| Message ID | 20201019164932.1430614-1-mic@digikod.net (mailing list archive) |
|---|---|
| Headers | show |
| Series | Add trusted_for(2) (was O_MAYEXEC) | expand |
Andrew, could you please merge this into your tree? On 19/10/2020 18:49, Mickaël Salaün wrote: > Hi, > > Can you please consider to merge this into the tree? > > > Overview > ======== > > The final goal of this patch series is to enable the kernel to be a > global policy manager by entrusting processes with access control at > their level. To reach this goal, two complementary parts are required: > * user space needs to be able to know if it can trust some file > descriptor content for a specific usage; > * and the kernel needs to make available some part of the policy > configured by the system administrator. > > Primary goal of trusted_for(2) > ============================== > > This new syscall enables user space to ask the kernel: is this file > descriptor's content trusted to be used for this purpose? The set of > usage currently only contains "execution", but other may follow (e.g. > "configuration", "sensitive_data"). If the kernel identifies the file > descriptor as trustworthy for this usage, user space should then take > this information into account. The "execution" usage means that the > content of the file descriptor is trusted according to the system policy > to be executed by user space, which means that it interprets the content > or (try to) maps it as executable memory. > > A simple system-wide security policy can be enforced by the system > administrator through a sysctl configuration consistent with the mount > points or the file access rights. The documentation patch explains the > prerequisites. > > It is important to note that this can only enable to extend access > control managed by the kernel. Hence it enables current access control > mechanism to be extended and become a superset of what they can > currently control. Indeed, the security policy could also be delegated > to an LSM, either a MAC system or an integrity system. For instance, > this is required to close a major IMA measurement/appraisal interpreter > integrity gap by bringing the ability to check the use of scripts [1]. > Other uses are expected, such as for magic-links [2], SGX integration > [3], bpffs [4]. > > Complementary W^X protections can be brought by SELinux, IPE [5] and > trampfd [6]. > > Prerequisite of its use > ======================= > > User space needs to adapt to take advantage of this new feature. For > example, the PEP 578 [7] (Runtime Audit Hooks) enables Python 3.8 to be > extended with policy enforcement points related to code interpretation, > which can be used to align with the PowerShell audit features. > Additional Python security improvements (e.g. a limited interpreter > without -c, stdin piping of code) are on their way [8]. > > Examples > ======== > > The initial idea comes from CLIP OS 4 and the original implementation > has been used for more than 12 years: > https://github.com/clipos-archive/clipos4_doc > Chrome OS has a similar approach: > https://chromium.googlesource.com/chromiumos/docs/+/master/security/noexec_shell_scripts.md > > Userland patches can be found here: > https://github.com/clipos-archive/clipos4_portage-overlay/search?q=O_MAYEXEC > Actually, there is more than the O_MAYEXEC changes (which matches this search) > e.g., to prevent Python interactive execution. There are patches for > Bash, Wine, Java (Icedtea), Busybox's ash, Perl and Python. There are > also some related patches which do not directly rely on O_MAYEXEC but > which restrict the use of browser plugins and extensions, which may be > seen as scripts too: > https://github.com/clipos-archive/clipos4_portage-overlay/tree/master/www-client > > An introduction to O_MAYEXEC was given at the Linux Security Summit > Europe 2018 - Linux Kernel Security Contributions by ANSSI: > https://www.youtube.com/watch?v=chNjCRtPKQY&t=17m15s > The "write xor execute" principle was explained at Kernel Recipes 2018 - > CLIP OS: a defense-in-depth OS: > https://www.youtube.com/watch?v=PjRE0uBtkHU&t=11m14s > See also a first LWN article about O_MAYEXEC and a new one about > trusted_for(2) and its background: > * https://lwn.net/Articles/820000/ > * https://lwn.net/Articles/832959/ > > This patch series can be applied on top of v5.9 . This can be tested > with CONFIG_SYSCTL. I would really appreciate constructive comments on > this patch series. > > Previous series: > https://lore.kernel.org/lkml/20201001170232.522331-1-mic@digikod.net/ > > [1] https://lore.kernel.org/lkml/1544647356.4028.105.camel@linux.ibm.com/ > [2] https://lore.kernel.org/lkml/20190904201933.10736-6-cyphar@cyphar.com/ > [3] https://lore.kernel.org/lkml/CALCETrVovr8XNZSroey7pHF46O=kj_c5D9K8h=z2T_cNrpvMig@mail.gmail.com/ > [4] https://lore.kernel.org/lkml/CALCETrVeZ0eufFXwfhtaG_j+AdvbzEWE0M3wjXMWVEO7pj+xkw@mail.gmail.com/ > [5] https://lore.kernel.org/lkml/20200406221439.1469862-12-deven.desai@linux.microsoft.com/ > [6] https://lore.kernel.org/lkml/20200922215326.4603-1-madvenka@linux.microsoft.com/ > [7] https://www.python.org/dev/peps/pep-0578/ > [8] https://lore.kernel.org/lkml/0c70debd-e79e-d514-06c6-4cd1e021fa8b@python.org/ > > Regards, > > Mickaël Salaün (3): > fs: Add trusted_for(2) syscall implementation and related sysctl > arch: Wire up trusted_for(2) > selftest/interpreter: Add tests for trusted_for(2) policies > > Documentation/admin-guide/sysctl/fs.rst | 50 +++ > arch/alpha/kernel/syscalls/syscall.tbl | 1 + > arch/arm/tools/syscall.tbl | 1 + > arch/arm64/include/asm/unistd.h | 2 +- > arch/arm64/include/asm/unistd32.h | 2 + > arch/ia64/kernel/syscalls/syscall.tbl | 1 + > arch/m68k/kernel/syscalls/syscall.tbl | 1 + > arch/microblaze/kernel/syscalls/syscall.tbl | 1 + > arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + > arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + > arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + > arch/parisc/kernel/syscalls/syscall.tbl | 1 + > arch/powerpc/kernel/syscalls/syscall.tbl | 1 + > arch/s390/kernel/syscalls/syscall.tbl | 1 + > arch/sh/kernel/syscalls/syscall.tbl | 1 + > arch/sparc/kernel/syscalls/syscall.tbl | 1 + > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > arch/xtensa/kernel/syscalls/syscall.tbl | 1 + > fs/open.c | 77 ++++ > include/linux/fs.h | 1 + > include/linux/syscalls.h | 2 + > include/uapi/asm-generic/unistd.h | 4 +- > include/uapi/linux/trusted-for.h | 18 + > kernel/sysctl.c | 12 +- > tools/testing/selftests/Makefile | 1 + > .../testing/selftests/interpreter/.gitignore | 2 + > tools/testing/selftests/interpreter/Makefile | 21 + > tools/testing/selftests/interpreter/config | 1 + > .../selftests/interpreter/trust_policy_test.c | 362 ++++++++++++++++++ > 30 files changed, 567 insertions(+), 4 deletions(-) > create mode 100644 include/uapi/linux/trusted-for.h > create mode 100644 tools/testing/selftests/interpreter/.gitignore > create mode 100644 tools/testing/selftests/interpreter/Makefile > create mode 100644 tools/testing/selftests/interpreter/config > create mode 100644 tools/testing/selftests/interpreter/trust_policy_test.c > > > base-commit: bbf5c979011a099af5dc76498918ed7df445635b >