On 25-Mär 12:24, Kees Cook wrote: > On Wed, Mar 25, 2020 at 04:26:21PM +0100, KP Singh wrote: > > From: KP Singh <kpsingh@xxxxxxxxxx> > > > > # v5 -> v6 > > > > https://lwn.net/Articles/815826/ > > Random question: why the switch to lwn.net from lore URLs? The lore > URLs have been suggested to be the canonical way to refer to kernel > development discussion threads. No real reason apart from the fact these were shoter:) Duly noted for future patches and revisions. Thanks! - KP > > -Kees > > > > > * Updated LSM_HOOK macro to define a default value and cleaned up the > > BPF LSM hook declarations. > > * Added Yonghong's Acks and Kees' Reviewed-by tags. > > * Simplification of the selftest code. > > * Rebase and fixes suggested by Andrii and Yonghong and some other minor > > fixes noticed in internal review. > > > > # v4 -> v5 > > > > https://lwn.net/Articles/813057/ > > > > * Removed static keys and special casing of BPF calls from the LSM > > framework. > > * Initialized the BPF callbacks (nops) as proper LSM hooks. > > * Updated to using the newly introduced BPF_TRAMP_MODIFY_RETURN > > trampolines in https://lkml.org/lkml/2020/3/4/877 > > * Addressed Andrii's feedback and rebased. > > > > # v3 -> v4 > > > > * Moved away from allocating a separate security_hook_heads and adding a > > new special case for arch_prepare_bpf_trampoline to using BPF fexit > > trampolines called from the right place in the LSM hook and toggled by > > static keys based on the discussion in: > > > > https://lore.kernel.org/bpf/CAG48ez25mW+_oCxgCtbiGMX07g_ph79UOJa07h=o_6B6+Q-u5g@xxxxxxxxxxxxxx/ > > > > * Since the code does not deal with security_hook_heads anymore, it goes > > from "being a BPF LSM" to "BPF program attachment to LSM hooks". > > * Added a new test case which ensures that the BPF programs' return value > > is reflected by the LSM hook. > > > > # v2 -> v3 does not change the overall design and has some minor fixes: > > > > * LSM_ORDER_LAST is introduced to represent the behaviour of the BPF LSM > > * Fixed the inadvertent clobbering of the LSM Hook error codes > > * Added GPL license requirement to the commit log > > * The lsm_hook_idx is now the more conventional 0-based index > > * Some changes were split into a separate patch ("Load btf_vmlinux only > > once per object") > > > > https://lore.kernel.org/bpf/20200117212825.11755-1-kpsingh@xxxxxxxxxxxx/ > > > > * Addressed Andrii's feedback on the BTF implementation > > * Documentation update for using generated vmlinux.h to simplify > > programs > > * Rebase > > > > # Changes since v1 > > > > https://lore.kernel.org/bpf/20191220154208.15895-1-kpsingh@xxxxxxxxxxxx > > > > * Eliminate the requirement to maintain LSM hooks separately in > > security/bpf/hooks.h Use BPF trampolines to dynamically allocate > > security hooks > > * Drop the use of securityfs as bpftool provides the required > > introspection capabilities. Update the tests to use the bpf_skeleton > > and global variables > > * Use O_CLOEXEC anonymous fds to represent BPF attachment in line with > > the other BPF programs with the possibility to use bpf program pinning > > in the future to provide "permanent attachment". > > * Drop the logic based on prog names for handling re-attachment. > > * Drop bpf_lsm_event_output from this series and send it as a separate > > patch. > > > > # Motivation > > > > Google does analysis of rich runtime security data to detect and thwart > > threats in real-time. Currently, this is done in custom kernel modules > > but we would like to replace this with something that's upstream and > > useful to others. > > > > The current kernel infrastructure for providing telemetry (Audit, Perf > > etc.) is disjoint from access enforcement (i.e. LSMs). Augmenting the > > information provided by audit requires kernel changes to audit, its > > policy language and user-space components. Furthermore, building a MAC > > policy based on the newly added telemetry data requires changes to > > various LSMs and their respective policy languages. > > > > This patchset allows BPF programs to be attached to LSM hooks This > > facilitates a unified and dynamic (not requiring re-compilation of the > > kernel) audit and MAC policy. > > > > # Why an LSM? > > > > Linux Security Modules target security behaviours rather than the > > kernel's API. For example, it's easy to miss out a newly added system > > call for executing processes (eg. execve, execveat etc.) but the LSM > > framework ensures that all process executions trigger the relevant hooks > > irrespective of how the process was executed. > > > > Allowing users to implement LSM hooks at runtime also benefits the LSM > > eco-system by enabling a quick feedback loop from the security community > > about the kind of behaviours that the LSM Framework should be targeting. > > > > # How does it work? > > > > The patchset introduces a new eBPF (https://docs.cilium.io/en/v1.6/bpf/) > > program type BPF_PROG_TYPE_LSM which can only be attached to LSM hooks. > > Loading and attachment of BPF programs requires CAP_SYS_ADMIN. > > > > The new LSM registers nop functions (bpf_lsm_<hook_name>) as LSM hook > > callbacks. Their purpose is to provide a definite point where BPF > > programs can be attached as BPF_TRAMP_MODIFY_RETURN trampoline programs > > for hooks that return an int, and BPF_TRAMP_FEXIT trampoline programs > > for void LSM hooks. > > > > Audit logs can be written using a format chosen by the eBPF program to > > the perf events buffer or to global eBPF variables or maps and can be > > further processed in user-space. > > > > # BTF Based Design > > > > The current design uses BTF: > > > > * https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html > > * https://lwn.net/Articles/803258 > > > > which allows verifiable read-only structure accesses by field names > > rather than fixed offsets. This allows accessing the hook parameters > > using a dynamically created context which provides a certain degree of > > ABI stability: > > > > > > // Only declare the structure and fields intended to be used > > // in the program > > struct vm_area_struct { > > unsigned long vm_start; > > } __attribute__((preserve_access_index)); > > > > // Declare the eBPF program mprotect_audit which attaches to > > // to the file_mprotect LSM hook and accepts three arguments. > > SEC("lsm/file_mprotect") > > int BPF_PROG(mprotect_audit, struct vm_area_struct *vma, > > unsigned long reqprot, unsigned long prot, int ret) > > { > > unsigned long vm_start = vma->vm_start; > > > > return 0; > > } > > > > By relocating field offsets, BTF makes a large portion of kernel data > > structures readily accessible across kernel versions without requiring a > > large corpus of BPF helper functions and requiring recompilation with > > every kernel version. The BTF type information is also used by the BPF > > verifier to validate memory accesses within the BPF program and also > > prevents arbitrary writes to the kernel memory. > > > > The limitations of BTF compatibility are described in BPF Co-Re > > (http://vger.kernel.org/bpfconf2019_talks/bpf-core.pdf, i.e. field > > renames, #defines and changes to the signature of LSM hooks). This > > design imposes that the MAC policy (eBPF programs) be updated when the > > inspected kernel structures change outside of BTF compatibility > > guarantees. In practice, this is only required when a structure field > > used by a current policy is removed (or renamed) or when the used LSM > > hooks change. We expect the maintenance cost of these changes to be > > acceptable as compared to the design presented in the RFC. > > > > (https://lore.kernel.org/bpf/20190910115527.5235-1-kpsingh@xxxxxxxxxxxx/). > > > > # Usage Examples > > > > A simple example and some documentation is included in the patchset. > > In order to better illustrate the capabilities of the framework some > > more advanced prototype (not-ready for review) code has also been > > published separately: > > > > * Logging execution events (including environment variables and > > arguments) > > https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_audit_env.c > > > > * Detecting deletion of running executables: > > https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_detect_exec_unlink.c > > > > * Detection of writes to /proc/<pid>/mem: > > https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_audit_env.c > > > > We have updated Google's internal telemetry infrastructure and have > > started deploying this LSM on our Linux Workstations. This gives us more > > confidence in the real-world applications of such a system. > > > > > > KP Singh (8): > > bpf: Introduce BPF_PROG_TYPE_LSM > > security: Refactor declaration of LSM hooks > > bpf: lsm: provide attachment points for BPF LSM programs > > bpf: lsm: Implement attach, detach and execution > > bpf: lsm: Initialize the BPF LSM hooks > > tools/libbpf: Add support for BPF_PROG_TYPE_LSM > > bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM > > bpf: lsm: Add Documentation > > > > Documentation/bpf/bpf_lsm.rst | 150 +++++ > > Documentation/bpf/index.rst | 1 + > > MAINTAINERS | 1 + > > include/linux/bpf.h | 3 + > > include/linux/bpf_lsm.h | 32 + > > include/linux/bpf_types.h | 4 + > > include/linux/lsm_hook_defs.h | 378 +++++++++++ > > include/linux/lsm_hooks.h | 627 +----------------- > > include/uapi/linux/bpf.h | 2 + > > init/Kconfig | 10 + > > kernel/bpf/Makefile | 1 + > > kernel/bpf/bpf_lsm.c | 60 ++ > > kernel/bpf/btf.c | 9 +- > > kernel/bpf/syscall.c | 56 +- > > kernel/bpf/trampoline.c | 17 +- > > kernel/bpf/verifier.c | 19 +- > > kernel/trace/bpf_trace.c | 12 +- > > security/Kconfig | 10 +- > > security/Makefile | 2 + > > security/bpf/Makefile | 5 + > > security/bpf/hooks.c | 26 + > > security/security.c | 432 ++++++------ > > tools/include/uapi/linux/bpf.h | 2 + > > tools/lib/bpf/bpf.c | 3 +- > > tools/lib/bpf/libbpf.c | 39 +- > > tools/lib/bpf/libbpf.h | 4 + > > tools/lib/bpf/libbpf.map | 3 + > > tools/lib/bpf/libbpf_probes.c | 1 + > > tools/testing/selftests/bpf/config | 2 + > > tools/testing/selftests/bpf/lsm_helpers.h | 19 + > > .../selftests/bpf/prog_tests/lsm_test.c | 112 ++++ > > .../selftests/bpf/progs/lsm_int_hook.c | 54 ++ > > .../selftests/bpf/progs/lsm_void_hook.c | 41 ++ > > 33 files changed, 1277 insertions(+), 860 deletions(-) > > create mode 100644 Documentation/bpf/bpf_lsm.rst > > create mode 100644 include/linux/bpf_lsm.h > > create mode 100644 include/linux/lsm_hook_defs.h > > create mode 100644 kernel/bpf/bpf_lsm.c > > create mode 100644 security/bpf/Makefile > > create mode 100644 security/bpf/hooks.c > > create mode 100644 tools/testing/selftests/bpf/lsm_helpers.h > > create mode 100644 tools/testing/selftests/bpf/prog_tests/lsm_test.c > > create mode 100644 tools/testing/selftests/bpf/progs/lsm_int_hook.c > > create mode 100644 tools/testing/selftests/bpf/progs/lsm_void_hook.c > > > > -- > > 2.20.1 > > > > -- > Kees Cook
