Re: [PATCH bpf-next v5 12/17] selftests/bpf: add tests for bpf_hid_hw_request

Benjamin Tissoires
2022-05-19T12:13:04Z

On Thu, May 19, 2022 at 12:20 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Thu, May 19, 2022 at 02:29:19AM IST, Benjamin Tissoires wrote:
> > Add tests for the newly implemented function.
> > We test here only the GET_REPORT part because the other calls are pure
> > HID protocol and won't infer the result of the test of the bpf hook.
> >
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> >
> > ---
> >
> > changes in v5:
> > - use the new hid_bpf_allocate_context() API
> > - remove the need for ctx_in for syscall TEST_RUN
> >
> > changes in v3:
> > - use the new hid_get_data API
> > - directly use HID_FEATURE_REPORT and HID_REQ_GET_REPORT from uapi
> >
> > changes in v2:
> > - split the series by bpf/libbpf/hid/selftests and samples
> > ---
> > tools/testing/selftests/bpf/prog_tests/hid.c | 114 ++++++++++++++++---
> > tools/testing/selftests/bpf/progs/hid.c | 59 ++++++++++
> > 2 files changed, 155 insertions(+), 18 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/hid.c b/tools/testing/selftests/bpf/prog_tests/hid.c
> > index 47bc0a30c275..54c0a0fcd54d 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/hid.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/hid.c
> > @@ -77,12 +77,23 @@ static unsigned char rdesc[] = {
> > 0xc0, /* END_COLLECTION */
> > };
> >
> > +static u8 feature_data[] = { 1, 2 };
> > +
> > struct attach_prog_args {
> > int prog_fd;
> > unsigned int hid;
> > int retval;
> > };
> >
> > +struct hid_hw_request_syscall_args {
> > + __u8 data[10];
> > + unsigned int hid;
> > + int retval;
> > + size_t size;
> > + enum hid_report_type type;
> > + __u8 request_type;
> > +};
> > +
> > static pthread_mutex_t uhid_started_mtx = PTHREAD_MUTEX_INITIALIZER;
> > static pthread_cond_t uhid_started = PTHREAD_COND_INITIALIZER;
> >
> > @@ -142,7 +153,7 @@ static void destroy(int fd)
> >
> > static int uhid_event(int fd)
> > {
> > - struct uhid_event ev;
> > + struct uhid_event ev, answer;
> > ssize_t ret;
> >
> > memset(&ev, 0, sizeof(ev));
> > @@ -183,6 +194,15 @@ static int uhid_event(int fd)
> > break;
> > case UHID_GET_REPORT:
> > fprintf(stderr, "UHID_GET_REPORT from uhid-dev\n");
> > +
> > + answer.type = UHID_GET_REPORT_REPLY;
> > + answer.u.get_report_reply.id = ev.u.get_report.id;
> > + answer.u.get_report_reply.err = ev.u.get_report.rnum == 1 ? 0 : -EIO;
> > + answer.u.get_report_reply.size = sizeof(feature_data);
> > + memcpy(answer.u.get_report_reply.data, feature_data, sizeof(feature_data));
> > +
> > + uhid_write(fd, &answer);
> > +
> > break;
> > case UHID_SET_REPORT:
> > fprintf(stderr, "UHID_SET_REPORT from uhid-dev\n");
> > @@ -391,6 +411,7 @@ static int open_hidraw(int dev_id)
> > struct test_params {
> > struct hid *skel;
> > int hidraw_fd;
> > + int hid_id;
> > };
> >
> > static int prep_test(int dev_id, const char *prog_name, struct test_params *test_data)
> > @@ -419,27 +440,33 @@ static int prep_test(int dev_id, const char *prog_name, struct test_params *test
> > if (!ASSERT_OK_PTR(hid_skel, "hid_skel_open"))
> > goto cleanup;
> >
> > - prog = bpf_object__find_program_by_name(*hid_skel->skeleton->obj, prog_name);
> > - if (!ASSERT_OK_PTR(prog, "find_prog_by_name"))
> > - goto cleanup;
> > + if (prog_name) {
> > + prog = bpf_object__find_program_by_name(*hid_skel->skeleton->obj, prog_name);
> > + if (!ASSERT_OK_PTR(prog, "find_prog_by_name"))
> > + goto cleanup;
> >
> > - bpf_program__set_autoload(prog, true);
> > + bpf_program__set_autoload(prog, true);
> >
> > - err = hid__load(hid_skel);
> > - if (!ASSERT_OK(err, "hid_skel_load"))
> > - goto cleanup;
> > + err = hid__load(hid_skel);
> > + if (!ASSERT_OK(err, "hid_skel_load"))
> > + goto cleanup;
> >
> > - attach_fd = bpf_program__fd(hid_skel->progs.attach_prog);
> > - if (!ASSERT_GE(attach_fd, 0, "locate attach_prog")) {
> > - err = attach_fd;
> > - goto cleanup;
> > - }
> > + attach_fd = bpf_program__fd(hid_skel->progs.attach_prog);
> > + if (!ASSERT_GE(attach_fd, 0, "locate attach_prog")) {
> > + err = attach_fd;
> > + goto cleanup;
> > + }
> >
> > - args.prog_fd = bpf_program__fd(prog);
> > - err = bpf_prog_test_run_opts(attach_fd, &tattr);
> > - snprintf(buf, sizeof(buf), "attach_hid(%s)", prog_name);
> > - if (!ASSERT_EQ(args.retval, 0, buf))
> > - goto cleanup;
> > + args.prog_fd = bpf_program__fd(prog);
