Date:   Thu, 19 May 2022 14:12:40 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Joe Stringer <joe@...ium.io>, Jonathan Corbet <corbet@....net>,
        Tero Kristo <tero.kristo@...ux.intel.com>,
        lkml <linux-kernel@...r.kernel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 12/17] selftests/bpf: add tests for bpf_hid_hw_request

On Thu, May 19, 2022 at 12:20 AM Kumar Kartikeya Dwivedi
<memxor@...il.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@...hat.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
>

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