[bpf-next,v11,4/7] selftests/bpf: add test for accessing ctx from syscall program type

We need to also export the kfunc set to the syscall program type,
and then add a couple of eBPF programs that are testing those calls.

The first one checks for valid access, and the second one is OK
from a static analysis point of view but fails at run time because
we are trying to access outside of the allocated memory.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

changes in v11:
- use new way of declaring tests

changes in v10:
- use new definitions for tests in an array
- add a new kfunc syscall_test_null_fail test

no changes in v9

no changes in v8

changes in v7:
- add 1 more case to ensure we can read the entire sizeof(ctx)
- add a test case for when the context is NULL

new in v6
---
 net/bpf/test_run.c                            |   1 +
 .../selftests/bpf/prog_tests/kfunc_call.c     | 143 +++++++++++++++++-
 .../selftests/bpf/progs/kfunc_call_fail.c     |  39 +++++
 .../selftests/bpf/progs/kfunc_call_test.c     |  38 +++++
 4 files changed, 214 insertions(+), 7 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/kfunc_call_fail.c

On Wed, Sep 7, 2022 at 10:46 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Tue, 6 Sept 2022 at 17:13, Benjamin Tissoires
> <benjamin.tissoires@redhat.com> wrote:
> >
> > We need to also export the kfunc set to the syscall program type,
> > and then add a couple of eBPF programs that are testing those calls.
> >
> > The first one checks for valid access, and the second one is OK
> > from a static analysis point of view but fails at run time because
> > we are trying to access outside of the allocated memory.
> >
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> >
> > ---
>
> CI is failing for test_progs-no_alu32:
> https://github.com/kernel-patches/bpf/runs/8220916615?check_suite_focus=true
>
> >
> > changes in v11:
> > - use new way of declaring tests
> >
> > changes in v10:
> > - use new definitions for tests in an array
> > - add a new kfunc syscall_test_null_fail test
> >
> > no changes in v9
> >
> > no changes in v8
> >
> > changes in v7:
> > - add 1 more case to ensure we can read the entire sizeof(ctx)
> > - add a test case for when the context is NULL
> >
> > new in v6
> > ---
> >  net/bpf/test_run.c                            |   1 +
> >  .../selftests/bpf/prog_tests/kfunc_call.c     | 143 +++++++++++++++++-
> >  .../selftests/bpf/progs/kfunc_call_fail.c     |  39 +++++
> >  .../selftests/bpf/progs/kfunc_call_test.c     |  38 +++++
> >  4 files changed, 214 insertions(+), 7 deletions(-)
> >  create mode 100644 tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> >
> > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> > index 25d8ecf105aa..f16baf977a21 100644
> > --- a/net/bpf/test_run.c
> > +++ b/net/bpf/test_run.c
> > @@ -1634,6 +1634,7 @@ static int __init bpf_prog_test_run_init(void)
> >
> >         ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_prog_test_kfunc_set);
> >         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_prog_test_kfunc_set);
> > +       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_prog_test_kfunc_set);
> >         return ret ?: register_btf_id_dtor_kfuncs(bpf_prog_test_dtor_kfunc,
> >                                                   ARRAY_SIZE(bpf_prog_test_dtor_kfunc),
> >                                                   THIS_MODULE);
> > diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > index 9dfbe5355a2d..d5881c3331a8 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > @@ -2,6 +2,7 @@
> >  /* Copyright (c) 2021 Facebook */
> >  #include <test_progs.h>
> >  #include <network_helpers.h>
> > +#include "kfunc_call_fail.skel.h"
> >  #include "kfunc_call_test.skel.h"
> >  #include "kfunc_call_test.lskel.h"
> >  #include "kfunc_call_test_subprog.skel.h"
> > @@ -10,37 +11,96 @@
> >
> >  #include "cap_helpers.h"
> >
> > +static size_t log_buf_sz = 1048576; /* 1 MB */
> > +static char obj_log_buf[1048576];
> > +
> > +enum kfunc_test_type {
> > +       tc_test = 0,
> > +       syscall_test,
> > +       syscall_null_ctx_test,
> > +};
> > +
> >  struct kfunc_test_params {
> >         const char *prog_name;
> >         unsigned long lskel_prog_desc_offset;
> >         int retval;
> > +       enum kfunc_test_type test_type;
> > +       const char *expected_err_msg;
> >  };
> >
> > -#define TC_TEST(name, __retval) \
> > +#define __BPF_TEST_SUCCESS(name, __retval, type) \
> >         { \
> >           .prog_name = #name, \
