[bpf,v2,1/2] selftests/bpf: add a test for subprogram extables

In certain situations a program with subprograms may have a NULL
extable entry.  This should not happen, and when it does, it turns a
single trap into multiple.  Add a test case for further debugging and to
prevent regressions.  N.b: without any other patches this can panic or
oops a kernel.

Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
---
 .../bpf/prog_tests/subprogs_extable.c         | 35 +++++++++
 .../bpf/progs/test_subprogs_extable.c         | 71 +++++++++++++++++++
 2 files changed, 106 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs_extable.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs_extable.c

On 6/7/23 2:04 PM, Krister Johansen wrote:
> In certain situations a program with subprograms may have a NULL
> extable entry.  This should not happen, and when it does, it turns a
> single trap into multiple.  Add a test case for further debugging and to
> prevent regressions.  N.b: without any other patches this can panic or
> oops a kernel.
> 
> Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
> ---
>   .../bpf/prog_tests/subprogs_extable.c         | 35 +++++++++
>   .../bpf/progs/test_subprogs_extable.c         | 71 +++++++++++++++++++
>   2 files changed, 106 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs_extable.c
>   create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs_extable.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/subprogs_extable.c b/tools/testing/selftests/bpf/prog_tests/subprogs_extable.c
> new file mode 100644
> index 000000000000..18169b7eedf8
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/subprogs_extable.c
> @@ -0,0 +1,35 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2020 Facebook */

This copyright is not correct.

> +
> +#include <test_progs.h>
> +#include <stdbool.h>

stdbool.h is not needed.

> +#include "test_subprogs_extable.skel.h"
> +
> +static int duration;
> +
> +void test_subprogs_extable(void)
> +{
> +	const int READ_SZ = 456;
> +	struct test_subprogs_extable *skel;
> +	int err;
> +
> +	skel = test_subprogs_extable__open();
> +	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
> +		return;

Please use ASSERT_* macros instead of CHECK macro. The same for below.
See some examples in prog_tests directory.

> +
> +	err = test_subprogs_extable__load(skel);
> +	if (CHECK(err, "skel_load", "failed to load skeleton\n"))
> +		return;

goto cleanup;

> +
> +	err = test_subprogs_extable__attach(skel);
> +	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
> +		goto cleanup;
> +
> +	/* trigger tracepoint */
> +	ASSERT_OK(trigger_module_test_read(READ_SZ), "trigger_read");
> +
> +	test_subprogs_extable__detach(skel);
> +
> +cleanup:
> +	test_subprogs_extable__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_subprogs_extable.c b/tools/testing/selftests/bpf/progs/test_subprogs_extable.c
> new file mode 100644
> index 000000000000..408137eaaa07
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_subprogs_extable.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2020 Facebook */

the above copyright is not correct.

> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include <bpf/bpf_core_read.h>

There is no CORE related operation in the program. The above header is 
not needed.

> +#include "../bpf_testmod/bpf_testmod.h"

This one is not needed too.

> +
> +struct {
> +	__uint(type, BPF_MAP_TYPE_ARRAY);
> +	__uint(max_entries, 8);
> +	__type(key, __u32);
> +	__type(value, __u64);
> +} test_array SEC(".maps");
> +
> +static __u64 test_cb(struct bpf_map *map, __u32 *key, __u64 *val, void *data)
> +{
> +	return 1;
> +}
> +
> +static __u64 test_cb2(struct bpf_map *map, __u32 *key, __u64 *val, void *data)
> +{
> +	return 1;
> +}
> +
> +static __u64 test_cb3(struct bpf_map *map, __u32 *key, __u64 *val, void *data)
> +{
> +	return 1;
> +}

We can just have one test_cb and used for all programs, right?
Or more subprograms increase the chance of the test failure?

> +
> +SEC("fexit/bpf_testmod_return_ptr")
> +int BPF_PROG(handle_fexit_ret_subprogs, int arg, struct file *ret)
> +{
> +	long buf = 0;
> +
> +	bpf_probe_read_kernel(&buf, 8, ret);
> +	bpf_probe_read_kernel(&buf, 8, (char *)ret + 256);

The above bpf_probe_read_kernel() things are not necessary, right?

> +	*(volatile long long *)ret;

just 'volatile long' should be enough.

> +	*(volatile int *)&ret->f_mode;
> +	bpf_for_each_map_elem(&test_array, test_cb, NULL, 0);
> +	return 0;
> +}
> +
> +SEC("fexit/bpf_testmod_return_ptr")
> +int BPF_PROG(handle_fexit_ret_subprogs2, int arg, struct file *ret)
> +{
> +	long buf = 0;
> +
> +	bpf_probe_read_kernel(&buf, 8, ret);
> +	bpf_probe_read_kernel(&buf, 8, (char *)ret + 256);
> +	*(volatile long long *)ret;
> +	*(volatile int *)&ret->f_mode;
> +	bpf_for_each_map_elem(&test_array, test_cb2, NULL, 0);
> +	return 0;
> +}
> +
> +SEC("fexit/bpf_testmod_return_ptr")
> +int BPF_PROG(handle_fexit_ret_subprogs3, int arg, struct file *ret)
> +{
> +	long buf = 0;
> +
> +	bpf_probe_read_kernel(&buf, 8, ret);
> +	bpf_probe_read_kernel(&buf, 8, (char *)ret + 256);
> +	*(volatile long long *)ret;
> +	*(volatile int *)&ret->f_mode;
> +	bpf_for_each_map_elem(&test_array, test_cb3, NULL, 0);
> +	return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";

On 6/7/23 2:04 PM, Krister Johansen wrote:
> In certain situations a program with subprograms may have a NULL
> extable entry.  This should not happen, and when it does, it turns a
> single trap into multiple.  Add a test case for further debugging and to
> prevent regressions.  N.b: without any other patches this can panic or
> oops a kernel.

Also, it would be great if you can show the kernel oops stack trace.

> 
> Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
> ---
>   .../bpf/prog_tests/subprogs_extable.c         | 35 +++++++++
>   .../bpf/progs/test_subprogs_extable.c         | 71 +++++++++++++++++++
>   2 files changed, 106 insertions(+)
>   create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs_extable.c
>   create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs_extable.c
> 
[...]

On Thu, Jun 8, 2023 at 10:40 AM Yonghong Song <yhs@meta.com> wrote:
>
>
>
> On 6/7/23 2:04 PM, Krister Johansen wrote:
> > In certain situations a program with subprograms may have a NULL
> > extable entry.  This should not happen, and when it does, it turns a
> > single trap into multiple.  Add a test case for further debugging and to
> > prevent regressions.  N.b: without any other patches this can panic or
> > oops a kernel.
>
> Also, it would be great if you can show the kernel oops stack trace.

+1

Also please reorder the patches.
patch 1 - fix
patch 2 - test for the fix.