From: jeffxu@chromium.org
To: skhan@linuxfoundation.org, keescook@chromium.org
Cc: akpm@linux-foundation.org, dmitry.torokhov@gmail.com,
dverkamp@chromium.org, hughd@google.com, jeffxu@google.com,
jorgelo@chromium.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
jannh@google.com, linux-hardening@vger.kernel.org,
Jeff Xu <jeffxu@chromium.org>
Subject: [PATCH v5 0/6] mm/memfd: introduce MFD_NOEXEC_SEAL and MFD_EXEC
Date: Tue, 6 Dec 2022 15:23:52 +0000 [thread overview]
Message-ID: <20221206152358.1966099-1-jeffxu@google.com> (raw)
From: Jeff Xu <jeffxu@chromium.org>
Since Linux introduced the memfd feature, memfd have always had their execute bit set, and the memfd_create() syscall doesn't allow setting it differently.
However, in a secure by default system, such as ChromeOS, (where all executables should come from the rootfs, which is protected by Verified boot), this executable nature of memfd opens a door for NoExec bypass and enables “confused deputy attack”. E.g, in VRP bug [1]: cros_vm process created a memfd to share the content with an external process, however the memfd is overwritten and used for executing arbitrary code and root escalation. [2] lists more VRP in this kind.
On the other hand, executable memfd has its legit use, runc uses memfd’s seal and executable feature to copy the contents of the binary then execute them, for such system, we need a solution to differentiate runc's use of executable memfds and an attacker's [3].
To address those above, this set of patches add following:
1> Let memfd_create() set X bit at creation time.
2> Let memfd to be sealed for modifying X bit.
3> A new pid namespace sysctl: vm.memfd_noexec to control behavior of X bit. For example, if a container has vm.memfd_noexec=2, then memfd_create() without MFD_NOEXEC_SEAL will be rejected.
4> A new security hook in memfd_create(). This make it possible to a new LSM, which rejects or allows executable memfd based on its security policy.
This is V4 version of patch: see [4] [5] [6] for previous versions.
[1] https://crbug.com/1305411
[2] https://bugs.chromium.org/p/chromium/issues/list?q=type%3Dbug-security%20memfd%20escalation&can=1
[3] https://lwn.net/Articles/781013/
[4] https://lwn.net/Articles/890096/
[5] https://lore.kernel.org/lkml/20220805222126.142525-1-jeffxu@chromium.org/
[6] https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@chromium.org/
Daniel Verkamp (2):
mm/memfd: add F_SEAL_EXEC
selftests/memfd: add tests for F_SEAL_EXEC
Jeff Xu (4):
mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC
mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd
selftests/memfd: add tests for MFD_NOEXEC_SEAL MFD_EXEC
mm/memfd: security hook for memfd_create
include/linux/lsm_hook_defs.h | 1 +
include/linux/lsm_hooks.h | 4 +
include/linux/pid_namespace.h | 19 ++
include/linux/security.h | 6 +
include/uapi/linux/fcntl.h | 1 +
include/uapi/linux/memfd.h | 4 +
kernel/pid_namespace.c | 48 ++++
mm/memfd.c | 61 ++++-
mm/shmem.c | 6 +
security/security.c | 13 +
tools/testing/selftests/memfd/fuse_test.c | 1 +
tools/testing/selftests/memfd/memfd_test.c | 304 ++++++++++++++++++++-
12 files changed, 465 insertions(+), 3 deletions(-)
base-commit: eb7081409f94a9a8608593d0fb63a1aa3d6f95d8
--
2.39.0.rc0.267.gcb52ba06e7-goog
next reply other threads:[~2022-12-06 15:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-06 15:23 jeffxu [this message]
2022-12-06 15:23 ` [PATCH v5 1/6] mm/memfd: add F_SEAL_EXEC jeffxu
2022-12-06 15:23 ` [PATCH v5 2/6] selftests/memfd: add tests for F_SEAL_EXEC jeffxu
2022-12-06 15:23 ` [PATCH v5 3/6] mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC jeffxu
2022-12-06 16:04 ` Greg KH
2022-12-06 16:26 ` Jeff Xu
2022-12-06 16:35 ` Greg KH
2022-12-06 17:48 ` Jeff Xu
2022-12-06 23:24 ` Kees Cook
2022-12-06 15:23 ` [PATCH v5 4/6] mm/memfd: Add write seals when apply SEAL_EXEC to executable memfd jeffxu
2022-12-06 15:23 ` [PATCH v5 5/6] selftests/memfd: add tests for MFD_NOEXEC_SEAL MFD_EXEC jeffxu
2022-12-06 16:02 ` Greg KH
2022-12-06 15:23 ` [PATCH v5 6/6] mm/memfd: security hook for memfd_create jeffxu
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