linux-kernel - Re: [patch 00/14] x86/exceptions: Add guard patches to IST stacks

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Date:   Wed, 3 Apr 2019 18:30:57 +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>
Subject: Re: [patch 00/14] x86/exceptions: Add guard patches to IST stacks

On Sun, 31 Mar 2019, Andy Lutomirski wrote:
> On Sun, Mar 31, 2019 at 3:10 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> > While looking for something different I stumbled over the comment in struct
> > cpu_entry_area:
> >
> >          * Exception stacks used for IST entries.
> >          *
> >          * In the future, this should have a separate slot for each stack
> >          * with guard pages between them.
> >
> > As usual with such comments they are added in good faith and then
> > forgotten. Looking what it takes to fix that let me stumble over some other
> > leftovers like orig_ist[], now unused macros, useless defines and a bunch
> > of assumptions about the exception stacks being a big lump. Aside of that I
> > found a too broad check of the exception stack in the x86/64 stack overflow
> > detector.
> >
> > The following series cleans that up and gradually prepares for guard pages
> > between the IST stacks.
> 
> Thanks!  I'll review this over the next couple days.
> 
> Meanwhile, if you're inspired, I have a WIP series to do the same
> thing to the IRQ stacks here:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=x86/guard_pages
> 
> Want to take a look or pick it up if you want to keep working on this?

I grabbed the lot and addressed the todo's there. Not completely done
though, but it builds and boots :)

With all stacks having guard pages now, the stack_overflow_check() in
irq_64.c is kind of pointless. When the kernel overflows any of the stacks
independent of what we do with DB (we at least split it into 2 different
valid stacks) then it hits a guard page and dies. Mission accomplished....

Thanks,

	tglx