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Message-ID: <273ef34f-3a67-64eb-e772-c46c390bf2f4@meta.com>
Date: Wed, 26 Apr 2023 22:27:32 -0700
From: Yonghong Song <yhs@...a.com>
To: Feng zhou <zhoufeng.zf@...edance.com>, martin.lau@...ux.dev,
ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
song@...nel.org, yhs@...com, john.fastabend@...il.com,
kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
jolsa@...nel.org, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com, mykolal@...com,
shuah@...nel.org
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
netdev@...r.kernel.org, linux-kselftest@...r.kernel.org,
yangzhenze@...edance.com, wangdongdong.6@...edance.com
Subject: Re: [PATCH bpf-next v3 2/2] selftests/bpf: Add testcase for
bpf_task_under_cgroup
On 4/26/23 7:30 PM, Feng zhou wrote:
> From: Feng Zhou <zhoufeng.zf@...edance.com>
>
> test_progs:
> Tests new kfunc bpf_task_under_cgroup().
>
> The bpf program saves the pid which call the getpgid syscall within a
> given cgroup to the remote_pid, which is convenient for the user-mode
> program to verify the test correctness.
>
> The user-mode program creates its own mount namespace, and mounts the
> cgroupsv2 hierarchy in there, call the getpgid syscall, then check if
> remote_pid and local_pid are equal.
>
> Signed-off-by: Feng Zhou <zhoufeng.zf@...edance.com>
> ---
> tools/testing/selftests/bpf/DENYLIST.s390x | 1 +
> .../bpf/prog_tests/task_under_cgroup.c | 47 +++++++++++++++++++
> .../selftests/bpf/progs/cgrp_kfunc_common.h | 1 +
> .../bpf/progs/test_task_under_cgroup.c | 37 +++++++++++++++
> 4 files changed, 86 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
> create mode 100644 tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
>
> diff --git a/tools/testing/selftests/bpf/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
> index c7463f3ec3c0..5061d9e24c16 100644
> --- a/tools/testing/selftests/bpf/DENYLIST.s390x
> +++ b/tools/testing/selftests/bpf/DENYLIST.s390x
> @@ -26,3 +26,4 @@ user_ringbuf # failed to find kernel BTF type ID of
> verif_stats # trace_vprintk__open_and_load unexpected error: -9 (?)
> xdp_bonding # failed to auto-attach program 'trace_on_entry': -524 (trampoline)
> xdp_metadata # JIT does not support calling kernel function (kfunc)
> +test_task_under_cgroup # JIT does not support calling kernel function (kfunc)
> diff --git a/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
> new file mode 100644
> index 000000000000..6d5709a8203d
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/task_under_cgroup.c
> @@ -0,0 +1,47 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Bytedance */
> +
> +#include <sys/syscall.h>
> +#include <test_progs.h>
> +#include <cgroup_helpers.h>
> +#include "test_task_under_cgroup.skel.h"
> +
> +#define FOO "/foo"
> +
> +void test_task_under_cgroup(void)
> +{
> + struct test_task_under_cgroup *skel;
> + int ret, foo = -1;
> +
> + foo = test__join_cgroup(FOO);
> + if (!ASSERT_OK(foo < 0, "cgroup_join_foo"))
> + return;
> +
> + skel = test_task_under_cgroup__open();
> + if (!ASSERT_OK_PTR(skel, "test_task_under_cgroup__open"))
> + goto cleanup;
> +
> + skel->rodata->local_pid = getpid();
> + skel->rodata->cgid = get_cgroup_id(FOO);
> +
> + ret = test_task_under_cgroup__load(skel);
> + if (!ASSERT_OK(ret, "test_task_under_cgroup__load"))
> + goto cleanup;
> +
> + ret = test_task_under_cgroup__attach(skel);
> + if (!ASSERT_OK(ret, "test_task_under_cgroup__attach"))
> + goto cleanup;
> +
> + syscall(SYS_getpgid);
> +
> + test_task_under_cgroup__detach(skel);
> +
> + ASSERT_EQ(skel->bss->remote_pid, skel->rodata->local_pid,
> + "test task_under_cgroup");
> +
> +cleanup:
> + if (foo >= 0)
> + close(foo);
> +
> + test_task_under_cgroup__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
> index 22914a70db54..001c416b42bc 100644
> --- a/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
> +++ b/tools/testing/selftests/bpf/progs/cgrp_kfunc_common.h
> @@ -26,6 +26,7 @@ struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level) __ksym;
> struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
> void bpf_rcu_read_lock(void) __ksym;
> void bpf_rcu_read_unlock(void) __ksym;
> +int bpf_task_under_cgroup(struct task_struct *task, struct cgroup *ancestor) __ksym;
return type 'long'?
>
> static inline struct __cgrps_kfunc_map_value *cgrps_kfunc_map_value_lookup(struct cgroup *cgrp)
> {
> diff --git a/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
> new file mode 100644
> index 000000000000..8f23a2933fde
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_task_under_cgroup.c
> @@ -0,0 +1,37 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2023 Bytedance */
> +
> +#include <vmlinux.h>
> +#include <bpf/bpf_tracing.h>
> +#include <bpf/bpf_helpers.h>
> +
> +#include "bpf_misc.h"
> +#include "cgrp_kfunc_common.h"
> +
> +const volatile int local_pid;
> +const volatile long cgid;
> +int remote_pid;
> +
> +SEC("fentry/" SYS_PREFIX "sys_getpgid")
> +int sys_getpgid(void *ctx)
> +{
> + struct cgroup *cgrp;
> +
> + if (local_pid != (bpf_get_current_pid_tgid() >> 32))
> + return 0;
> +
> + cgrp = bpf_cgroup_from_id(cgid);
> + if (!cgrp)
> + return 0;
> +
> + if (!bpf_task_under_cgroup(bpf_get_current_task_btf(), cgrp))
> + goto out;
The whole point of using bpf_task_under_cgroup() is to test a
non-current task is under a particular cgroup.
Tracing kernel function enqueue_task_fair() is an option, but it
may be inlined with certain compilers as enqueue_task_fair() is
a static function. Also, the 'task' argument in enqueue_task_fair()
is not trusted, could be null ptr and not rcu safe as well.
We could promote 'task' in enqueue_task_fair() by:
- checking NULL ptr, if not
- increase reference count by 1 if current reference count is not 0
(using bpf_task_acquire kfunc)
- if reference count can be increased, it becomes trusted, and
then bpf_task_under_cgroup() can be used.
Could you try this approach or even better if there is another
non-static function also having a task (not the current task)?
> +
> + remote_pid = local_pid;
> +
> +out:
> + bpf_cgroup_release(cgrp);
> + return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
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