Re: [PATCH v3 bpf-next 3/3] selftests/bpf: add custom SEC() handling selftest

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On Fri, 11 Feb 2022, Andrii Nakryiko wrote:

> Add a selftest validating various aspects of libbpf's handling of custom
> SEC() handlers. It also demonstrates how libraries can ensure very early
> callbacks registration and unregistration using
> __attribute__((constructor))/__attribute__((destructor)) functions.
> 
> Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>

Thanks for adding the additional tests, looks great!

> ---
>  .../bpf/prog_tests/custom_sec_handlers.c      | 176 ++++++++++++++++++
>  .../bpf/progs/test_custom_sec_handlers.c      |  63 +++++++
>  2 files changed, 239 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/custom_sec_handlers.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_custom_sec_handlers.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/custom_sec_handlers.c b/tools/testing/selftests/bpf/prog_tests/custom_sec_handlers.c
> new file mode 100644
> index 000000000000..28264528280d
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/custom_sec_handlers.c
> @@ -0,0 +1,176 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2022 Facebook */
> +
> +#include <test_progs.h>
> +#include "test_custom_sec_handlers.skel.h"
> +
> +#define COOKIE_ABC1 1
> +#define COOKIE_ABC2 2
> +#define COOKIE_CUSTOM 3
> +#define COOKIE_FALLBACK 4
> +#define COOKIE_KPROBE 5
> +
> +static int custom_init_prog(struct bpf_program *prog, long cookie)
> +{
> +	if (cookie == COOKIE_ABC1)
> +		bpf_program__set_autoload(prog, false);
> +
> +	return 0;
> +}
> +
> +static int custom_preload_prog(struct bpf_program *prog,
> +			       struct bpf_prog_load_opts *opts, long cookie)
> +{
> +	if (cookie == COOKIE_FALLBACK)
> +		opts->prog_flags |= BPF_F_SLEEPABLE;
> +	else if (cookie == COOKIE_ABC1)
> +		ASSERT_FALSE(true, "unexpected preload for abc");
> +
> +	return 0;
> +}
> +
> +static int custom_attach_prog(const struct bpf_program *prog, long cookie,
> +			      struct bpf_link **link)
> +{
> +	switch (cookie) {
> +	case COOKIE_ABC2:
> +		*link = bpf_program__attach_raw_tracepoint(prog, "sys_enter");
> +		return libbpf_get_error(*link);
> +	case COOKIE_CUSTOM:
> +		*link = bpf_program__attach_tracepoint(prog, "syscalls", "sys_enter_nanosleep");
> +		return libbpf_get_error(*link);
> +	case COOKIE_KPROBE:
> +	case COOKIE_FALLBACK:
> +		/* no auto-attach for SEC("xyz") and SEC("kprobe") */
> +		*link = NULL;
> +		return 0;
> +	default:
> +		ASSERT_FALSE(true, "unexpected cookie");
> +		return -EINVAL;
> +	}
> +}
> +
> +static int abc1_id;
> +static int abc2_id;
> +static int custom_id;
> +static int fallback_id;
> +static int kprobe_id;
> +
> +__attribute__((constructor))
> +static void register_sec_handlers(void)
> +{
> +	LIBBPF_OPTS(libbpf_prog_handler_opts, abc1_opts,
> +		.cookie = COOKIE_ABC1,
> +		.init_fn = custom_init_prog,
> +		.preload_fn = custom_preload_prog,
> +		.attach_fn = NULL,
> +	);
> +	LIBBPF_OPTS(libbpf_prog_handler_opts, abc2_opts,
> +		.cookie = COOKIE_ABC2,
> +		.init_fn = custom_init_prog,
> +		.preload_fn = custom_preload_prog,
> +		.attach_fn = custom_attach_prog,
> +	);
> +	LIBBPF_OPTS(libbpf_prog_handler_opts, custom_opts,
> +		.cookie = COOKIE_CUSTOM,
> +		.init_fn = NULL,
> +		.preload_fn = NULL,
> +		.attach_fn = custom_attach_prog,
> +	);
> +
> +	abc1_id = libbpf_register_prog_handler("abc", BPF_PROG_TYPE_RAW_TRACEPOINT, 0, &abc1_opts);
> +	abc2_id = libbpf_register_prog_handler("abc/", BPF_PROG_TYPE_RAW_TRACEPOINT, 0, &abc2_opts);
> +	custom_id = libbpf_register_prog_handler("custom+", BPF_PROG_TYPE_TRACEPOINT, 0, &custom_opts);
> +}
> +
> +__attribute__((destructor))
> +static void unregister_sec_handlers(void)
> +{
> +	libbpf_unregister_prog_handler(abc1_id);
> +	libbpf_unregister_prog_handler(abc2_id);
> +	libbpf_unregister_prog_handler(custom_id);
> +}
> +
> +void test_custom_sec_handlers(void)
> +{
> +	LIBBPF_OPTS(libbpf_prog_handler_opts, opts,
> +		.init_fn = custom_init_prog,
> +		.preload_fn = custom_preload_prog,
> +		.attach_fn = custom_attach_prog,
> +	);
> +	struct test_custom_sec_handlers* skel;
> +	int err;
> +
> +	ASSERT_GT(abc1_id, 0, "abc1_id");
> +	ASSERT_GT(abc2_id, 0, "abc2_id");
> +	ASSERT_GT(custom_id, 0, "custom_id");
> +
> +	/* override libbpf's handle of SEC("kprobe/...") but also allow pure
