linux-kernel - Re: [patch V2 19/29] x86/exceptions: Split debug IST stack

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Message-ID: <alpine.DEB.2.21.1904052300500.1802@nanos.tec.linutronix.de>
Date:   Fri, 5 Apr 2019 23:01:16 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [patch V2 19/29] x86/exceptions: Split debug IST stack

On Fri, 5 Apr 2019, Sean Christopherson wrote:
> On Fri, Apr 05, 2019 at 05:07:17PM +0200, Thomas Gleixner wrote:
> > +	/*
> > +	 * Note, this covers the guard page between DB and DB1 as well to
> > +	 * avoid two checks. But by all means @addr can never point into
> > +	 * the guard page.
> > +	 */
> > +	return addr > bot && addr < top;
> 
> Isn't this an off by one error?  I.e. "return addr >= bot && addr < top".
> %rsp == bot is technically still in the DB1 stack even though the next
> PUSH/CALL will explode on the guard page.

Right you are.