linux-kernel - Re: [RFC PATCH 1/4] x86/entry/nmi: Switch to the entry stack before switching to the thread stack

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Message-ID: <87bl81h3ih.ffs@nanos.tec.linutronix.de>
Date:   Sun, 20 Jun 2021 00:51:34 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Juergen Gross <jgross@...e.com>,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [RFC PATCH 1/4] x86/entry/nmi: Switch to the entry stack before switching to the thread stack

On Tue, Jun 01 2021 at 14:52, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@...ux.alibaba.com>
>
> Current kernel has no code to enforce data breakpoint not on the thread
> stack.  If there is any data breakpoint on the top area of the thread
> stack, there might be problem.

And because the kernel does not prevent data breakpoints on the thread
stack we need to do more complicated things in the already horrible
entry code instead of just doing the obvious and preventing data
breakpoints on the thread stack?

Confused.

Thanks,

        tglx