From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 12.1 \(3445.101.1\)) Subject: =?utf-8?Q?Re=3A_=5BPATCH_0/2=5D_Don=E2=80=99t_leave_executable_TL?= =?utf-8?Q?B_entries_to_freed_pages?= From: Nadav Amit In-Reply-To: <20181128000754.18056-1-rick.p.edgecombe@intel.com> Date: Tue, 27 Nov 2018 17:06:05 -0800 Content-Transfer-Encoding: quoted-printable Message-Id: References: <20181128000754.18056-1-rick.p.edgecombe@intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Rick Edgecombe Cc: akpm@linux-foundation.org, luto@kernel.org, will.deacon@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, naveen.n.rao@linux.vnet.ibm.com, anil.s.keshavamurthy@intel.com, davem@davemloft.net, mhiramat@kernel.org, rostedt@goodmis.org, mingo@redhat.com, ast@kernel.org, daniel@iogearbox.net, jeyu@kernel.org, netdev@vger.kernel.org, ard.biesheuvel@linaro.org, jannh@google.com, kristen@linux.intel.com, dave.hansen@intel.com, deneen.t.dock@intel.com List-ID: > On Nov 27, 2018, at 4:07 PM, Rick Edgecombe = wrote: >=20 > Sometimes when memory is freed via the module subsystem, an executable > permissioned TLB entry can remain to a freed page. If the page is = re-used to > back an address that will receive data from userspace, it can result = in user > data being mapped as executable in the kernel. The root of this = behavior is > vfree lazily flushing the TLB, but not lazily freeing the underlying = pages.=20 >=20 > There are sort of three categories of this which show up across = modules, bpf, > kprobes and ftrace: >=20 > 1. When executable memory is touched and then immediatly freed >=20 > This shows up in a couple error conditions in the module loader and = BPF JIT > compiler. Interesting! Note that this may cause conflict with "x86: avoid W^X being broken = during modules loading=E2=80=9D, which I recently submitted.