On 08/06/2023 10:42, Zachary Leaf wrote:
Hi,
After getting side tracked by eBPF libraries/tools (libbpf/bpftool) and kselftest cross-compilation, here's the core kernel changes following on from the RFC[1] posted late last year.
The bpf syscall is updated to propagate user pointers as capabilities in the pure-capability kernel-user ABI (PCuABI). It also includes an approach to support the existing aarch64 ABI as a compatibility layer (compat64).
One complication here is from the fact this syscall supports many multiplexed sub-commands, some of which are themselves multiplexed with a number of nested multiplexed options.
A further complication is that the existing syscall uses a trick of storing user pointers as u64 to avoid needing a compat handler for 32-bit systems (see patch 3). To retain compatibility with the aarch64 ABI and add Morello support, a compat layer is added here only for the compat64 case, guarded by #ifdef CONFIG_COMPAT64. Normal compat32 operation is therefore unchanged.
Compared to the original RFC, inbound (userspace->kernel) conversion between compat64/native struct layouts is now handled upfront. This minimises changes to subcommand handlers. Some subcommands require conversion back out to userspace and that is by necessity handled where it occurs.
Patch 1 is not essential to this series but it's a nice debug feature to have and works[2]. It enables BPF_PROG_TYPE_TRACEPOINT which many eBPF kselftests use.
Patch 2 is required setup for the rest of the patches.
Patches 3-8 implement the core compat64 handling. Each commit compiles cleanly but relevant parts will be broken inbetween. They're split mainly to make review here easier.
Patch 9 fixes a check to also check configs passed in via compat64.
Patch 10 finally enables capabilities in the kernel.
Nice work! Kudos for the commit messages (and that cover letter), I really appreciate the effort put into writing those.
I have mostly looked at the patches from a functional perspective, without going into the details of each subcommand / field at this stage (I don't expect major issues there anyway). Overall the approach looks good, I think the chosen trade-offs make sense. I've got a number of specific comments/questions as usual, inline in each patch.
Cheers, Kevin
Testing wise, see associated LTP changes below which will be posted to linux-morello-ltp mailing list. The eBPF LTP tests are fairly minimal and test only a small part of the changes here. There's a new test to test patch 9.
The kernel kselftests contain much more extensive eBPF tests. The kselftests have been used to test many parts of the compat64 handling but overall more work needs to be done here: a) enable cross-compilation for purecap as well as x86->aarch64 b) replace ptr_to_u64() with casts to uintptr_t in tests b) general libbpf/bpftool enablement and fixes since many tests rely on this c) CONFIG_DEBUG_INFO_BTF required for many tests but this requires the build system to have a recent version of pahole tool
Next steps once we have the core kernel support is porting libbpf and bpftool for purecap plus work on enabling kselftests as above.
Kernel branch available at: https://git.morello-project.org/zdleaf/linux/-/tree/morello/bpf
Associated LTP test/changes at: https://git.morello-project.org/zdleaf/morello-linux-test-project/-/tree/mor...
Thanks,
Zach
[1] [RFC PATCH 0/9] update bpf syscall for PCuABI/compat64 https://op-lists.linaro.org/archives/list/linux-morello@op-lists.linaro.org/... [2] [PATCH v3 0/5] Restore syscall tracing on Morello https://op-lists.linaro.org/archives/list/linux-morello@op-lists.linaro.org/...
Zachary Leaf (10): arm64: morello: enable syscall tracing bpf/net: copy ptrs from user with bpf/sockptr_t bpf: compat64: add handler and convert bpf_attr in bpf: compat64: bpf_attr convert out bpf: compat64: handle bpf_btf_info bpf: compat64: handle bpf_prog_info bpf: compat64: handle bpf_map_info bpf: compat64: handle bpf_link_info bpf: compat64: support CHECK_ATTR macro bpf: use user pointer types in uAPI structs
.../morello_transitional_pcuabi_defconfig | 2 +- arch/arm64/kernel/sys_compat64.c | 4 + drivers/media/rc/bpf-lirc.c | 7 +- include/linux/bpf_compat.h | 413 ++++++ include/linux/bpfptr.h | 18 +- include/linux/sockptr.h | 9 + include/uapi/linux/bpf.h | 94 +- kernel/bpf/bpf_iter.c | 2 +- kernel/bpf/btf.c | 97 +- kernel/bpf/cgroup.c | 10 +- kernel/bpf/hashtab.c | 13 +- kernel/bpf/net_namespace.c | 7 +- kernel/bpf/offload.c | 2 +- kernel/bpf/syscall.c | 1136 +++++++++++++---- kernel/bpf/verifier.c | 2 +- kernel/trace/bpf_trace.c | 6 +- net/bpf/bpf_dummy_struct_ops.c | 3 +- net/bpf/test_run.c | 32 +- net/core/sock_map.c | 7 +- 19 files changed, 1534 insertions(+), 330 deletions(-) create mode 100644 include/linux/bpf_compat.h
-- 2.34.1
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