> >           .lskel_prog_desc_offset = offsetof(struct kfunc_call_test_lskel, progs.name), \
> >           .retval = __retval, \
> > +         .test_type = type, \
> > +         .expected_err_msg = NULL, \
> > +       }
> > +
> > +#define __BPF_TEST_FAIL(name, __retval, type, error_msg) \
> > +       { \
> > +         .prog_name = #name, \
> > +         .lskel_prog_desc_offset = 0 /* unused when test is failing */, \
> > +         .retval = __retval, \
> > +         .test_type = type, \
> > +         .expected_err_msg = error_msg, \
> >         }
> >
> > +#define TC_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, tc_test)
> > +#define SYSCALL_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, syscall_test)
> > +#define SYSCALL_NULL_CTX_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, syscall_null_ctx_test)
> > +
> > +#define SYSCALL_NULL_CTX_FAIL(name, retval, error_msg) \
> > +       __BPF_TEST_FAIL(name, retval, syscall_null_ctx_test, error_msg)
> > +
> >  static struct kfunc_test_params kfunc_tests[] = {
> > +       /* failure cases:
> > +        * if retval is 0 -> the program will fail to load and the error message is an error
> > +        * if retval is not 0 -> the program can be loaded but running it will gives the
> > +        *                       provided return value. The error message is thus the one
> > +        *                       from a successful load
> > +        */
> > +       SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_fail, -EINVAL, "processed 4 insns"),
> > +       SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_null_fail, -EINVAL, "processed 4 insns"),
> > +
> > +       /* success cases */
> >         TC_TEST(kfunc_call_test1, 12),
> >         TC_TEST(kfunc_call_test2, 3),
> >         TC_TEST(kfunc_call_test_ref_btf_id, 0),
> > +       SYSCALL_TEST(kfunc_syscall_test, 0),
> > +       SYSCALL_NULL_CTX_TEST(kfunc_syscall_test_null, 0),
> > +};
> > +
> > +struct syscall_test_args {
> > +       __u8 data[16];
> > +       size_t size;
> >  };
> >
> >  static void verify_success(struct kfunc_test_params *param)
> >  {
> >         struct kfunc_call_test_lskel *lskel = NULL;
> > +       LIBBPF_OPTS(bpf_test_run_opts, topts);
> >         struct bpf_prog_desc *lskel_prog;
> >         struct kfunc_call_test *skel;
> >         struct bpf_program *prog;
> >         int prog_fd, err;
> > -       LIBBPF_OPTS(bpf_test_run_opts, topts,
> > -               .data_in = &pkt_v4,
> > -               .data_size_in = sizeof(pkt_v4),
> > -               .repeat = 1,
> > -       );
> > +       struct syscall_test_args args = {
> > +               .size = 10,
> > +       };
> > +
> > +       switch (param->test_type) {
> > +       case syscall_test:
> > +               topts.ctx_in = &args;
> > +               topts.ctx_size_in = sizeof(args);
> > +               /* fallthrough */
> > +       case syscall_null_ctx_test:
> > +               break;
> > +       case tc_test:
> > +               topts.data_in = &pkt_v4;
> > +               topts.data_size_in = sizeof(pkt_v4);
> > +               topts.repeat = 1;
> > +               break;
> > +       }
> >
> >         /* first test with normal libbpf */
> >         skel = kfunc_call_test__open_and_load();
> > @@ -79,6 +139,72 @@ static void verify_success(struct kfunc_test_params *param)
> >                 kfunc_call_test_lskel__destroy(lskel);
> >  }
> >
> > +static void verify_fail(struct kfunc_test_params *param)
> > +{
> > +       LIBBPF_OPTS(bpf_object_open_opts, opts);
> > +       LIBBPF_OPTS(bpf_test_run_opts, topts);
> > +       struct bpf_program *prog;
> > +       struct kfunc_call_fail *skel;
> > +       int prog_fd, err;
> > +       struct syscall_test_args args = {
> > +               .size = 10,
> > +       };
> > +
> > +       opts.kernel_log_buf = obj_log_buf;
> > +       opts.kernel_log_size = log_buf_sz;
> > +       opts.kernel_log_level = 1;
> > +
> > +       switch (param->test_type) {
> > +       case syscall_test:
> > +               topts.ctx_in = &args;
> > +               topts.ctx_size_in = sizeof(args);
> > +               /* fallthrough */
> > +       case syscall_null_ctx_test:
> > +               break;
> > +       case tc_test:
> > +               topts.data_in = &pkt_v4;
> > +               topts.data_size_in = sizeof(pkt_v4);
> > +               break;
> > +               topts.repeat = 1;
> > +       }
> > +
> > +       skel = kfunc_call_fail__open_opts(&opts);
> > +       if (!ASSERT_OK_PTR(skel, "kfunc_call_fail__open_opts"))
