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SubjectRe: [PATCH bpf-next 1/2] libbpf: Add probe for large INSN limit
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On 12/27/19 12:06 PM, Michal Rostecki wrote:
> Introduce a new probe which checks whether kernel has large maximum
> program size (1M) which was increased in commit c04c0d2b968a ("bpf:
> increase complexity limit and maximum program size").
>
> Based on the similar check in Cilium[0], authored by Daniel Borkmann.
>
> [0] https://github.com/cilium/cilium/commit/657d0f585afd26232cfa5d4e70b6f64d2ea91596
>
> Co-authored-by: Daniel Borkmann <daniel@iogearbox.net>
> Signed-off-by: Michal Rostecki <mrostecki@suse.de>
> ---
> tools/lib/bpf/libbpf.h | 1 +
> tools/lib/bpf/libbpf.map | 1 +
> tools/lib/bpf/libbpf_probes.c | 23 +++++++++++++++++++++++
> 3 files changed, 25 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index fe592ef48f1b..26bf539f1b3c 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -521,6 +521,7 @@ LIBBPF_API bool bpf_probe_prog_type(enum bpf_prog_type prog_type,
> LIBBPF_API bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex);
> LIBBPF_API bool bpf_probe_helper(enum bpf_func_id id,
> enum bpf_prog_type prog_type, __u32 ifindex);
> +LIBBPF_API bool bpf_probe_large_insn_limit(__u32 ifindex);
>
> /*
> * Get bpf_prog_info in continuous memory
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index e9713a574243..b300d74c921a 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -219,6 +219,7 @@ LIBBPF_0.0.7 {
> bpf_object__detach_skeleton;
> bpf_object__load_skeleton;
> bpf_object__open_skeleton;
> + bpf_probe_large_insn_limit;
> bpf_prog_attach_xattr;
> bpf_program__attach;
> bpf_program__name;
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index a9eb8b322671..925f95106a52 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -17,6 +17,8 @@
> #include "libbpf.h"
> #include "libbpf_internal.h"
>
> +#define INSN_REPEAT 4128
> +
> static bool grep(const char *buffer, const char *pattern)
> {
> return !!strstr(buffer, pattern);
> @@ -321,3 +323,24 @@ bool bpf_probe_helper(enum bpf_func_id id, enum bpf_prog_type prog_type,
>
> return res;
> }
> +
> +/*
> + * Probe for availability of kernel commit (5.3):
> + *
> + * c04c0d2b968a ("bpf: increase complexity limit and maximum program size")
> + */
> +bool bpf_probe_large_insn_limit(__u32 ifindex)
> +{
> + struct bpf_insn insns[INSN_REPEAT + 1];
> + int i;

Looks good, but lets test for 'BPF_MAXINSNS + 1' number of total insns, less
arbitrary than 4128.

> + for (i = 0; i < INSN_REPEAT; i++)
> + insns[i] = BPF_MOV64_IMM(BPF_REG_0, 1);
> + insns[INSN_REPEAT] = BPF_EXIT_INSN();
> +
> + errno = 0;
> + probe_load(BPF_PROG_TYPE_SCHED_CLS, insns, ARRAY_SIZE(insns), NULL, 0,
> + ifindex);
> +
> + return errno != E2BIG && errno != EINVAL;
> +}
>

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