Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 8 Apr 2019 00:44:24 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Andy Lutomirski <luto@kernel.org>
cc:     LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard
 pages
In-Reply-To: <CALCETrWF_YgQODJ=Rpm2MnhFxJXCfoo4H792hUQni0GS9on7og@mail.gmail.com>
Message-ID: <alpine.DEB.2.21.1904080043390.1840@nanos.tec.linutronix.de>
References: <20190405150658.237064784@linutronix.de> <20190405150930.967389183@linutronix.de> <CALCETrWF_YgQODJ=Rpm2MnhFxJXCfoo4H792hUQni0GS9on7og@mail.gmail.com>
User-Agent: Alpine 2.21 (DEB 202 2017-01-01)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sat, 6 Apr 2019, Andy Lutomirski wrote:
> On Fri, Apr 5, 2019 at 8:11 AM Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > From: Andy Lutomirski <luto@kernel.org>
> >
> > The IRQ stack lives in percpu space, so an IRQ handler that overflows it
> > will overwrite other data structures.
> >
> > Use vmap() to remap the IRQ stack so that it will have the usual guard
> > pages that vmap/vmalloc allocations have. With this the kernel will panic
> > immediately on an IRQ stack overflow.
> 
> The 0day bot noticed that this dies with DEBUG_PAGEALLOC on.  This is
> because the store_stackinfo() function is utter garbage and this patch
> correctly detects just how broken it is.  The attached patch "fixes"
> it.  (It also contains a reliability improvement that should probably
> get folded in, but is otherwise unrelated.)
> 
> A real fix would remove the generic kstack_end() function entirely
> along with __HAVE_ARCH_KSTACK_END and would optionally replace
> store_stackinfo() with something useful.  Josh, do we have a generic
> API to do a little stack walk like this?  Otherwise, I don't think it
> would be the end of the world to just remove the offending code.

Actually we have: save_stack_trace()