From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f200.google.com (mail-pl1-f200.google.com [209.85.214.200]) by kanga.kvack.org (Postfix) with ESMTP id 494956B6C27 for ; Mon, 3 Dec 2018 20:43:16 -0500 (EST) Received: by mail-pl1-f200.google.com with SMTP id d23so11391506plj.22 for ; Mon, 03 Dec 2018 17:43:16 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id e40sor20442705plb.21.2018.12.03.17.43.14 for (Google Transport Security); Mon, 03 Dec 2018 17:43:14 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 12.1 \(3445.101.1\)) Subject: Re: [PATCH 1/2] vmalloc: New flag for flush before releasing pages From: Nadav Amit In-Reply-To: <20181128000754.18056-2-rick.p.edgecombe@intel.com> Date: Mon, 3 Dec 2018 17:43:11 -0800 Content-Transfer-Encoding: quoted-printable Message-Id: <4883FED1-D0EC-41B0-A90F-1A697756D41D@gmail.com> References: <20181128000754.18056-1-rick.p.edgecombe@intel.com> <20181128000754.18056-2-rick.p.edgecombe@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Rick Edgecombe Cc: Andrew Morton , Andy Lutomirski , Will Deacon , linux-mm , LKML , Kernel Hardening , naveen.n.rao@linux.vnet.ibm.com, anil.s.keshavamurthy@intel.com, David Miller , Masami Hiramatsu , Steven Rostedt , Ingo Molnar , ast@kernel.org, Daniel Borkmann , jeyu@kernel.org, netdev@vger.kernel.org, Ard Biesheuvel , Jann Horn , kristen@linux.intel.com, Dave Hansen , deneen.t.dock@intel.com, Peter Zijlstra > On Nov 27, 2018, at 4:07 PM, Rick Edgecombe = wrote: >=20 > Since vfree will lazily flush the TLB, but not lazily free the = underlying pages, > it often leaves stale TLB entries to freed pages that could get = re-used. This is > undesirable for cases where the memory being freed has special = permissions such > as executable. So I am trying to finish my patch-set for preventing transient W+X = mappings from taking space, by handling kprobes & ftrace that I missed (thanks = again for pointing it out). But all of the sudden, I don=E2=80=99t understand why we have the = problem that this (your) patch-set deals with at all. We already change the mappings to = make the memory writable before freeing the memory, so why can=E2=80=99t we = make it non-executable at the same time? Actually, why do we make the module = memory, including its data executable before freeing it??? In other words: disable_ro_nx() is called by free_module() before = freeing the memory. Wouldn=E2=80=99t inverting the logic makes much more sense? = I am confused. -- >8 -- From: Nadav Amit Subject: [PATCH] modules: disable_ro_nx() should enable nx=20 --- kernel/module.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/kernel/module.c b/kernel/module.c index 7cb207249437..e12d760ea3b0 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -2029,14 +2029,13 @@ void set_all_modules_text_ro(void) =20 static void disable_ro_nx(const struct module_layout *layout) { + frob_text(layout, set_memory_nx); + if (rodata_enabled) { frob_text(layout, set_memory_rw); frob_rodata(layout, set_memory_rw); frob_ro_after_init(layout, set_memory_rw); } - frob_rodata(layout, set_memory_x); - frob_ro_after_init(layout, set_memory_x); - frob_writable_data(layout, set_memory_x); } =20 #else --=20 2.17.1