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Date: Wed, 3 Jul 2019 14:39:44 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Andrii Nakryiko <andriin@...com>, andrii.nakryiko@...il.com,
bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
kernel-team@...com, yhs@...com
Subject: Re: [PATCH v5 bpf-next 4/9] libbpf: add kprobe/uprobe attach API
On 07/02/2019 01:58 AM, Andrii Nakryiko wrote:
> Add ability to attach to kernel and user probes and retprobes.
> Implementation depends on perf event support for kprobes/uprobes.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> Reviewed-by: Stanislav Fomichev <sdf@...gle.com>
> ---
> tools/lib/bpf/libbpf.c | 169 +++++++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 7 ++
> tools/lib/bpf/libbpf.map | 2 +
> 3 files changed, 178 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index bcaa294f819d..7b6142408b15 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4021,6 +4021,175 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog,
> return (struct bpf_link *)link;
> }
>
> +/*
> + * this function is expected to parse integer in the range of [0, 2^31-1] from
> + * given file using scanf format string fmt. If actual parsed value is
> + * negative, the result might be indistinguishable from error
> + */
> +static int parse_uint_from_file(const char *file, const char *fmt)
> +{
> + char buf[STRERR_BUFSIZE];
> + int err, ret;
> + FILE *f;
> +
> + f = fopen(file, "r");
> + if (!f) {
> + err = -errno;
> + pr_debug("failed to open '%s': %s\n", file,
> + libbpf_strerror_r(err, buf, sizeof(buf)));
> + return err;
> + }
> + err = fscanf(f, fmt, &ret);
> + if (err != 1) {
> + err = err == EOF ? -EIO : -errno;
> + pr_debug("failed to parse '%s': %s\n", file,
> + libbpf_strerror_r(err, buf, sizeof(buf)));
> + fclose(f);
> + return err;
> + }
> + fclose(f);
> + return ret;
> +}
> +
> +static int determine_kprobe_perf_type(void)
> +{
> + const char *file = "/sys/bus/event_source/devices/kprobe/type";
> +
> + return parse_uint_from_file(file, "%d\n");
> +}
> +
> +static int determine_uprobe_perf_type(void)
> +{
> + const char *file = "/sys/bus/event_source/devices/uprobe/type";
> +
> + return parse_uint_from_file(file, "%d\n");
> +}
> +
> +static int determine_kprobe_retprobe_bit(void)
> +{
> + const char *file = "/sys/bus/event_source/devices/kprobe/format/retprobe";
> +
> + return parse_uint_from_file(file, "config:%d\n");
> +}
> +
> +static int determine_uprobe_retprobe_bit(void)
> +{
> + const char *file = "/sys/bus/event_source/devices/uprobe/format/retprobe";
> +
> + return parse_uint_from_file(file, "config:%d\n");
> +}
> +
> +static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
> + uint64_t offset, int pid)
> +{
> + struct perf_event_attr attr = {};
> + char errmsg[STRERR_BUFSIZE];
> + int type, pfd, err;
> +
> + type = uprobe ? determine_uprobe_perf_type()
> + : determine_kprobe_perf_type();
> + if (type < 0) {
> + pr_warning("failed to determine %s perf type: %s\n",
> + uprobe ? "uprobe" : "kprobe",
> + libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
> + return type;
> + }
> + if (retprobe) {
> + int bit = uprobe ? determine_uprobe_retprobe_bit()
> + : determine_kprobe_retprobe_bit();
> +
> + if (bit < 0) {
> + pr_warning("failed to determine %s retprobe bit: %s\n",
> + uprobe ? "uprobe" : "kprobe",
> + libbpf_strerror_r(bit, errmsg,
> + sizeof(errmsg)));
> + return bit;
> + }
> + attr.config |= 1 << bit;
> + }
> + attr.size = sizeof(attr);
> + attr.type = type;
> + attr.config1 = (uint64_t)(void *)name; /* kprobe_func or uprobe_path */
> + attr.config2 = offset; /* kprobe_addr or probe_offset */
> +
> + /* pid filter is meaningful only for uprobes */
> + pfd = syscall(__NR_perf_event_open, &attr,
> + pid < 0 ? -1 : pid /* pid */,
> + pid == -1 ? 0 : -1 /* cpu */,
> + -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
> + if (pfd < 0) {
> + err = -errno;
> + pr_warning("%s perf_event_open() failed: %s\n",
> + uprobe ? "uprobe" : "kprobe",
> + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> + return err;
> + }
> + return pfd;
> +}
> +
> +struct bpf_link *bpf_program__attach_kprobe(struct bpf_program *prog,
> + bool retprobe,
> + const char *func_name)
> +{
> + char errmsg[STRERR_BUFSIZE];
> + struct bpf_link *link;
