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Daniel Borkmann says:
====================
pull-request: bpf-next 2022-03-04
We've added 32 non-merge commits during the last 14 day(s) which contain
a total of 59 files changed, 1038 insertions(+), 473 deletions(-).
The main changes are:
1) Optimize BPF stackmap's build_id retrieval by caching last valid build_id,
as consecutive stack frames are likely to be in the same VMA and therefore
have the same build id, from Hao Luo.
2) Several improvements to arm64 BPF JIT, that is, support for JITing
the atomic[64]_fetch_add, atomic[64]_[fetch_]{and,or,xor} and lastly
atomic[64]_{xchg|cmpxchg}. Also fix the BTF line info dump for JITed
programs, from Hou Tao.
3) Optimize generic BPF map batch deletion by only enforcing synchronize_rcu()
barrier once upon return to user space, from Eric Dumazet.
4) For kernel build parse DWARF and generate BTF through pahole with enabled
multithreading, from Kui-Feng Lee.
5) BPF verifier usability improvements by making log info more concise and
replacing inv with scalar type name, from Mykola Lysenko.
6) Two follow-up fixes for BPF prog JIT pack allocator, from Song Liu.
7) Add a new Kconfig to allow for loading kernel modules with non-matching
BTF type info; their BTF info is then removed on load, from Connor O'Brien.
8) Remove reallocarray() usage from bpftool and switch to libbpf_reallocarray()
in order to fix compilation errors for older glibc, from Mauricio Vásquez.
9) Fix libbpf to error on conflicting name in BTF when type declaration
appears before the definition, from Xu Kuohai.
10) Fix issue in BPF preload for in-kernel light skeleton where loaded BPF
program fds prevent init process from setting up fd 0-2, from Yucong Sun.
11) Fix libbpf reuse of pinned perf RB map when max_entries is auto-determined
by libbpf, from Stijn Tintel.
12) Several cleanups for libbpf and a fix to enforce perf RB map #pages to be
non-zero, from Yuntao Wang.
* https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (32 commits)
bpf: Small BPF verifier log improvements
libbpf: Add a check to ensure that page_cnt is non-zero
bpf, x86: Set header->size properly before freeing it
x86: Disable HAVE_ARCH_HUGE_VMALLOC on 32-bit x86
bpf, test_run: Fix overflow in XDP frags bpf_test_finish
selftests/bpf: Update btf_dump case for conflicting names
libbpf: Skip forward declaration when counting duplicated type names
bpf: Add some description about BPF_JIT_ALWAYS_ON in Kconfig
bpf, docs: Add a missing colon in verifier.rst
bpf: Cache the last valid build_id
libbpf: Fix BPF_MAP_TYPE_PERF_EVENT_ARRAY auto-pinning
bpf, selftests: Use raw_tp program for atomic test
bpf, arm64: Support more atomic operations
bpftool: Remove redundant slashes
bpf: Add config to allow loading modules with BTF mismatches
bpf, arm64: Feed byte-offset into bpf line info
bpf, arm64: Call build_prologue() first in first JIT pass
bpf: Fix issue with bpf preload module taking over stdout/stdin of kernel.
bpftool: Bpf skeletons assert type sizes
bpf: Cleanup comments
...
====================
Link: https://lore.kernel.org/r/20220304164313.31675-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
==================
BPF Selftest Notes
==================
General instructions on running selftests can be found in
`Documentation/bpf/bpf_devel_QA.rst`__.
__ /Documentation/bpf/bpf_devel_QA.rst#q-how-to-run-bpf-selftests
=========================
Running Selftests in a VM
=========================
It's now possible to run the selftests using ``tools/testing/selftests/bpf/vmtest.sh``.
The script tries to ensure that the tests are run with the same environment as they
would be run post-submit in the CI used by the Maintainers.
This script downloads a suitable Kconfig and VM userspace image from the system used by
the CI. It builds the kernel (without overwriting your existing Kconfig), recompiles the
bpf selftests, runs them (by default ``tools/testing/selftests/bpf/test_progs``) and
saves the resulting output (by default in ``~/.bpf_selftests``).
