184/0x290
> [ 1838.863637]  [<ffffffff8104891a>] start_secondary+0x1da/0x250

So yeah, current Linus' tree needs the same treatment -- we have to avoid 
calling out to ptrace_has_cap() in PTRACE_MODE_NOACCESS_CHK cases.

I have updated the patch for v4. Thanks again,

-- 
Jiri Kosina
SUSE Labs