> + int pfd, err;
> +
> + pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
> + 0 /* offset */, -1 /* pid */);
> + if (pfd < 0) {
> + pr_warning("program '%s': failed to create %s '%s' perf event: %s\n",
> + bpf_program__title(prog, false),
> + retprobe ? "kretprobe" : "kprobe", func_name,
> + libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
> + return ERR_PTR(pfd);
> + }
> + link = bpf_program__attach_perf_event(prog, pfd);
> + if (IS_ERR(link)) {
> + close(pfd);
> + err = PTR_ERR(link);
> + pr_warning("program '%s': failed to attach to %s '%s': %s\n",
> + bpf_program__title(prog, false),
> + retprobe ? "kretprobe" : "kprobe", func_name,
> + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> + return link;
> + }
> + return link;
> +}
> +
> +struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,
> + bool retprobe, pid_t pid,
> + const char *binary_path,
> + size_t func_offset)
> +{
> + char errmsg[STRERR_BUFSIZE];
> + struct bpf_link *link;
> + int pfd, err;
> +
> + pfd = perf_event_open_probe(true /* uprobe */, retprobe,
> + binary_path, func_offset, pid);
> + if (pfd < 0) {
> + pr_warning("program '%s': failed to create %s '%s:0x%zx' perf event: %s\n",
> + bpf_program__title(prog, false),
> + retprobe ? "uretprobe" : "uprobe",
> + binary_path, func_offset,
> + libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
> + return ERR_PTR(pfd);
> + }
> + link = bpf_program__attach_perf_event(prog, pfd);
> + if (IS_ERR(link)) {
> + close(pfd);
> + err = PTR_ERR(link);
> + pr_warning("program '%s': failed to attach to %s '%s:0x%zx': %s\n",
> + bpf_program__title(prog, false),
> + retprobe ? "uretprobe" : "uprobe",
> + binary_path, func_offset,
> + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> + return link;
> + }
> + return link;
> +}
Hm, this only addresses half the feedback I had in prior version [0]. Patch 2/9
with bpf_link with destructor looks good to me, but my feedback from back then was
that all the kprobe/uprobe/tracepoint/raw_tracepoint should be split API-wise, so
you'll end up with something like the below, that is, 1) a set of functions that
only /create/ the bpf_link handle /once/, and 2) a helper that allows /attaching/
progs to one or multiple bpf_links. The set of APIs would look like:
struct bpf_link *bpf_link__create_kprobe(bool retprobe, const char *func_name);
struct bpf_link *bpf_link__create_uprobe(bool retprobe, pid_t pid,
const char *binary_path,
size_t func_offset);
int bpf_program__attach_to_link(struct bpf_link *link, struct bpf_program *prog);
int bpf_link__destroy(struct bpf_link *link);
This seems much more natural to me. Right now you sort of do both in one single API.
Detangling the bpf_program__attach_{uprobe,kprobe}() would also avoid that you have
to redo all the perf_event_open_probe() work over and over in order to get the pfd
context where you can later attach something to. Given bpf_program__attach_to_link()
API, you also wouldn't need to expose the bpf_program__attach_perf_event() from
patch 3/9. Thoughts?
[0] https://lore.kernel.org/bpf/a7780057-1d70-9ace-960b-ff65867dc277@iogearbox.net/
> enum bpf_perf_event_ret
> bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
> void **copy_mem, size_t *copy_size,
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 1bf66c4a9330..bd767cc11967 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -171,6 +171,13 @@ LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
>
> LIBBPF_API struct bpf_link *
> bpf_program__attach_perf_event(struct bpf_program *prog, int pfd);
> +LIBBPF_API struct bpf_link *
> +bpf_program__attach_kprobe(struct bpf_program *prog, bool retprobe,
> + const char *func_name);
> +LIBBPF_API struct bpf_link *
> +bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
> + pid_t pid, const char *binary_path,
> + size_t func_offset);
>
> struct bpf_insn;
>
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 756f5aa802e9..57a40fb60718 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -169,7 +169,9 @@ LIBBPF_0.0.4 {
> global:
> bpf_link__destroy;
> bpf_object__load_xattr;
> + bpf_program__attach_kprobe;
> bpf_program__attach_perf_event;
> + bpf_program__attach_uprobe;
> btf_dump__dump_type;
> btf_dump__free;
> btf_dump__new;
>
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