linux-kernel - Re: [RFC PATCH V2 4/7] x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush

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Message-ID: <CAJhGHyC82f+=YXYmv8zC=zPxZmk+TW_n+5pjcBE-2T8S9t5K0g@mail.gmail.com>
Date:   Tue, 26 May 2020 12:31:00 +0800
From:   Lai Jiangshan <jiangshanlai+lkml@...il.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [RFC PATCH V2 4/7] x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush_mask

On Tue, May 26, 2020 at 12:21 PM Andy Lutomirski <luto@...nel.org> wrote:
>
> On Mon, May 25, 2020 at 6:42 PM Lai Jiangshan <laijs@...ux.alibaba.com> wrote:
> >
> > The percpu user_pcid_flush_mask is used for CPU entry
> > If a data breakpoint on it, it will cause an unwanted #DB.
> > Protect the full cpu_tlbstate structure to be sure.
> >
> > There are some other percpu data used in CPU entry, but they are
> > either in already-protected cpu_tss_rw or are safe to trigger #DB
> > (espfix_waddr, espfix_stack).
>
> How hard would it be to rework this to have DECLARE_PERCPU_NODEBUG()
> and DEFINE_PERCPU_NODEBUG() or similar?


I don't know, but it is an excellent idea. Although the patchset
protects only 2 or 3 portions of percpu data, but there is many
percpu data used in tracing or kprobe code. They are needed to be
protected too.

Adds CC:
Steven Rostedt <rostedt@...dmis.org>
Masami Hiramatsu <mhiramat@...nel.org>