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References: <1518168340-9392-1-git-send-email-joro@8bytes.org>
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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
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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>, Denys Vlasenko <dvlasenk@redhat.com>, Eduardo Valentin <eduval@amazon.com>, Greg KH <gregkh@linuxfoundation.org>, Will Deacon <will.deacon@arm.com>, "Liguori, Anthony" <aliguori@amazon.com>, Daniel Gruss <daniel.gruss@iaik.tugraz.at>, Hugh Dickins <hughd@google.com>, Kees Cook <keescook@google.com>, Andrea Arcangeli <aarcange@redhat.com>, Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>

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.