Script dependencies:
- clang (preferably built from sources, https://github.com/llvm/llvm-project);
- pahole (preferably built from sources, https://git.kernel.org/pub/scm/devel/pahole/pahole.git/);
- qemu;
- docutils (for ``rst2man``);
- libcap-devel.
For more information on about using the script, run:
.. code-block:: console
$ tools/testing/selftests/bpf/vmtest.sh -h
.. note:: The script uses pahole and clang based on host environment setting.
If you want to change pahole and llvm, you can change `PATH` environment
variable in the beginning of script.
.. note:: The script currently only supports x86_64.
Additional information about selftest failures are
documented here.
profiler[23] test failures with clang/llvm <12.0.0
==================================================
With clang/llvm <12.0.0, the profiler[23] test may fail.
The symptom looks like
.. code-block:: c
// r9 is a pointer to map_value
// r7 is a scalar
17: bf 96 00 00 00 00 00 00 r6 = r9
18: 0f 76 00 00 00 00 00 00 r6 += r7
math between map_value pointer and register with unbounded min value is not allowed
// the instructions below will not be seen in the verifier log
19: a5 07 01 00 01 01 00 00 if r7 < 257 goto +1
20: bf 96 00 00 00 00 00 00 r6 = r9
// r6 is used here
The verifier will reject such code with above error.
At insn 18 the r7 is indeed unbounded. The later insn 19 checks the bounds and
the insn 20 undoes map_value addition. It is currently impossible for the
verifier to understand such speculative pointer arithmetic.
Hence `this patch`__ addresses it on the compiler side. It was committed on llvm 12.
__ https://reviews.llvm.org/D85570
The corresponding C code
.. code-block:: c
for (int i = 0; i < MAX_CGROUPS_PATH_DEPTH; i++) {
filepart_length = bpf_probe_read_str(payload, ...);
if (filepart_length <= MAX_PATH) {
barrier_var(filepart_length); // workaround
payload += filepart_length;
}
}
bpf_iter test failures with clang/llvm 10.0.0
=============================================
With clang/llvm 10.0.0, the following two bpf_iter tests failed:
* ``bpf_iter/ipv6_route``
* ``bpf_iter/netlink``
The symptom for ``bpf_iter/ipv6_route`` looks like
.. code-block:: c
2: (79) r8 = *(u64 *)(r1 +8)
...
14: (bf) r2 = r8
15: (0f) r2 += r1
; BPF_SEQ_PRINTF(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
16: (7b) *(u64 *)(r8 +64) = r2
only read is supported
The symptom for ``bpf_iter/netlink`` looks like
.. code-block:: c
; struct netlink_sock *nlk = ctx->sk;
2: (79) r7 = *(u64 *)(r1 +8)
...
15: (bf) r2 = r7
16: (0f) r2 += r1
; BPF_SEQ_PRINTF(seq, "%pK %-3d ", s, s->sk_protocol);
17: (7b) *(u64 *)(r7 +0) = r2
only read is supported
This is due to a llvm BPF backend bug. `The fix`__
has been pushed to llvm 10.x release branch and will be
available in 10.0.1. The patch is available in llvm 11.0.0 trunk.
__ https://reviews.llvm.org/D78466
bpf_verif_scale/loop6.o test failure with Clang 12
==================================================
With Clang 12, the following bpf_verif_scale test failed:
* ``bpf_verif_scale/loop6.o``
The verifier output looks like
.. code-block:: c
R1 type=ctx expected=fp
The sequence of 8193 jumps is too complex.
The reason is compiler generating the following code
.. code-block:: c
; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
14: 16 05 40 00 00 00 00 00 if w5 == 0 goto +64 <LBB0_6>
15: bc 51 00 00 00 00 00 00 w1 = w5
16: 04 01 00 00 ff ff ff ff w1 += -1
17: 67 05 00 00 20 00 00 00 r5 <<= 32
18: 77 05 00 00 20 00 00 00 r5 >>= 32
19: a6 01 01 00 05 00 00 00 if w1 < 5 goto +1 <LBB0_4>
20: b7 05 00 00 06 00 00 00 r5 = 6
00000000000000a8 <LBB0_4>:
21: b7 02 00 00 00 00 00 00 r2 = 0
22: b7 01 00 00 00 00 00 00 r1 = 0
; for (i = 0; (i < VIRTIO_MAX_SGS) && (i < num); i++) {
23: 7b 1a e0 ff 00 00 00 00 *(u64 *)(r10 - 32) = r1
24: 7b 5a c0 ff 00 00 00 00 *(u64 *)(r10 - 64) = r5
Note that insn #15 has w1 = w5 and w1 is refined later but
r5(w5) is eventually saved on stack at insn #24 for later use.