> > + err = bpf_prog_test_run_opts(attach_fd, &tattr);
> > + snprintf(buf, sizeof(buf), "attach_hid(%s)", prog_name);
> > + if (!ASSERT_EQ(args.retval, 0, buf))
> > + goto cleanup;
> > + } else {
> > + err = hid__load(hid_skel);
> > + if (!ASSERT_OK(err, "hid_skel_load"))
> > + goto cleanup;
> > + }
> >
> > hidraw_fd = open_hidraw(dev_id);
> > if (!ASSERT_GE(hidraw_fd, 0, "open_hidraw"))
> > @@ -447,6 +474,7 @@ static int prep_test(int dev_id, const char *prog_name, struct test_params *test
> >
> > test_data->skel = hid_skel;
> > test_data->hidraw_fd = hidraw_fd;
> > + test_data->hid_id = hid_id;
> >
> > return 0;
> >
> > @@ -693,6 +721,54 @@ static int test_hid_change_report(int uhid_fd, int dev_id)
> > return ret;
> > }
> >
> > +/*
> > + * Attach hid_user_raw_request to the given uhid device,
> > + * call the bpf program from userspace
> > + * check that the program is called and does the expected.
> > + */
> > +static int test_hid_user_raw_request_call(int uhid_fd, int dev_id)
> > +{
> > + struct test_params params;
> > + int err, prog_fd;
> > + int ret = -1;
> > + struct hid_hw_request_syscall_args args = {
> > + .retval = -1,
> > + .type = HID_FEATURE_REPORT,
> > + .request_type = HID_REQ_GET_REPORT,
> > + .size = 10,
> > + };
> > + DECLARE_LIBBPF_OPTS(bpf_test_run_opts, tattrs,
> > + .ctx_in = &args,
> > + .ctx_size_in = sizeof(args),
> > + );
> > +
> > + err = prep_test(dev_id, NULL, &params);
> > + if (!ASSERT_EQ(err, 0, "prep_test()"))
> > + goto cleanup;
> > +
> > + args.hid = params.hid_id;
> > + args.data[0] = 1; /* report ID */
> > +
> > + prog_fd = bpf_program__fd(params.skel->progs.hid_user_raw_request);
> > +
> > + err = bpf_prog_test_run_opts(prog_fd, &tattrs);
> > + if (!ASSERT_EQ(err, 0, "bpf_prog_test_run_opts"))
> > + goto cleanup;
> > +
> > + if (!ASSERT_EQ(args.retval, 2, "bpf_prog_test_run_opts_retval"))
> > + goto cleanup;
> > +
> > + if (!ASSERT_EQ(args.data[1], 2, "hid_user_raw_request_check_in"))
> > + goto cleanup;
> > +
> > + ret = 0;
> > +
> > +cleanup:
> > + cleanup_test(&params);
> > +
> > + return ret;
> > +}
> > +
> > void serial_test_hid_bpf(void)
> > {
> > int err, uhid_fd;
> > @@ -720,6 +796,8 @@ void serial_test_hid_bpf(void)
> > ASSERT_OK(err, "hid_attach_detach");
> > err = test_hid_change_report(uhid_fd, dev_id);
> > ASSERT_OK(err, "hid_change_report");
> > + err = test_hid_user_raw_request_call(uhid_fd, dev_id);
> > + ASSERT_OK(err, "hid_change_report");
> >
> > destroy(uhid_fd);
> >
> > diff --git a/tools/testing/selftests/bpf/progs/hid.c b/tools/testing/selftests/bpf/progs/hid.c
> > index ee7529c47ad8..e3444d444303 100644
> > --- a/tools/testing/selftests/bpf/progs/hid.c
> > +++ b/tools/testing/selftests/bpf/progs/hid.c
> > @@ -10,6 +10,13 @@ extern __u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx,
> > unsigned int offset,
> > const size_t __sz) __ksym;
> > extern int hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, u32 flags) __ksym;
> > +extern struct hid_bpf_ctx *hid_bpf_allocate_context(unsigned int hid_id) __ksym;
> > +extern void hid_bpf_release_context(struct hid_bpf_ctx *ctx) __ksym;
> > +extern int hid_bpf_hw_request(struct hid_bpf_ctx *ctx,
> > + __u8 *data,
> > + size_t len,
> > + enum hid_report_type type,
> > + int reqtype) __ksym;
> >
> > struct attach_prog_args {
> > int prog_fd;
> > @@ -56,3 +63,55 @@ int attach_prog(struct attach_prog_args *ctx)
> > 0);
> > return 0;
> > }
> > +
> > +struct hid_hw_request_syscall_args {
> > + /* data needs to come at offset 0 so we can do a memcpy into it */
> > + __u8 data[10];
> > + unsigned int hid;
> > + int retval;
> > + size_t size;
> > + enum hid_report_type type;
> > + __u8 request_type;
> > +};
> > +
> > +SEC("syscall")
> > +int hid_user_raw_request(struct hid_hw_request_syscall_args *args)
> > +{
> > + struct hid_bpf_ctx *ctx;
> > + int i, ret = 0;
> > + __u8 *data;
> > +
> > + ctx = hid_bpf_allocate_context(args->hid);
> > + if (!ctx)
> > + return 0; /* EPERM check */
> > +
> > + /* We can not use the context data memory directly in the hid_bpf call,
> > + * so we rely on the PTR_TO_MEM allocated in the hid_bpf_context
> > + */
> > + data = hid_bpf_get_data(ctx, 0 /* offset */, 10 /* size */);
> > + if (!data)
> > + goto out; /* EPERM check */
> > +
>
> If I'm reading this right, you need more than just returning PTR_TO_MEM. Since
> this points into allocated ctx, nothing prevents user from accessing data after
> we do hid_bpf_release_context.

