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: <20190220094705.21ffbf51@gandalf.local.home>
Date:   Wed, 20 Feb 2019 09:47:05 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        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>,
        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 Wed, 20 Feb 2019 14:57:31 +0100
Jann Horn <jannh@...gle.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