Re: [PATCHv2 bpf-next 01/24] bpf: Add multi uprobe link

Andrii Nakryiko
2023-06-23T00:18:20Z

On Tue, Jun 20, 2023 at 1:36 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Adding new multi uprobe link that allows to attach bpf program
> to multiple uprobes.
>
> Uprobes to attach are specified via new link_create uprobe_multi
> union:
>
> struct {
> __u32 flags;
> __u32 cnt;
> __aligned_u64 path;
> __aligned_u64 offsets;
> __aligned_u64 ref_ctr_offsets;
> } uprobe_multi;
>
> Uprobes are defined for single binary specified in path and multiple
> calling sites specified in offsets array with optional reference
> counters specified in ref_ctr_offsets array. All specified arrays
> have length of 'cnt'.
>
> The 'flags' supports single bit for now that marks the uprobe as
> return probe.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> include/linux/trace_events.h | 6 +
> include/uapi/linux/bpf.h | 14 ++
> kernel/bpf/syscall.c | 12 +-
> kernel/trace/bpf_trace.c | 237 +++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 14 ++
> 5 files changed, 281 insertions(+), 2 deletions(-)
>

[...]

> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index a75c54b6f8a3..a96e46cd407e 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3516,6 +3516,11 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
> return prog->enforce_expected_attach_type &&
> prog->expected_attach_type != attach_type ?
> -EINVAL : 0;
> + case BPF_PROG_TYPE_KPROBE:
> + if (prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI &&
> + attach_type != BPF_TRACE_KPROBE_MULTI)

should this be UPROBE_MULTI? this looks like your recent bug fix,
which already landed

> + return -EINVAL;
> + fallthrough;

and I replaced this with `return 0;` ;)
> default:
> return 0;
> }
> @@ -4681,7 +4686,8 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
> break;
> case BPF_PROG_TYPE_KPROBE:
> if (attr->link_create.attach_type != BPF_PERF_EVENT &&
> - attr->link_create.attach_type != BPF_TRACE_KPROBE_MULTI) {
> + attr->link_create.attach_type != BPF_TRACE_KPROBE_MULTI &&
> + attr->link_create.attach_type != BPF_TRACE_UPROBE_MULTI) {
> ret = -EINVAL;
> goto out;
> }

should this be moved into bpf_prog_attach_check_attach_type() and
unify these checks?

> @@ -4748,8 +4754,10 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
> case BPF_PROG_TYPE_KPROBE:
> if (attr->link_create.attach_type == BPF_PERF_EVENT)
> ret = bpf_perf_link_attach(attr, prog);
> - else
> + else if (attr->link_create.attach_type == BPF_TRACE_KPROBE_MULTI)
> ret = bpf_kprobe_multi_link_attach(attr, prog);
> + else if (attr->link_create.attach_type == BPF_TRACE_UPROBE_MULTI)
> + ret = bpf_uprobe_multi_link_attach(attr, prog);
> break;
> default:
> ret = -EINVAL;

[...]

> +static void bpf_uprobe_unregister(struct path *path, struct bpf_uprobe *uprobes,
> + u32 cnt)
> +{
> + u32 i;
> +
> + for (i = 0; i < cnt; i++) {
> + uprobe_unregister(d_real_inode(path->dentry), uprobes[i].offset,
> + &uprobes[i].consumer);
> + }
> +}
> +
> +static void bpf_uprobe_multi_link_release(struct bpf_link *link)
> +{
> + struct bpf_uprobe_multi_link *umulti_link;
> +
> + umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
> + bpf_uprobe_unregister(&umulti_link->path, umulti_link->uprobes, umulti_link->cnt);
> + path_put(&umulti_link->path);
> +}
> +
> +static void bpf_uprobe_multi_link_dealloc(struct bpf_link *link)
> +{
> + struct bpf_uprobe_multi_link *umulti_link;
> +
> + umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
> + kvfree(umulti_link->uprobes);
> + kfree(umulti_link);
> +}
> +
> +static const struct bpf_link_ops bpf_uprobe_multi_link_lops = {
> + .release = bpf_uprobe_multi_link_release,
> + .dealloc = bpf_uprobe_multi_link_dealloc,
> +};
> +
> +static int uprobe_prog_run(struct bpf_uprobe *uprobe,
> + unsigned long entry_ip,
> + struct pt_regs *regs)
> +{
> + struct bpf_uprobe_multi_link *link = uprobe->link;
> + struct bpf_uprobe_multi_run_ctx run_ctx = {
> + .entry_ip = entry_ip,
> + };
> + struct bpf_prog *prog = link->link.prog;
> + struct bpf_run_ctx *old_run_ctx;
> + int err = 0;
> +
> + might_fault();
> +
> + rcu_read_lock_trace();

we don't need this if uprobe is not sleepable, right? why unconditional then?