oops. I missed that point.

TBH, ideally I wanted to directly pass args->data into
hid_bpf_hw_request(). But because args is seen as the context of the
program, I can not pass it to the kfunc arguments.
I would happily prevent getting a data pointer for a manually
allocated context if I could solve that issue. This would save me from
calling twice __builtin_memcpy.

That doesn't change the fact that you are correct and the PTR_TO_MEM
in kfunc code should be fixed.
But right now, I am not sure what you mean below and I'll need a
little bit more time to process it.

Cheers,
Benjamin

>
> The ref_obj_id of ctx needs to be transferred to R0.ref_obj_id, and R0.id needs
> to be assigned another id distinct from the ref_obj_id.
>
> My idea would be to give this type of function a new set, and handle this case
> of transferring ref_obj_id into R0. See is_ptr_cast_function in verifier.c.
> Shouldn't be too much code. You could even use the bpf_kfunc_arg_meta to store
> the ref_obj_id (and ensure only one referenced register exists among the 5
> arguments).
>
> > + __builtin_memcpy(data, args->data, sizeof(args->data));
> > +
> > + if (args->size <= sizeof(args->data)) {
> > + ret = hid_bpf_hw_request(ctx,
> > + data,
> > + args->size,
> > + args->type,
> > + args->request_type);
> > + args->retval = ret;
> > + if (ret < 0)
> > + goto out;
> > + } else {
> > + ret = -7; /* -E2BIG */
> > + goto out;
> > + }
> > +
> > + __builtin_memcpy(args->data, data, sizeof(args->data));
> > +
> > + out:
> > + hid_bpf_release_context(ctx);
> > +
> > + return ret;
> > +}
> > --
> > 2.36.1
> >
>
> --
> Kartikeya
>