Re: [PATCH bpf-next] bpf: Make trampolines W^X

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Justin Capella <justincapella@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Rick Edgecombe <rick.p.edgecombe@intel.com>,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	x86@kernel.org, linux-security-module@vger.kernel.org,
	Kees Cook <keescook@chromium.org>,
	"David S. Miller" <davem@davemloft.net>,
	Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	Thomas Garnier <thgarnie@chromium.org>,
	Florent Revest <revest@chromium.org>,
	Brendan Jackman <jackmanb@chromium.org>,
	Jann Horn <jannh@google.com>, Matthew Garrett <mjg59@google.com>,
	Michael Halcrow <mhalcrow@google.com>
Subject: Re: [PATCH bpf-next] bpf: Make trampolines W^X
Date: Tue, 7 Jan 2020 10:55:33 -0800	[thread overview]
Message-ID: <20200107185532.4zax5j5ln456u7rj@ast-mbp> (raw)
In-Reply-To: <20200107091132.GR2844@hirez.programming.kicks-ass.net>

On Tue, Jan 07, 2020 at 10:11:32AM +0100, Peter Zijlstra wrote:
> On Mon, Jan 06, 2020 at 02:13:18PM -0800, Alexei Starovoitov wrote:
> > On Sun, Jan 05, 2020 at 10:33:54AM +0900, Andy Lutomirski wrote:
> > > 
> > > >> On Jan 4, 2020, at 8:03 PM, Justin Capella <justincapella@gmail.com> wrote:
> > > > 
> > > > I'm rather ignorant about this topic but it would make sense to check prior to making executable from a security standpoint wouldn't it? (In support of the (set_memory_ro + set_memory_x)
> > > > 
> > > 
> > > Maybe, depends if it’s structured in a way that’s actually helpful from a security perspective.
> > > 
> > > It doesn’t help that set_memory_x and friends are not optimized at all. These functions are very, very, very slow and adversely affect all CPUs.
> > 
> > That was one of the reason it wasn't done in the first.
> > Also ftrace trampoline break w^x as well.
> 
> Didn't I fix that?

yes. in the tip. many months ago. that's why up-thread I was saying that I'm
waiting for all text_poke[_bp] patches to land upstream and do the same thing
for bpf trampoline and bpf dispatcher (which has the same issue).