linux-kernel - Re: [patch V4 part 1 02/36] x86/hw_breakpoint: Prevent data breakpoints on cpu_entry

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Message-ID: <CALCETrVSNPQesBfuKVwZkQXTF-Q-p4s6jH8ocr0RKRErERRzMA@mail.gmail.com>
Date:   Sat, 9 May 2020 12:08:38 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Lai Jiangshan <jiangshanlai+lkml@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V4 part 1 02/36] x86/hw_breakpoint: Prevent data
 breakpoints on cpu_entry_area

On Sat, May 9, 2020 at 2:23 AM Lai Jiangshan
<jiangshanlai+lkml@...il.com> wrote:
>
> On Tue, May 5, 2020 at 10:15 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > From: Andy Lutomirski <luto@...nel.org>
> >
> > A data breakpoint near the top of an IST stack will cause unresoverable
> > recursion.  A data breakpoint on the GDT, IDT, or TSS is terrifying.
> > Prevent either of these from happening.
> >
>
> What happen when a data breakpoint on the direct GDT (load_direct_gdt())
> and the debug IDT (load_debug_idt()) which are not considered in this patch?
>

I have no idea, and learning the answer may involve talking to the
respective CPU vendors' microcode engineers.  We should probably block
those, too.