On 3/18/25 7:33 AM, Anton Protopopov wrote:
This patchset implements new type of map, instruction set, and uses
it to build support for BPF static keys. The same map will be later
used to provide support for indirect jumps and indirect calls. See
[1], [2] for more context.
Short table of contents:
* patches 1, 9, 10, 11 are simple fixes (which can be sent
independently, if acked)
* patches 2, 3 add a new map type, BPF_MAP_TYPE_INSN_SET, and
corresponding selftests. This map is used to track how original
instructions were relocated into 'xlated' during the verification
* patches 4, 5, 6, 7, 8 add support for static keys (kernel only)
using (an extension) to that new map type. Only x86 support is
added in this RFC
* patches 12, 13, 14 add libbpf-side support for static keys and
selftests
It is RFC for a few reasons:
1) The kernel side of the static keys looks clear, however, the
libbpf side is not _that_ clear. I thought that this is better to
commit to a particular userspace design, as any particular design
requires a lot of changes on the libbpf side. See patch 12 for
the details
2) The libbpf part of the series requires a patched LLVM (see [3]),
which adds support for gotol_or_nop/nop_or_gotol instructions, so
selftests would not compile in CI.
3) Patch 4 adds support for a new BPF instruction. It looks
reasonable to use an extended BPF_JMP|BPF_JA instruction, and not
may_goto. Reasons: a follow up will add support for
BPF_JMP|BPF_JA|BPF_X (indirect jumps), which also utilizes INSN_SET maps (see [2]).
Then another follow up will add support CALL|BPF_X, for which there's
no corresponding magic instruction (to be discussed at the following
LSF/MM/BPF).
Besides these reasons, there are some questions / known bugs,
which will be fixed once the general plan is confirmed:
* bpf_jit_blind_constants will patch code, which is ignored in this
RFC series. The solution would be either moving tracking
instruction sets to bpf_prog from the verifier environment,
or moving bpf_jit_blind_constants upper the stack (right now,
this is the first thing which every jit does, so maybe it can
be actually executed from the verifier, and provide env context)
* gen-loader not supported, fd_array usage in libbpf should be
re-designed (see patch 12 for more details)
* insn_off -> insn_set map mapping should be optimized (now it is
brute force)
Links:
1. http://oldvger.kernel.org/bpfconf2024_material/bpf_static_keys.pdf
2. https://lpc.events/event/18/contributions/1941/
3. https://github.com/aspsk/llvm-project/tree/static-keys
For llvm patch in [3], please remove changes in function isValidIdInMiddle()
as gotol_or_nop or nop_or_gotol will not appear in the *middle* of any
instruction. "gotol" should not be there either, I may remove it sometime
later.
Anton Protopopov (14):
bpf: fix a comment describing bpf_attr
bpf: add new map type: instructions set
selftests/bpf: add selftests for new insn_set map
bpf: add support for an extended JA instruction
bpf: Add kernel/bpftool asm support for new instructions
bpf: add BPF_STATIC_KEY_UPDATE syscall
bpf: save the start of functions in bpf_prog_aux
bpf, x86: implement static key support
selftests/bpf: add guard macros around likely/unlikely
libbpf: add likely/unlikely macros
selftests/bpf: remove likely/unlikely definitions
libbpf: BPF Static Keys support
libbpf: Add bpf_static_key_update() API
selftests/bpf: Add tests for BPF static calls
arch/x86/net/bpf_jit_comp.c | 65 +-
include/linux/bpf.h | 28 +
include/linux/bpf_types.h | 1 +
include/linux/bpf_verifier.h | 2 +
include/uapi/linux/bpf.h | 40 +-
kernel/bpf/Makefile | 2 +-
kernel/bpf/bpf_insn_set.c | 400 +++++++++++
kernel/bpf/core.c | 5 +
kernel/bpf/disasm.c | 33 +-
kernel/bpf/syscall.c | 28 +
kernel/bpf/verifier.c | 94 ++-
tools/include/uapi/linux/bpf.h | 40 +-
tools/lib/bpf/bpf.c | 17 +
tools/lib/bpf/bpf.h | 19 +
tools/lib/bpf/bpf_helpers.h | 63 ++
tools/lib/bpf/libbpf.c | 362 +++++++++-
tools/lib/bpf/libbpf.map | 1 +
tools/lib/bpf/libbpf_internal.h | 3 +
tools/lib/bpf/linker.c | 6 +-
.../selftests/bpf/bpf_arena_spin_lock.h | 3 -
.../selftests/bpf/prog_tests/bpf_insn_set.c | 639 ++++++++++++++++++
.../bpf/prog_tests/bpf_static_keys.c | 359 ++++++++++
.../selftests/bpf/progs/bpf_static_keys.c | 131 ++++
tools/testing/selftests/bpf/progs/iters.c | 2 -
24 files changed, 2315 insertions(+), 28 deletions(-)
create mode 100644 kernel/bpf/bpf_insn_set.c
create mode 100644 tools/testing/selftests/bpf/prog_tests/bpf_insn_set.c
create mode 100644 tools/testing/selftests/bpf/prog_tests/bpf_static_keys.c
create mode 100644 tools/testing/selftests/bpf/progs/bpf_static_keys.c
