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

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Date:   Mon, 8 Apr 2019 20:19:06 +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 Mon, 8 Apr 2019, Thomas Gleixner wrote:

> On Mon, 8 Apr 2019, Andy Lutomirski wrote:
> > On Sun, Apr 7, 2019 at 11:46 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> > >
> > > On Sun, 7 Apr 2019, Andy Lutomirski wrote:
> > > > On Sun, Apr 7, 2019 at 3:44 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> > > > > Actually we have: save_stack_trace()
> > > > >
> > > >
> > > > Like I did here:
> > > >
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=WIP.x86/stackguards
> > >
> > > Kinda, but what that code wants is to skip any entry before 'caller'. So we
> > > either add something like save_stack_trace_from() which is trivial on x86
> > > because unwind_start() already has an argument to hand in the start of
> > > stack or we filter out the entries up to 'caller' in that code.
> > >
> > >
> > Whoops!
> > 
> > I could add a save_stack_trace_from() or I could add a "caller"
> > argument to struct stack_trace.  Any preference as to which looks
> > better?  The latter seems a little nicer to me.

Bah, all that sucks. Because 'caller' is comes from __RET_IP__ and is not a
pointer to the stack. So this really needs to be a filter which prevents
storing an entry _before_ caller is seen on the stack.

ftrace and kasan do some post stacktrace filtering as well just different.

That's all bonkers. 

       tglx