> +	 * SEC("kprobe") due to "kprobe+" specifier. Register it as
> +	 * TRACEPOINT, just for fun.
> +	 */
> +	opts.cookie = COOKIE_KPROBE;
> +	kprobe_id = libbpf_register_prog_handler("kprobe+", BPF_PROG_TYPE_TRACEPOINT, 0, &opts);
> +	/* fallback treats everything as BPF_PROG_TYPE_SYSCALL program to test
> +	 * setting custom BPF_F_SLEEPABLE bit in preload handler
> +	 */
> +	opts.cookie = COOKIE_FALLBACK;
> +	fallback_id = libbpf_register_prog_handler(NULL, BPF_PROG_TYPE_SYSCALL, 0, &opts);
> +
> +	if (!ASSERT_GT(fallback_id, 0, "fallback_id") /* || !ASSERT_GT(kprobe_id, 0, "kprobe_id")*/) {
> +		if (fallback_id > 0)
> +			libbpf_unregister_prog_handler(fallback_id);
> +		if (kprobe_id > 0)
> +			libbpf_unregister_prog_handler(kprobe_id);
> +		return;
> +	}
> +
> +	/* open skeleton and validate assumptions */
> +	skel = test_custom_sec_handlers__open();
> +	if (!ASSERT_OK_PTR(skel, "skel_open"))
> +		goto cleanup;
> +
> +	ASSERT_EQ(bpf_program__type(skel->progs.abc1), BPF_PROG_TYPE_RAW_TRACEPOINT, "abc1_type");
> +	ASSERT_FALSE(bpf_program__autoload(skel->progs.abc1), "abc1_autoload");
> +
> +	ASSERT_EQ(bpf_program__type(skel->progs.abc2), BPF_PROG_TYPE_RAW_TRACEPOINT, "abc2_type");
> +	ASSERT_EQ(bpf_program__type(skel->progs.custom1), BPF_PROG_TYPE_TRACEPOINT, "custom1_type");
> +	ASSERT_EQ(bpf_program__type(skel->progs.custom2), BPF_PROG_TYPE_TRACEPOINT, "custom2_type");
> +	ASSERT_EQ(bpf_program__type(skel->progs.kprobe1), BPF_PROG_TYPE_TRACEPOINT, "kprobe1_type");
> +	ASSERT_EQ(bpf_program__type(skel->progs.xyz), BPF_PROG_TYPE_SYSCALL, "xyz_type");
> +
> +	skel->rodata->my_pid = getpid();
> +
> +	/* now attempt to load everything */
> +	err = test_custom_sec_handlers__load(skel);
> +	if (!ASSERT_OK(err, "skel_load"))
> +		goto cleanup;
> +
> +	/* now try to auto-attach everything */
> +	err = test_custom_sec_handlers__attach(skel);
> +	if (!ASSERT_OK(err, "skel_attach"))
> +		goto cleanup;
> +
> +	skel->links.xyz = bpf_program__attach(skel->progs.kprobe1);
> +	ASSERT_EQ(errno, EOPNOTSUPP, "xyz_attach_err");
> +	ASSERT_ERR_PTR(skel->links.xyz, "xyz_attach");
> +
> +	/* trigger programs */
> +	usleep(1);
> +
> +	/* SEC("abc") is set to not auto-loaded */
> +	ASSERT_FALSE(skel->bss->abc1_called, "abc1_called");
> +	ASSERT_TRUE(skel->bss->abc2_called, "abc2_called");
> +	ASSERT_TRUE(skel->bss->custom1_called, "custom1_called");
> +	ASSERT_TRUE(skel->bss->custom2_called, "custom2_called");
> +	/* SEC("kprobe") shouldn't be auto-attached */
> +	ASSERT_FALSE(skel->bss->kprobe1_called, "kprobe1_called");
> +	/* SEC("xyz") shouldn't be auto-attached */
> +	ASSERT_FALSE(skel->bss->xyz_called, "xyz_called");
> +
> +cleanup:
> +	test_custom_sec_handlers__destroy(skel);
> +
> +	ASSERT_OK(libbpf_unregister_prog_handler(fallback_id), "unregister_fallback");
> +	ASSERT_OK(libbpf_unregister_prog_handler(kprobe_id), "unregister_kprobe");
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_custom_sec_handlers.c b/tools/testing/selftests/bpf/progs/test_custom_sec_handlers.c
> new file mode 100644
> index 000000000000..4061f701ca50
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_custom_sec_handlers.c
> @@ -0,0 +1,63 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2022 Facebook */
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +const volatile int my_pid;
> +
> +bool abc1_called;
> +bool abc2_called;
> +bool custom1_called;
> +bool custom2_called;
> +bool kprobe1_called;
> +bool xyz_called;
> +
> +SEC("abc")
> +int abc1(void *ctx)
> +{
> +	abc1_called = true;
> +	return 0;
> +}
> +
> +SEC("abc/whatever")
> +int abc2(void *ctx)
> +{
> +	abc2_called = true;
> +	return 0;
> +}
> +
> +SEC("custom")
> +int custom1(void *ctx)
> +{
> +	custom1_called = true;
> +	return 0;
> +}
> +
> +SEC("custom/something")
> +int custom2(void *ctx)
> +{
> +	custom2_called = true;
> +	return 0;
> +}
> +
> +SEC("kprobe")
> +int kprobe1(void *ctx)
> +{
> +	kprobe1_called = true;
> +	return 0;
> +}
> +
> +SEC("xyz/blah")
> +int xyz(void *ctx)
> +{
> +	int whatever;
> +
> +	/* use sleepable helper, custom handler should set sleepable flag */
> +	bpf_copy_from_user(&whatever, sizeof(whatever), NULL);
> +	xyz_called = true;
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> -- 
> 2.30.2
> 
> 



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