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From:   Andy Lutomirski <luto@kernel.org>
Date:   Fri, 16 Mar 2018 20:55:28 +0000
Message-ID: <CALCETrXt9Wc1YVO=v=+J9XaZPOX=wwUJiM30UK59_uBL1arG3w@mail.gmail.com>
Subject: Re: [PATCH 12/31] x86/entry/32: Add PTI cr3 switch to non-NMI
 entry/exit points
To:     Joerg Roedel <joro@8bytes.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Brian Gerst <brgerst@gmail.com>,
        Joerg Roedel <jroedel@suse.de>,
        Waiman Long <longman@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Juergen Gross <jgross@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        David Laight <David.Laight@aculab.com>,
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        "Liguori, Anthony" <aliguori@amazon.com>,
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        Kees Cook <keescook@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
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On Fri, Mar 2, 2018 at 9:10 AM, Joerg Roedel <joro@8bytes.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.