> + migrate_disable();
> +
> + if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1))
> + goto out;
> +
> + old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx);
> +
> + if (!prog->aux->sleepable)
> + rcu_read_lock();
> +
> + err = bpf_prog_run(link->link.prog, regs);
> +
> + if (!prog->aux->sleepable)
> + rcu_read_unlock();
> +
> + bpf_reset_run_ctx(old_run_ctx);
> +
> +out:
> + __this_cpu_dec(bpf_prog_active);
> + migrate_enable();
> + rcu_read_unlock_trace();
> + return err;
> +}
> +

[...]

> +
> + err = kern_path(name, LOOKUP_FOLLOW, &path);
> + kfree(name);
> + if (err)
> + return err;
> +
> + if (!d_is_reg(path.dentry)) {
> + err = -EINVAL;
> + goto error_path_put;
> + }
> +
> + err = -ENOMEM;
> +
> + link = kzalloc(sizeof(*link), GFP_KERNEL);
> + uprobes = kvcalloc(cnt, sizeof(*uprobes), GFP_KERNEL);
> + ref_ctr_offsets = kvcalloc(cnt, sizeof(*ref_ctr_offsets), GFP_KERNEL);

ref_ctr_offsets is optional, but we'll unconditionally allocate this array?

> +
> + if (!uprobes || !ref_ctr_offsets || !link)
> + goto error_free;
> +
> + for (i = 0; i < cnt; i++) {
> + if (uref_ctr_offsets && __get_user(ref_ctr_offset, uref_ctr_offsets + i)) {
> + err = -EFAULT;
> + goto error_free;
> + }
> + if (__get_user(offset, uoffsets + i)) {
> + err = -EFAULT;
> + goto error_free;
> + }
> +
> + uprobes[i].offset = offset;
> + uprobes[i].link = link;
> +
> + if (flags & BPF_F_UPROBE_MULTI_RETURN)
> + uprobes[i].consumer.ret_handler = uprobe_multi_link_ret_handler;
> + else
> + uprobes[i].consumer.handler = uprobe_multi_link_handler;
> +
> + ref_ctr_offsets[i] = ref_ctr_offset;
> + }
> +
> + link->cnt = cnt;
> + link->uprobes = uprobes;
> + link->path = path;
> +
> + bpf_link_init(&link->link, BPF_LINK_TYPE_UPROBE_MULTI,
> + &bpf_uprobe_multi_link_lops, prog);
> +
> + err = bpf_link_prime(&link->link, &link_primer);
> + if (err)
> + goto error_free;
> +
> + for (i = 0; i < cnt; i++) {
> + err = uprobe_register_refctr(d_real_inode(link->path.dentry),
> + uprobes[i].offset, ref_ctr_offsets[i],
> + &uprobes[i].consumer);
> + if (err) {
> + bpf_uprobe_unregister(&path, uprobes, i);

bpf_link_cleanup() will do this through
bpf_uprobe_multi_link_release(), no? So you are double unregistering?
Either drop cnt to zero, or just don't do this here? Latter is better,
IMO.

> + bpf_link_cleanup(&link_primer);
> + kvfree(ref_ctr_offsets);
> + return err;
> + }
> + }
> +
> + kvfree(ref_ctr_offsets);
> + return bpf_link_settle(&link_primer);
> +
> +error_free:
> + kvfree(ref_ctr_offsets);
> + kvfree(uprobes);
> + kfree(link);
> +error_path_put:
> + path_put(&path);
> + return err;
> +}
> +#else /* !CONFIG_UPROBES */
> +int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> +{
> + return -EOPNOTSUPP;
> +} …