linux-kernel - Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI entry/exit points

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Date:   Fri, 16 Mar 2018 20:55:28 +0000
From:   Andy Lutomirski <luto@...nel.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Joerg Roedel <jroedel@...e.de>,
        Waiman Long <longman@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI
 entry/exit points

On Fri, Mar 2, 2018 at 9:10 AM, Joerg Roedel <joro@...tes.org> wrote:
> On Thu, Mar 01, 2018 at 10:38:21AM -0800, Linus Torvalds wrote:
>> Note that debug traps can happen regardless of TF, Think kgdb etc.
>> Arguably kgdb users get what they deserve, but still.. I think root
>> can set kernel breakpoints too.
>
> But that seems to be broken right now at least wrt. to the espfix code
> where there is no handling for in the #DB handler. Can userspace really
> set arbitrary kernel breakpoints?
>

As far as I'm concerned, I don't try to support kernel debugger users
setting arbitrary breakpoints in the kernel entry text.