We have a usecase where we want to audit symbol names (if available) in callback registration hooks. (ex: fentry/nf_register_net_hook) A few months back, I proposed a bpf_kallsyms_lookup series but it was decided in the reviews that a more generic helper, bpf_snprintf, would be more useful. This series implements the helper according to the feedback received in https://lore.kernel.org/bpf/20201126165748.1748417-1-revest@xxxxxxxxxx/T/#u - A new arg type guarantees the NULL-termination of string arguments and lets us pass format strings in only one arg - A new helper is implemented using that guarantee. Because the format string is known at verification time, the format string validation is done by the verifier - To implement a series of tests for bpf_snprintf, the logic for marshalling variadic args in a fixed-size array is reworked as per: https://lore.kernel.org/bpf/20210310015455.1095207-1-revest@xxxxxxxxxxxx/T/#u --- Changes in v3: - Simplified temporary buffer acquisition with try_get_fmt_tmp_buf() - Made zero-termination check more consistent - Allowed NULL output_buffer - Simplified the BPF_CAST_FMT_ARG macro - Three new test cases: number padding, simple string with no arg and string length extraction only with a NULL output buffer - Clarified helper's description for edge cases (eg: str_size == 0) - Lots of cosmetic changes --- Changes in v2: - Extracted the format validation/argument sanitization in a generic way for all printf-like helpers. - bpf_snprintf's str_size can now be 0 - bpf_snprintf is now exposed to all BPF program types - We now preempt_disable when using a per-cpu temporary buffer - Addressed a few cosmetic changes Florent Revest (6): bpf: Factorize bpf_trace_printk and bpf_seq_printf bpf: Add a ARG_PTR_TO_CONST_STR argument type bpf: Add a bpf_snprintf helper libbpf: Initialize the bpf_seq_printf parameters array field by field libbpf: Introduce a BPF_SNPRINTF helper macro selftests/bpf: Add a series of tests for bpf_snprintf include/linux/bpf.h | 7 + include/uapi/linux/bpf.h | 28 + kernel/bpf/helpers.c | 2 + kernel/bpf/verifier.c | 82 +++ kernel/trace/bpf_trace.c | 579 +++++++++--------- tools/include/uapi/linux/bpf.h | 28 + tools/lib/bpf/bpf_tracing.h | 58 +- .../selftests/bpf/prog_tests/snprintf.c | 81 +++ .../selftests/bpf/progs/test_snprintf.c | 74 +++ 9 files changed, 647 insertions(+), 292 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf.c create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf.c -- 2.31.1.295.g9ea45b61b8-goog