This cause later verifier failure. The bug has been `fixed`__ in
Clang 13.
__ https://reviews.llvm.org/D97479
BPF CO-RE-based tests and Clang version
=======================================
A set of selftests use BPF target-specific built-ins, which might require
bleeding-edge Clang versions (Clang 12 nightly at this time).
Few sub-tests of core_reloc test suit (part of test_progs test runner) require
the following built-ins, listed with corresponding Clang diffs introducing
them to Clang/LLVM. These sub-tests are going to be skipped if Clang is too
old to support them, they shouldn't cause build failures or runtime test
failures:
- __builtin_btf_type_id() [0_, 1_, 2_];
- __builtin_preserve_type_info(), __builtin_preserve_enum_value() [3_, 4_].
.. _0: https://reviews.llvm.org/D74572
.. _1: https://reviews.llvm.org/D74668
.. _2: https://reviews.llvm.org/D85174
.. _3: https://reviews.llvm.org/D83878
.. _4: https://reviews.llvm.org/D83242
Floating-point tests and Clang version
======================================
Certain selftests, e.g. core_reloc, require support for the floating-point
types, which was introduced in `Clang 13`__. The older Clang versions will
either crash when compiling these tests, or generate an incorrect BTF.
__ https://reviews.llvm.org/D83289
Kernel function call test and Clang version
===========================================
Some selftests (e.g. kfunc_call and bpf_tcp_ca) require a LLVM support
to generate extern function in BTF. It was introduced in `Clang 13`__.
Without it, the error from compiling bpf selftests looks like:
.. code-block:: console
libbpf: failed to find BTF for extern 'tcp_slow_start' [25] section: -2
__ https://reviews.llvm.org/D93563
btf_tag test and Clang version
==============================
The btf_tag selftest requires LLVM support to recognize the btf_decl_tag and
btf_type_tag attributes. They are introduced in `Clang 14` [0_, 1_].
The subtests ``btf_type_tag_user_{mod1, mod2, vmlinux}`` also requires
pahole version ``1.23``.
Without them, the btf_tag selftest will be skipped and you will observe:
.. code-block:: console
#<test_num> btf_tag:SKIP
.. _0: https://reviews.llvm.org/D111588
.. _1: https://reviews.llvm.org/D111199
Clang dependencies for static linking tests
===========================================
linked_vars, linked_maps, and linked_funcs tests depend on `Clang fix`__ to
generate valid BTF information for weak variables. Please make sure you use
Clang that contains the fix.
__ https://reviews.llvm.org/D100362
Clang relocation changes
========================
Clang 13 patch `clang reloc patch`_ made some changes on relocations such
that existing relocation types are broken into more types and
each new type corresponds to only one way to resolve relocation.
See `kernel llvm reloc`_ for more explanation and some examples.
Using clang 13 to compile old libbpf which has static linker support,
there will be a compilation failure::
libbpf: ELF relo #0 in section #6 has unexpected type 2 in .../bpf_tcp_nogpl.o
Here, ``type 2`` refers to new relocation type ``R_BPF_64_ABS64``.
To fix this issue, user newer libbpf.
.. Links
.. _clang reloc patch: https://reviews.llvm.org/D102712
.. _kernel llvm reloc: /Documentation/bpf/llvm_reloc.rst
Clang dependencies for the u32 spill test (xdpwall)
===================================================
The xdpwall selftest requires a change in `Clang 14`__.
Without it, the xdpwall selftest will fail and the error message
from running test_progs will look like:
.. code-block:: console
test_xdpwall:FAIL:Does LLVM have https://reviews.llvm.org/D109073? unexpected error: -4007
__ https://reviews.llvm.org/D109073