linux-kernel - Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault

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Message-ID: <CALCETrVDMhpA-oJnpuEP2j21aK5ZosW2PNskVDxm4MSR6Afqug@mail.gmail.com>
Date:   Sat, 23 Feb 2019 20:38:03 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable <stable@...r.kernel.org>,
        Changbin Du <changbin.du@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access
 kernel memory that can fault

On Sat, Feb 23, 2019 at 4:44 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Sat, 23 Feb 2019 12:47:46 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> > Since kprobes handler runs in IRQ context, we can not use access_ok() in it.
> > (only on x86 + CONFIG_DEBUG_ATOMIC_SLEEP=y)
>
> Is it really IRQ context or exception context? That is, one
> (interrupts) happen for any task, but exceptions happen because of the
> software that is executed (like a breakpoint). Although you can have a
> kprobe trigger in an interrupt handler (where user access wouldn't make
> sense anyway). But there should be no problem with user access from an
> exception handler.
>

Can we just get rid of this might_sleep()?  access_ok() doesn't sleep
as far as I know.