| Message ID | 20221207154939.2532830-1-jeffxu@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | mm/memfd: introduce MFD_NOEXEC_SEAL and MFD_EXEC | expand |
On Wed, Dec 07, 2022 at 03:49:33PM +0000, jeffxu@chromium.org wrote: > This is V6 version of patch: see [4] [5] [6] [7] for previous versions. When sending a new version, can you include an overview of what changed between this version and the prior version? This helps reviewers who are following along, so it's easier to focus our attention on the differences. Also, it's helpful to version the links: > [4] https://lwn.net/Articles/890096/ > [5] https://lore.kernel.org/lkml/20220805222126.142525-1-jeffxu@google.com/ > [6] https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@google.com/ > [7] https://lore.kernel.org/lkml/20221206152358.1966099-1-jeffxu@google.com/ e.g.: v6: - moved foo to bar - improve comments for baz v5: https://lore.kernel.org/lkml/20221206152358.1966099-1-jeffxu@google.com/ v3: https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@google.com/ v2: ...etc -Kees
On Thu, Dec 8, 2022 at 8:13 AM Kees Cook <keescook@chromium.org> wrote: > > On Wed, Dec 07, 2022 at 03:49:33PM +0000, jeffxu@chromium.org wrote: > > This is V6 version of patch: see [4] [5] [6] [7] for previous versions. > > When sending a new version, can you include an overview of what changed > between this version and the prior version? This helps reviewers who are > following along, so it's easier to focus our attention on the > differences. Also, it's helpful to version the links: > > > [4] https://lwn.net/Articles/890096/ > > [5] https://lore.kernel.org/lkml/20220805222126.142525-1-jeffxu@google.com/ > > [6] https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@google.com/ > > [7] https://lore.kernel.org/lkml/20221206152358.1966099-1-jeffxu@google.com/ > > e.g.: > > v6: > - moved foo to bar > - improve comments for baz > v5: https://lore.kernel.org/lkml/20221206152358.1966099-1-jeffxu@google.com/ > v3: https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@google.com/ > v2: ...etc > Will do! Much appreciated for helping me through the process of my first patch in the kernel. Jeff > -Kees > > -- > Kees Cook
On Thu, Dec 08, 2022 at 10:33:19AM -0800, Jeff Xu wrote: > On Thu, Dec 8, 2022 at 8:13 AM Kees Cook <keescook@chromium.org> wrote: > > > > On Wed, Dec 07, 2022 at 03:49:33PM +0000, jeffxu@chromium.org wrote: > > > This is V6 version of patch: see [4] [5] [6] [7] for previous versions. > > > > When sending a new version, can you include an overview of what changed > > between this version and the prior version? This helps reviewers who are > > following along, so it's easier to focus our attention on the > > differences. Also, it's helpful to version the links: > > > > > [4] https://lwn.net/Articles/890096/ > > > [5] https://lore.kernel.org/lkml/20220805222126.142525-1-jeffxu@google.com/ > > > [6] https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@google.com/ > > > [7] https://lore.kernel.org/lkml/20221206152358.1966099-1-jeffxu@google.com/ > > > > e.g.: > > > > v6: > > - moved foo to bar > > - improve comments for baz > > v5: https://lore.kernel.org/lkml/20221206152358.1966099-1-jeffxu@google.com/ > > v3: https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@google.com/ > > v2: ...etc > > > Will do! > Much appreciated for helping me through the process of my first patch > in the kernel. Happy to help! I'm excited to see this gap in memfd security closed. :)
From: Jeff Xu <jeffxu@google.com> 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 the 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 V6 version of patch: see [4] [5] [6] [7] 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@google.com/ [6] https://lore.kernel.org/lkml/20221202013404.163143-1-jeffxu@google.com/ [7] https://lore.kernel.org/lkml/20221206152358.1966099-1-jeffxu@google.com/ 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 | 5 + kernel/pid_sysctl.h | 59 ++++ 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 | 348 ++++++++++++++++++++- 13 files changed, 525 insertions(+), 3 deletions(-) create mode 100644 kernel/pid_sysctl.h base-commit: eb7081409f94a9a8608593d0fb63a1aa3d6f95d8