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From: Hao Luo <haoluo@google.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	open list <linux-kernel@vger.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>, Shuah Khan <shuah@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andriin@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Quentin Monnet <quentin@isovalent.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>, Andrey Ignatov <rdna@fb.com>,
	Jakub Sitnicki <jakub@cloudflare.com>
Subject: Re: [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr()
Date: Tue, 1 Sep 2020 12:47:02 -0700	[thread overview]
Message-ID: <CA+khW7iP+BsXnNg0E-K3npR74FqV0b+oHo9j27ymKWobi-QBVw@mail.gmail.com> (raw)
In-Reply-To: <CAEf4Bza5+m72JQ1Q3a2GRetGB7C-Zemvd-ib0u_VKC2nrYkgdQ@mail.gmail.com>

On Tue, Sep 1, 2020 at 11:12 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Thu, Aug 27, 2020 at 8:42 PM Hao Luo <haoluo@google.com> wrote:
> >
[...]
> > > >
> > > > -extern const struct rq runqueues __ksym; /* struct type global var. */
> > > > +extern const struct rq runqueues __ksym; /* struct type percpu var. */
> > > >  extern const int bpf_prog_active __ksym; /* int type global var. */
> > > > +extern const unsigned long process_counts __ksym; /* int type percpu var. */
> > > >
> > > >  SEC("raw_tp/sys_enter")
> > > >  int handler(const void *ctx)
> > > >  {
> > > > +       struct rq *rq;
> > > > +       unsigned long *count;
> > > > +
> > > >         out__runqueues = (__u64)&runqueues;
> > > >         out__bpf_prog_active = (__u64)&bpf_prog_active;
> > > >
> > > > +       rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, 1);
> > > > +       if (rq)
> > > > +               out__rq_cpu = rq->cpu;
> > >
> > > this is awesome!
> > >
> > > Are there any per-cpu variables that are arrays? Would be nice to test
> > > those too.
> > >
> > >
> >
> > There are currently per-cpu arrays, but not common. There is a
> > 'pmc_prev_left' in arch/x86, I can add that in this test.
>
> arch-specific variables are bad, because selftests will be failing on
> other architectures; let's not do this then.
>

Yeah, no problem. Though not going to add this arch-specific variable
in the posted patches, I tried array-typed ksyms locally in my test
environment. It worked fine, except that the array size is not
checked. For instance, if there is a percpu array in kernel as

DEFINE_PER_CPU(u32[64], foo);

we can declare a ksym of different size and it passes libbpf checks
and kernel verification.

extern u32 foo[128] __ksyms;

It seems that bpf_core_types_are_compat() doesn't check nr_elem. But
it seems the kernel verifier does check out-of-bounds accesses, so
this may not be a real problem. Just want to list what I saw.

> >
> > [...]

      reply	other threads:[~2020-09-01 19:47 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19 22:40 [PATCH bpf-next v1 0/8] bpf: BTF support for ksyms Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 1/8] bpf: Introduce pseudo_btf_id Hao Luo
2020-08-20 15:22   ` Yonghong Song
2020-08-20 17:04     ` Hao Luo
2020-08-25  0:05     ` Hao Luo
2020-08-25  0:43       ` Yonghong Song
2020-08-20 16:43   ` Yonghong Song
2020-08-20 21:53   ` Alexei Starovoitov
2020-08-21  2:22     ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 2/8] bpf: Propagate BPF_PSEUDO_BTF_ID to uapi headers in /tools Hao Luo
2020-08-20 16:44   ` Yonghong Song
2020-08-19 22:40 ` [PATCH bpf-next v1 3/8] bpf: Introduce help function to validate ksym's type Hao Luo
2020-08-20 17:20   ` Yonghong Song
2020-08-21 21:50     ` Andrii Nakryiko
2020-08-22  0:43       ` Hao Luo
2020-08-22  2:43         ` Andrii Nakryiko
2020-08-22  7:04           ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 4/8] bpf/libbpf: BTF support for typed ksyms Hao Luo
2020-08-21 22:37   ` Andrii Nakryiko
2020-08-27 22:29     ` Hao Luo
2020-09-01 18:11       ` Andrii Nakryiko
2020-09-01 20:35         ` Hao Luo
2020-09-01 23:54           ` Andrii Nakryiko
2020-09-02  0:46             ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 5/8] bpf/selftests: ksyms_btf to test " Hao Luo
2020-08-20 17:28   ` Yonghong Song
2020-08-21 23:03     ` Andrii Nakryiko
2020-08-22  7:26       ` Hao Luo
2020-08-22  7:35         ` Andrii Nakryiko
2020-08-19 22:40 ` [PATCH bpf-next v1 6/8] bpf: Introduce bpf_per_cpu_ptr() Hao Luo
2020-08-22  3:26   ` Andrii Nakryiko
2020-08-22  3:31     ` Andrii Nakryiko
2020-08-22  7:49       ` Hao Luo
2020-08-22  7:55         ` Andrii Nakryiko
2020-08-25  1:03           ` Hao Luo
2020-08-19 22:40 ` [PATCH bpf-next v1 7/8] bpf: Propagate bpf_per_cpu_ptr() to /tools Hao Luo
2020-08-20 17:30   ` Yonghong Song
2020-08-19 22:40 ` [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr() Hao Luo
2020-08-22  3:30   ` Andrii Nakryiko
2020-08-28  3:42     ` Hao Luo
2020-09-01 18:12       ` Andrii Nakryiko
2020-09-01 19:47         ` Hao Luo [this message]

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