linux-kernel - Re: [PATCH] x86/dumpstack/64: Don't evaluate exception stacks before setup

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Message-ID: <20191023184336.GL12121@uranus.lan>
Date:   Wed, 23 Oct 2019 21:43:36 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
        Catalin Marinas <catalin.marinas@....com>, x86@...nel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] x86/dumpstack/64: Don't evaluate exception stacks before
 setup

On Wed, Oct 23, 2019 at 11:31:40AM -0700, Matthew Wilcox wrote:
> On Wed, Oct 23, 2019 at 08:05:49PM +0200, Thomas Gleixner wrote:
> > Prevent this by checking the validity of the cea_exception_stack base
> > address and bailing out if it is zero.
> 
> Could also initialise cea_exception_stack to -1?  That would lead to it
> being caught by ...
> 
> >  	end = begin + sizeof(struct cea_exception_stacks);
> >  	/* Bail if @stack is outside the exception stack area. */
> >  	if (stk < begin || stk >= end)
> 
> this existing check.

As to me this would be a hack and fragile :/ In turn the current explicit
test Thomas made is a way more readable.