From 8094029330a2f03fb406ecff80671cf27ce28d42 Mon Sep 17 00:00:00 2001 From: Chuang Wang Date: Wed, 29 Jun 2022 23:18:45 +0800 Subject: [PATCH 1/3] libbpf: Cleanup the legacy kprobe_event on failed add/attach_event() Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with livepatch"), in a scenario where livepatch and kprobe coexist on the same function entry, the creation of kprobe_event using add_kprobe_event_legacy() will be successful, at the same time as a trace event (e.g. /debugfs/tracing/events/kprobe/XXX) will exist, but perf_event_open() will return an error because both livepatch and kprobe use FTRACE_OPS_FL_IPMODIFY. As follows: 1) add a livepatch $ insmod livepatch-XXX.ko 2) add a kprobe using tracefs API (i.e. add_kprobe_event_legacy) $ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events 3) enable this kprobe (i.e. sys_perf_event_open) This will return an error, -EBUSY. On Andrii Nakryiko's comment, few error paths in bpf_program__attach_kprobe_opts() that should need to call remove_kprobe_event_legacy(). With this patch, whenever an error is returned after add_kprobe_event_legacy() or bpf_program__attach_perf_event_opts(), this ensures that the created kprobe_event is cleaned. Signed-off-by: Chuang Wang Signed-off-by: Jingren Zhou Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220629151848.65587-2-nashuiliang@gmail.com --- tools/lib/bpf/libbpf.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 64c4cc6140d3..8a441d304924 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -9877,10 +9877,11 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe, } type = determine_kprobe_perf_type_legacy(probe_name, retprobe); if (type < 0) { + err = type; pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n", kfunc_name, offset, - libbpf_strerror_r(type, errmsg, sizeof(errmsg))); - return type; + libbpf_strerror_r(err, errmsg, sizeof(errmsg))); + goto err_clean_legacy; } attr.size = sizeof(attr); attr.config = type; @@ -9894,9 +9895,14 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe, err = -errno; pr_warn("legacy kprobe perf_event_open() failed: %s\n", libbpf_strerror_r(err, errmsg, sizeof(errmsg))); - return err; + goto err_clean_legacy; } return pfd; + +err_clean_legacy: + /* Clear the newly added legacy kprobe_event */ + remove_kprobe_event_legacy(probe_name, retprobe); + return err; } struct bpf_link * @@ -9953,7 +9959,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, prog->name, retprobe ? "kretprobe" : "kprobe", func_name, offset, libbpf_strerror_r(err, errmsg, sizeof(errmsg))); - goto err_out; + goto err_clean_legacy; } if (legacy) { struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link); @@ -9964,6 +9970,10 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, } return link; + +err_clean_legacy: + if (legacy) + remove_kprobe_event_legacy(legacy_probe, retprobe); err_out: free(legacy_probe); return libbpf_err_ptr(err); From 5666fc997ccb93859ea1d4437936c64c6d75c060 Mon Sep 17 00:00:00 2001 From: Chuang Wang Date: Wed, 29 Jun 2022 23:18:46 +0800 Subject: [PATCH 2/3] libbpf: Fix wrong variable used in perf_event_uprobe_open_legacy() Use "type" as opposed to "err" in pr_warn() after determine_uprobe_perf_type_legacy() returns an error. Signed-off-by: Chuang Wang Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220629151848.65587-3-nashuiliang@gmail.com --- tools/lib/bpf/libbpf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 8a441d304924..571acd614dce 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -10249,7 +10249,7 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe, type = determine_uprobe_perf_type_legacy(probe_name, retprobe); if (type < 0) { pr_warn("failed to determine legacy uprobe event id for %s:0x%zx: %d\n", - binary_path, offset, err); + binary_path, offset, type); return type; } From 2655144fb49bae26eae038c6d056f824a7db2726 Mon Sep 17 00:00:00 2001 From: Chuang Wang Date: Wed, 29 Jun 2022 23:18:47 +0800 Subject: [PATCH 3/3] libbpf: Cleanup the legacy uprobe_event on failed add/attach_event() A potential scenario, when an error is returned after add_uprobe_event_legacy() in perf_event_uprobe_open_legacy(), or bpf_program__attach_perf_event_opts() in bpf_program__attach_uprobe_opts() returns an error, the uprobe_event that was previously created is not cleaned. So, with this patch, when an error is returned, fix this by adding remove_uprobe_event_legacy() Signed-off-by: Chuang Wang Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20220629151848.65587-4-nashuiliang@gmail.com --- tools/lib/bpf/libbpf.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 571acd614dce..cb49408eb298 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -10248,9 +10248,10 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe, } type = determine_uprobe_perf_type_legacy(probe_name, retprobe); if (type < 0) { + err = type; pr_warn("failed to determine legacy uprobe event id for %s:0x%zx: %d\n", - binary_path, offset, type); - return type; + binary_path, offset, err); + goto err_clean_legacy; } memset(&attr, 0, sizeof(attr)); @@ -10265,9 +10266,14 @@ static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe, if (pfd < 0) { err = -errno; pr_warn("legacy uprobe perf_event_open() failed: %d\n", err); - return err; + goto err_clean_legacy; } return pfd; + +err_clean_legacy: + /* Clear the newly added legacy uprobe_event */ + remove_uprobe_event_legacy(probe_name, retprobe); + return err; } /* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */ @@ -10601,7 +10607,7 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid, prog->name, retprobe ? "uretprobe" : "uprobe", binary_path, func_offset, libbpf_strerror_r(err, errmsg, sizeof(errmsg))); - goto err_out; + goto err_clean_legacy; } if (legacy) { struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link); @@ -10611,10 +10617,13 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid, perf_link->legacy_is_retprobe = retprobe; } return link; + +err_clean_legacy: + if (legacy) + remove_uprobe_event_legacy(legacy_probe, retprobe); err_out: free(legacy_probe); return libbpf_err_ptr(err); - } /* Format of u[ret]probe section definition supporting auto-attach: