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Date:   Wed, 20 Feb 2019 09:47:05 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Jann Horn <jannh@google.com>
Cc:     Masami Hiramatsu <mhiramat@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
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        Changbin Du <changbin.du@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access
 kernel memory that can fault
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On Wed, 20 Feb 2019 14:57:31 +0100
Jann Horn <jannh@google.com> wrote:

> > (*) BTW, there is another concern to use _from_user APIs in kprobe. Are those
> > APIs might sleep??  
> 
> If you want to access userspace without sleeping, and ignore data in
> non-present pages, you can do `pagefault_disable(); err =
> __copy_from_user_inatomic(...); pagefault_enable();`. (Actually, maybe
> the kernel should have a helper for that...)

I was about to say pretty much the same thing (about using
_inatomic()), but yeah, we should also have a helper function if we
don't already to include the page_fault_disable/enable() too.

-- Steve