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

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

On 5/19/22 14:51, Kumar Kartikeya Dwivedi wrote:
> On Thu, May 19, 2022 at 05:42:40PM IST, Benjamin Tissoires wrote:
>> 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.
> 
> Oh, is that why you need to do this? So if you were able to pass args->data, you
> wouldn't need this hid_bpf_get_data? kfunc does support taking PTR_TO_CTX (i.e.
> args in your case), I am not sure why you're not passing it in directly then.
> Did you encounter any errors when trying to do so? The only requirement is that
> args offset must be 0 (i.e. passed as is without increment).

With the following patch applied, the tests are failing:
---
diff --git a/tools/testing/selftests/bpf/progs/hid.c b/tools/testing/selftests/bpf/progs/hid.c
index 43724fd26fb9..976fc8b83934 100644
--- a/tools/testing/selftests/bpf/progs/hid.c
+++ b/tools/testing/selftests/bpf/progs/hid.c
@@ -80,24 +80,14 @@ 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 */
-
-       __builtin_memcpy(data, args->data, sizeof(args->data));
-
         if (args->size <= sizeof(args->data)) {
                 ret = hid_bpf_hw_request(ctx,
-                                        data,
+                                        args->data,
                                          args->size,
                                          args->type,
                                          args->request_type);
@@ -109,8 +99,6 @@ int hid_user_raw_request(struct hid_hw_request_syscall_args *args)
                 goto out;
         }
  
-       __builtin_memcpy(args->data, data, sizeof(args->data));
-
   out:
         hid_bpf_release_context(ctx);
  
---

Output of the verifier:

libbpf: prog 'hid_user_raw_request': BPF program load failed: Invalid argument
libbpf: prog 'hid_user_raw_request': -- BEGIN PROG LOAD LOG --
R1 type=ctx expected=fp
0: R1=ctx(off=0,imm=0) R10=fp0
; int hid_user_raw_request(struct hid_hw_request_syscall_args *args)
0: (bf) r7 = r1                       ; R1=ctx(off=0,imm=0) R7_w=ctx(off=0,imm=0)
; ctx = hid_bpf_allocate_context(args->hid);
1: (61) r1 = *(u32 *)(r7 +12)         ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff)) R7_w=ctx(off=0,imm=0)
; ctx = hid_bpf_allocate_context(args->hid);
2: (85) call hid_bpf_allocate_context#66484
3: (bf) r6 = r0                       ; R0_w=ptr_or_null_hid_bpf_ctx(id=2,ref_obj_id=2,off=0,imm=0) R6_w=ptr_or_null_hid_bpf_ctx(id=2,ref_obj_id=2,off=0,imm=0) refs=2
4: (b4) w8 = 0                        ; R8_w=0 refs=2
; if (!ctx)
5: (15) if r6 == 0x0 goto pc+12       ; R6_w=ptr_hid_bpf_ctx(ref_obj_id=2,off=0,imm=0) refs=2
6: (b4) w8 = -7                       ; R8_w=4294967289 refs=2
; if (args->size <= sizeof(args->data)) {
7: (79) r3 = *(u64 *)(r7 +24)         ; R3=scalar() R7=ctx(off=0,imm=0) refs=2
; if (args->size <= sizeof(args->data)) {
8: (25) if r3 > 0xa goto pc+7         ; R3=scalar(umax=10,var_off=(0x0; 0xf)) refs=2
; args->request_type);
9: (71) r5 = *(u8 *)(r7 +36)          ; R5_w=scalar(umax=255,var_off=(0x0; 0xff)) R7=ctx(off=0,imm=0) refs=2
; args->type,
10: (61) r4 = *(u32 *)(r7 +32)        ; R4_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff)) R7=ctx(off=0,imm=0) refs=2
; ret = hid_bpf_hw_request(ctx,
11: (bf) r1 = r6                      ; R1_w=ptr_hid_bpf_ctx(ref_obj_id=2,off=0,imm=0) R6=ptr_hid_bpf_ctx(ref_obj_id=2,off=0,imm=0) refs=2
12: (bf) r2 = r7                      ; R2_w=ctx(off=0,imm=0) R7=ctx(off=0,imm=0) refs=2
13: (85) call hid_bpf_hw_request#66480
R2 type=ctx expected=fp
processed 14 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 1
-- END PROG LOAD LOG --

Maybe I am wrongly declaring hid_bpf_hw_request()?

Cheers,
Benjamin

> 
>>
>> 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
>>>
>>
> 
> --
> Kartikeya
>