linux-kernel - Re: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard pages

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Message-ID: <alpine.DEB.2.21.1904080043390.1840@nanos.tec.linutronix.de>
Date:   Mon, 8 Apr 2019 00:44:24 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard
 pages

On Sat, 6 Apr 2019, Andy Lutomirski wrote:
> On Fri, Apr 5, 2019 at 8:11 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > From: Andy Lutomirski <luto@...nel.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()