Status of the patches ===================== Thanks for the reviews! There's one review comment from John which I haven't resolved [3]. He pointed out that we could make the verifier a bit smarter about propagating register bounds. I don't have a clear picture of how useful it would be but IIUC it would be quite simple (see my reply to the linked mail with a proposed implementation). Differences from v4->v5 [1]: * Fixed bogus type casts in interpreter that led to warnings from the 0day robot. * Dropped feature-detection for Clang per Andrii's suggestion in [4]. The selftests will now fail to build unless you have llvm-project commit 286daafd6512. The ENABLE_ATOMICS_TEST macro is still needed to support the no_alu32 tests. * Carried some Acks from John and Yonghong. * Dropped confusing usage of __atomic_exchange from prog_test in favour of __sync_lock_test_and_set. * [Really] got rid of all the forest of instruction macros (BPF_ATOMIC_FETCH_ADD and friends); now there's just BPF_ATOMIC_OP to define all the instructions as we use them in the verifier tests. This makes the atomic ops less special in that API, and I don't think the resulting usage is actually any harder to read. Differences from v3->v4 [1]: * Added one Ack from Yonghong. He acked some other patches but those have now changed non-trivally so I didn't add those acks. * Fixups to commit messages. * Fixed disassembly and comments: first arg to atomic_fetch_* is a pointer. * Improved prog_test efficiency. BPF progs are now all loaded in a single call, then the skeleton is re-used for each subtest. * Dropped use of tools/build/feature in favour of a one-liner in the Makefile. * Dropped the commit that created an emit_neg helper in the x86 JIT. It's not used any more (it wasn't used in v3 either). * Combined all the different filter.h macros (used to be BPF_ATOMIC_ADD, BPF_ATOMIC_FETCH_ADD, BPF_ATOMIC_AND, etc) into just BPF_ATOMIC32 and BPF_ATOMIC64. * Removed some references to BPF_STX_XADD from tools/, samples/ and lib/ that I missed before. Differences from v2->v3 [1]: * More minor fixes and naming/comment changes * Dropped atomic subtract: compilers can implement this by preceding an atomic add with a NEG instruction (which is what the x86 JIT did under the hood anyway). * Dropped the use of -mcpu=v4 in the Clang BPF command-line; there is no longer an architecture version bump. Instead a feature test is added to Kbuild - it builds a source file to check if Clang supports BPF atomics. * Fixed the prog_test so it no longer breaks test_progs-no_alu32. This requires some ifdef acrobatics to avoid complicating the prog_tests model where the same userspace code exercises both the normal and no_alu32 BPF test objects, using the same skeleton header. Differences from v1->v2 [1]: * Fixed mistakes in the netronome driver * Addd sub, add, or, xor operations * The above led to some refactors to keep things readable. (Maybe I should have just waited until I'd implemented these before starting the review...) * Replaced BPF_[CMP]SET | BPF_FETCH with just BPF_[CMP]XCHG, which include the BPF_FETCH flag * Added a bit of documentation. Suggestions welcome for more places to dump this info... The prog_test that's added depends on Clang/LLVM features added by Yonghong in commit 286daafd6512 (was https://reviews.llvm.org/D72184). This only includes a JIT implementation for x86_64 - I don't plan to implement JIT support myself for other architectures. Operations ========== This patchset adds atomic operations to the eBPF instruction set. The use-case that motivated this work was a trivial and efficient way to generate globally-unique cookies in BPF progs, but I think it's obvious that these features are pretty widely applicable. The instructions that are added here can be summarised with this list of kernel operations: * atomic[64]_[fetch_]add * atomic[64]_[fetch_]and * atomic[64]_[fetch_]or * atomic[64]_xchg * atomic[64]_cmpxchg The following are left out of scope for this effort: * 16 and 8 bit operations * Explicit memory barriers Encoding ======== I originally planned to add new values for bpf_insn.opcode. This was rather unpleasant: the opcode space has holes in it but no entire instruction classes[2]. Yonghong Song had a better idea: use the immediate field of the existing STX XADD instruction to encode the operation. This works nicely, without breaking existing programs, because the immediate field is currently reserved-must-be-zero, and extra-nicely because BPF_ADD happens to be zero. Note that this of course makes immediate-source atomic operations impossible. It's hard to imagine a measurable speedup from such instructions, and if it existed it would certainly not benefit x86, which has no support