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

Jiri Olsa
2023-06-23T08:19:28Z

On Thu, Jun 22, 2023 at 05:18:05PM -0700, Andrii Nakryiko wrote:
> 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;` ;)

ugh, yes, will fix

> > 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?

ok, perhaps we could move there the whole switch, will check

>
> > @@ -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?

I won't pretend I understand what rcu_read_lock_trace does ;-)

I tried to follow bpf_prog_run_array_sleepable where it's called
unconditionally for both sleepable and non-sleepable progs

there are conditional rcu_read_un/lock calls later on

I will check

>
> > + 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?

true :-\ will add the uref_ctr_offsets check

>
> > +
> > + 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 path won't call release callback so we have to do that

I think I can add simple selftest to have this path covered

thanks,
jirka

>
> > + 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;
> > +}
>
> …