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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 <nadav.amit@gmail.com>
In-Reply-To: <20181128000754.18056-1-rick.p.edgecombe@intel.com>
Date:   Tue, 27 Nov 2018 17:06:05 -0800
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References: <20181128000754.18056-1-rick.p.edgecombe@intel.com>
To:     Rick Edgecombe <rick.p.edgecombe@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Nov 27, 2018, at 4:07 PM, Rick Edgecombe =
<rick.p.edgecombe@intel.com> 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.