for them. The BPF_OP opcode fields are re-used in the immediate, and an additional flag BPF_FETCH is used to mark instructions that should fetch a pre-modification value from memory. So, BPF_XADD is now called BPF_ATOMIC (the old name is kept to avoid breaking userspace builds), and where we previously had .imm = 0, we now have .imm = BPF_ADD (which is 0). Operands ======== Reg-source eBPF instructions only have two operands, while these atomic operations have up to four. To avoid needing to encode additional operands, then: - One of the input registers is re-used as an output register (e.g. atomic_fetch_add both reads from and writes to the source register). - Where necessary (i.e. for cmpxchg) , R0 is "hard-coded" as one of the operands. This approach also allows the new eBPF instructions to map directly to single x86 instructions. [1] Previous iterations: v1: https://lore.kernel.org/bpf/20201123173202.1335708-1-jackmanb@xxxxxxxxxx/ v2: https://lore.kernel.org/bpf/20201127175738.1085417-1-jackmanb@xxxxxxxxxx/ v3: https://lore.kernel.org/bpf/X8kN7NA7bJC7aLQI@xxxxxxxxxx/ v4: https://lore.kernel.org/bpf/20201207160734.2345502-1-jackmanb@xxxxxxxxxx/ [2] Visualisation of eBPF opcode space: https://gist.github.com/bjackman/00fdad2d5dfff601c1918bc29b16e778 [3] Comment from John about propagating bounds in verifier: https://lore.kernel.org/bpf/5fcf0fbcc8aa8_9ab320853@john-XPS-13-9370.notmuch/ [4] Mail from Andrii about not supporting old Clang in selftests: https://lore.kernel.org/bpf/CAEf4BzYBddPaEzRUs=jaWSo5kbf=LZdb7geAUVj85GxLQztuAQ@xxxxxxxxxxxxxx/ Brendan Jackman (11): bpf: x86: Factor out emission of ModR/M for *(reg + off) bpf: x86: Factor out emission of REX byte bpf: x86: Factor out a lookup table for some ALU opcodes bpf: Rename BPF_XADD and prepare to encode other atomics in .imm bpf: Move BPF_STX reserved field check into BPF_STX verifier code bpf: Add BPF_FETCH field / create atomic_fetch_add instruction bpf: Add instructions for atomic_[cmp]xchg bpf: Pull out a macro for interpreting atomic ALU operations bpf: Add bitwise atomic instructions bpf: Add tests for new BPF atomic operations bpf: Document new atomic instructions Documentation/networking/filter.rst | 56 +++- arch/arm/net/bpf_jit_32.c | 7 +- arch/arm64/net/bpf_jit_comp.c | 16 +- arch/mips/net/ebpf_jit.c | 11 +- arch/powerpc/net/bpf_jit_comp64.c | 25 +- arch/riscv/net/bpf_jit_comp32.c | 20 +- arch/riscv/net/bpf_jit_comp64.c | 16 +- arch/s390/net/bpf_jit_comp.c | 27 +- arch/sparc/net/bpf_jit_comp_64.c | 17 +- arch/x86/net/bpf_jit_comp.c | 217 ++++++++++----- arch/x86/net/bpf_jit_comp32.c | 6 +- drivers/net/ethernet/netronome/nfp/bpf/jit.c | 14 +- drivers/net/ethernet/netronome/nfp/bpf/main.h | 4 +- .../net/ethernet/netronome/nfp/bpf/verifier.c | 15 +- include/linux/filter.h | 25 +- include/uapi/linux/bpf.h | 10 +- kernel/bpf/core.c | 67 ++++- kernel/bpf/disasm.c | 43 ++- kernel/bpf/verifier.c | 75 ++++-- lib/test_bpf.c | 14 +- samples/bpf/bpf_insn.h | 4 +- samples/bpf/cookie_uid_helper_example.c | 8 +- samples/bpf/sock_example.c | 2 +- samples/bpf/test_cgrp2_attach.c | 5 +- tools/include/linux/filter.h | 24 +- tools/include/uapi/linux/bpf.h | 10 +- tools/testing/selftests/bpf/Makefile | 2 + .../selftests/bpf/prog_tests/atomics.c | 246 ++++++++++++++++++ .../bpf/prog_tests/cgroup_attach_multi.c | 4 +- tools/testing/selftests/bpf/progs/atomics.c | 154 +++++++++++ .../selftests/bpf/test_cgroup_storage.c | 2 +- .../selftests/bpf/verifier/atomic_and.c | 77 ++++++ .../selftests/bpf/verifier/atomic_cmpxchg.c | 96 +++++++ .../selftests/bpf/verifier/atomic_fetch_add.c | 106 ++++++++ .../selftests/bpf/verifier/atomic_or.c | 77 ++++++ .../selftests/bpf/verifier/atomic_xchg.c | 46 ++++ .../selftests/bpf/verifier/atomic_xor.c | 77 ++++++ tools/testing/selftests/bpf/verifier/ctx.c | 7 +- .../bpf/verifier/direct_packet_access.c | 4 +- .../testing/selftests/bpf/verifier/leak_ptr.c | 10 +- .../selftests/bpf/verifier/meta_access.c | 4 +- tools/testing/selftests/bpf/verifier/unpriv.c | 3 +- .../bpf/verifier/value_illegal_alu.c | 2 +- tools/testing/selftests/bpf/verifier/xadd.c | 18 +- 44 files changed, 1461 insertions(+), 212 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/atomics.c create mode 100644 tools/testing/selftests/bpf/progs/atomics.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_and.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_cmpxchg.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_fetch_add.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_or.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xchg.c create mode 100644 tools/testing/selftests/bpf/verifier/atomic_xor.c base-commit: 0e12c0271887f1b00b79b7612c1d4f0d3d34e8a8 -- 2.29.2.684.gfbc64c5ab5-goog
