From 668ace0ea5ab5acdb33cff0b66fcd8f41c16a0b0 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Sun, 15 Aug 2021 00:06:02 -0700 Subject: [PATCH] libbpf: Use BPF perf link when supported by kernel Detect kernel support for BPF perf link and prefer it when attaching to perf_event, tracepoint, kprobe/uprobe. Underlying perf_event FD will be kept open until BPF link is destroyed, at which point both perf_event FD and BPF link FD will be closed. This preserves current behavior in which perf_event FD is open for the duration of bpf_link's lifetime and user is able to "disconnect" bpf_link from underlying FD (with bpf_link__disconnect()), so that bpf_link__destroy() doesn't close underlying perf_event FD.When BPF perf link is used, disconnect will keep both perf_event and bpf_link FDs open, so it will be up to (advanced) user to close them. This approach is demonstrated in bpf_cookie.c selftests, added in this patch set. Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20210815070609.987780-10-andrii@kernel.org --- tools/lib/bpf/libbpf.c | 111 +++++++++++++++++++++++++++++++++-------- 1 file changed, 90 insertions(+), 21 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index d30e3282bfc7..5dc15f5b4b78 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -193,6 +193,8 @@ enum kern_feature_id { FEAT_MODULE_BTF, /* BTF_KIND_FLOAT support */ FEAT_BTF_FLOAT, + /* BPF perf link support */ + FEAT_PERF_LINK, __FEAT_CNT, }; @@ -4337,6 +4339,37 @@ static int probe_module_btf(void) return !err; } +static int probe_perf_link(void) +{ + struct bpf_load_program_attr attr; + struct bpf_insn insns[] = { + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }; + int prog_fd, link_fd, err; + + memset(&attr, 0, sizeof(attr)); + attr.prog_type = BPF_PROG_TYPE_TRACEPOINT; + attr.insns = insns; + attr.insns_cnt = ARRAY_SIZE(insns); + attr.license = "GPL"; + prog_fd = bpf_load_program_xattr(&attr, NULL, 0); + if (prog_fd < 0) + return -errno; + + /* use invalid perf_event FD to get EBADF, if link is supported; + * otherwise EINVAL should be returned + */ + link_fd = bpf_link_create(prog_fd, -1, BPF_PERF_EVENT, NULL); + err = -errno; /* close() can clobber errno */ + + if (link_fd >= 0) + close(link_fd); + close(prog_fd); + + return link_fd < 0 && err == -EBADF; +} + enum kern_feature_result { FEAT_UNKNOWN = 0, FEAT_SUPPORTED = 1, @@ -4387,6 +4420,9 @@ static struct kern_feature_desc { [FEAT_BTF_FLOAT] = { "BTF_KIND_FLOAT support", probe_kern_btf_float, }, + [FEAT_PERF_LINK] = { + "BPF perf link support", probe_perf_link, + }, }; static bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id) @@ -8951,23 +8987,38 @@ int bpf_link__unpin(struct bpf_link *link) return 0; } -static int bpf_link__detach_perf_event(struct bpf_link *link) +struct bpf_link_perf { + struct bpf_link link; + int perf_event_fd; +}; + +static int bpf_link_perf_detach(struct bpf_link *link) { - int err; + struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link); + int err = 0; - err = ioctl(link->fd, PERF_EVENT_IOC_DISABLE, 0); - if (err) + if (ioctl(perf_link->perf_event_fd, PERF_EVENT_IOC_DISABLE, 0) < 0) err = -errno; + if (perf_link->perf_event_fd != link->fd) + close(perf_link->perf_event_fd); close(link->fd); + return libbpf_err(err); } +static void bpf_link_perf_dealloc(struct bpf_link *link) +{ + struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link); + + free(perf_link); +} + struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, int pfd) { char errmsg[STRERR_BUFSIZE]; - struct bpf_link *link; - int prog_fd, err; + struct bpf_link_perf *link; + int prog_fd, link_fd = -1, err; if (pfd < 0) { pr_warn("prog '%s': invalid perf event FD %d\n", @@ -8984,27 +9035,45 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, int pf link = calloc(1, sizeof(*link)); if (!link) return libbpf_err_ptr(-ENOMEM); - link->detach = &bpf_link__detach_perf_event; - link->fd = pfd; + link->link.detach = &bpf_link_perf_detach; + link->link.dealloc = &bpf_link_perf_dealloc; + link->perf_event_fd = pfd; - if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, prog_fd) < 0) { - err = -errno; - free(link); - pr_warn("prog '%s': failed to attach to pfd %d: %s\n", - prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg))); - if (err == -EPROTO) - pr_warn("prog '%s': try add PERF_SAMPLE_CALLCHAIN to or remove exclude_callchain_[kernel|user] from pfd %d\n", - prog->name, pfd); - return libbpf_err_ptr(err); + if (kernel_supports(prog->obj, FEAT_PERF_LINK)) { + link_fd = bpf_link_create(prog_fd, pfd, BPF_PERF_EVENT, NULL); + if (link_fd < 0) { + err = -errno; + pr_warn("prog '%s': failed to create BPF link for perf_event FD %d: %d (%s)\n", + prog->name, pfd, + err, libbpf_strerror_r(err, errmsg, sizeof(errmsg))); + goto err_out; + } + link->link.fd = link_fd; + } else { + if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, prog_fd) < 0) { + err = -errno; + pr_warn("prog '%s': failed to attach to perf_event FD %d: %s\n", + prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg))); + if (err == -EPROTO) + pr_warn("prog '%s': try add PERF_SAMPLE_CALLCHAIN to or remove exclude_callchain_[kernel|user] from pfd %d\n", + prog->name, pfd); + goto err_out; + } + link->link.fd = pfd; } if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) { err = -errno; - free(link); - pr_warn("prog '%s': failed to enable pfd %d: %s\n", + pr_warn("prog '%s': failed to enable perf_event FD %d: %s\n", prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg))); - return libbpf_err_ptr(err); + goto err_out; } - return link; + + return &link->link; +err_out: + if (link_fd >= 0) + close(link_fd); + free(link); + return libbpf_err_ptr(err); } /* -- GitLab