Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
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>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        stable <stable@vger.kernel.org>,
        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
Message-ID: <20190220094705.21ffbf51@gandalf.local.home>
In-Reply-To: <CAG48ez0e5b0qmW1kMVEYDKvxn=-FkfRw=0KXUm5_R3aAGU-LJA@mail.gmail.com>
References: <20190215174712.372898450@goodmis.org>
        <20190215174945.557218316@goodmis.org>
        <CAHk-=wjP4bEYCFaKZVG4kLWmYBctyfsW9jjhC91tiTk9WwB8Rg@mail.gmail.com>
        <20190215171539.4682f0b4@gandalf.local.home>
        <300C4516-A093-43AE-8707-1C42486807A4@amacapital.net>
        <20190215191949.04604191@gandalf.local.home>
        <CAHk-=wgJzNp0R3cVhjBPHTR4X9sOvHdqK4UVFfbsOKQ6L=A_eQ@mail.gmail.com>
        <CAHk-=wh9XrOykA5J9RQ7zaBio-S_D+1AE+rGnBYWSd==pCXh+w@mail.gmail.com>
        <20190219111802.1d6dbaa3@gandalf.local.home>
        <CAHk-=wgTuK3kAduP-gr10vykT1uG=B2VpdffvmyBuTQ1UxPpMg@mail.gmail.com>
        <20190219140330.5dd9e876@gandalf.local.home>
        <20190220171019.5e81a4946b56982f324f7c45@kernel.org>
        <CAG48ez0e5b0qmW1kMVEYDKvxn=-FkfRw=0KXUm5_R3aAGU-LJA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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