Recently Luiz Capitulino reported BPF test failure for kernel version
6.1.36 (see [7]). The following test_verifier test failed:
"precise: ST insn causing spi > allocated_stack".
After back-port of the following upstream commit:
ecdf985d7615 ("bpf: track immediate values written to stack by BPF_ST instruction")
Investigation in [8] shows that test failure is not a bug, but a
difference in BPF verifier behavior between upstream, where commits
[1,2,3] by Andrii Nakryiko are present, and 6.1.36, where these
commits are absent. Both Luiz and Greg suggested back-porting [1,2,3]
from upstream to avoid divergences.
Commits [1,2,3] break test_progs selftest "align/packet variable offset",
commit [4] fixes this selftest.
I did some additional testing using the following compiler versions:
- Kernel compilation
- gcc version 11.3.0
- BPF tests compilation
- clang version 16.0.6
- clang version 17.0.0 (fa46feb31481)
And identified a few more failing BPF selftests:
- Tests failing with LLVM 16:
- test_verifier:
- precise: ST insn causing spi > allocated_stack FAIL (fixed by [1,2,3])
- test_progs:
- sk_assign (fixed by [6])
- Tests failing with LLVM 17:
- test_verifier:
- precise: ST insn causing spi > allocated_stack FAIL (fixed by [1,2,3])
- test_progs:
- fexit_bpf2bpf/func_replace_verify (fixed by [5])
- fexit_bpf2bpf/func_replace_return_code (fixed by [5])
- sk_assign (fixed by [6])
Commits [4,5,6] only apply to BPF selftests and don't change verifier
behavior.
After applying all of the listed commits I have test_verifier,
test_progs, test_progs-no_alu32 and test_maps passing on my x86 setup,
both for LLVM 16 and LLVM 17.
Upstream commits in chronological order:
[1] be2ef8161572 ("bpf: allow precision tracking for programs with subprogs")
[2] f63181b6ae79 ("bpf: stop setting precise in current state")
[3] 7a830b53c17b ("bpf: aggressively forget precise markings during state checkpointing")
[4] 4f999b767769 ("selftests/bpf: make test_align selftest more robust")
[5] 63d78b7e8ca2 ("selftests/bpf: Workaround verification failure for fexit_bpf2bpf/func_replace_return_code")
[6] 7ce878ca81bc ("selftests/bpf: Fix sk_assign on s390x")
Links:
[7] https://lore.kernel.org/stable/935c4751-d368-df29-33a6-9f4fcae720fa@xxxxxxxxxx/
[8] https://lore.kernel.org/stable/c9b10a8a551edafdfec855fbd35757c6238ad258.camel@xxxxxxxxx/
Reported-by: Luiz Capitulino <luizcap@xxxxxxxxxx>
Andrii Nakryiko (4):
bpf: allow precision tracking for programs with subprogs
bpf: stop setting precise in current state
bpf: aggressively forget precise markings during state checkpointing
selftests/bpf: make test_align selftest more robust
Ilya Leoshkevich (1):
selftests/bpf: Fix sk_assign on s390x
Yonghong Song (1):
selftests/bpf: Workaround verification failure for
fexit_bpf2bpf/func_replace_return_code
kernel/bpf/verifier.c | 202 ++++++++++++++++--
.../testing/selftests/bpf/prog_tests/align.c | 38 ++--
.../selftests/bpf/prog_tests/sk_assign.c | 25 ++-
.../selftests/bpf/progs/connect4_prog.c | 2 +-
.../selftests/bpf/progs/test_sk_assign.c | 11 +
.../bpf/progs/test_sk_assign_libbpf.c | 3 +
6 files changed, 247 insertions(+), 34 deletions(-)
create mode 100644 tools/testing/selftests/bpf/progs/test_sk_assign_libbpf.c
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2.41.0