> > +               goto cleanup;
> > +
> > +       prog = bpf_object__find_program_by_name(skel->obj, param->prog_name);
> > +       if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
> > +               goto cleanup;
> > +
> > +       bpf_program__set_autoload(prog, true);
> > +
> > +       err = kfunc_call_fail__load(skel);
> > +       if (!param->retval) {
> > +               /* the verifier is supposed to complain and refuses to load */
> > +               if (!ASSERT_ERR(err, "unexpected load success"))
> > +                       goto out_err;
> > +
> > +       } else {
> > +               /* the program is loaded but must dynamically fail */
> > +               if (!ASSERT_OK(err, "unexpected load error"))
> > +                       goto out_err;
> > +
> > +               prog_fd = bpf_program__fd(prog);
> > +               err = bpf_prog_test_run_opts(prog_fd, &topts);
> > +               if (!ASSERT_EQ(err, param->retval, param->prog_name))
> > +                       goto out_err;
> > +       }
> > +
> > +out_err:
> > +       if (!ASSERT_OK_PTR(strstr(obj_log_buf, param->expected_err_msg), "expected_err_msg")) {
> > +               fprintf(stderr, "Expected err_msg: %s\n", param->expected_err_msg);
> > +               fprintf(stderr, "Verifier output: %s\n", obj_log_buf);
> > +       }
> > +
> > +cleanup:
> > +       kfunc_call_fail__destroy(skel);
> > +}
> > +
> >  static void test_main(void)
> >  {
> >         int i;
> > @@ -87,7 +213,10 @@ static void test_main(void)
> >                 if (!test__start_subtest(kfunc_tests[i].prog_name))
> >                         continue;
> >
> > -               verify_success(&kfunc_tests[i]);
> > +               if (!kfunc_tests[i].expected_err_msg)
> > +                       verify_success(&kfunc_tests[i]);
> > +               else
> > +                       verify_fail(&kfunc_tests[i]);
> >         }
> >  }
> >
> > diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_fail.c b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > new file mode 100644
> > index 000000000000..4168027f2ab1
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > @@ -0,0 +1,39 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2021 Facebook */
> > +#include <vmlinux.h>
> > +#include <bpf/bpf_helpers.h>
> > +
> > +extern void bpf_kfunc_call_test_mem_len_pass1(void *mem, int len) __ksym;
> > +
> > +struct syscall_test_args {
> > +       __u8 data[16];
> > +       size_t size;
> > +};
> > +
> > +SEC("?syscall")
> > +int kfunc_syscall_test_fail(struct syscall_test_args *args)
> > +{
> > +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args) + 1);
> > +
> > +       return 0;
> > +}
> > +
> > +SEC("?syscall")
> > +int kfunc_syscall_test_null_fail(struct syscall_test_args *args)
> > +{
> > +       /* Must be called with args as a NULL pointer
> > +        * we do not check for it to have the verifier consider that
> > +        * the pointer might not be null, and so we can load it.
> > +        *
> > +        * So the following can not be added:
> > +        *
> > +        * if (args)
> > +        *      return -22;
> > +        */
> > +
> > +       bpf_kfunc_call_test_mem_len_pass1(args, sizeof(*args));
> > +
> > +       return 0;
> > +}
> > +
> > +char _license[] SEC("license") = "GPL";
> > diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_test.c b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > index 5aecbb9fdc68..94c05267e5e7 100644
> > --- a/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > +++ b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > @@ -92,4 +92,42 @@ int kfunc_call_test_pass(struct __sk_buff *skb)
> >         return 0;
> >  }
> >
> > +struct syscall_test_args {
> > +       __u8 data[16];
> > +       size_t size;
> > +};
> > +
> > +SEC("syscall")
> > +int kfunc_syscall_test(struct syscall_test_args *args)
> > +{
> > +       const int size = args->size;
> > +
> > +       if (size > sizeof(args->data))
> > +               return -7; /* -E2BIG */
> > +
>
> Looks like it is due to this. Verifier is confused because:
> r7 = args->data;
> r1 = r7;
>
> then it does r1 <<= 32; r1 >>=32; clearing upper 32 bits, so both r1
> and r7 lose the id association which propagates the bounds of r1
> learnt from comparison of it with sizeof(args->data);
>
> > +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(args->data));
> > +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args));
>
> Later llvm assigns r7 to r2 for this call's 2nd arg. At this point the
> verifier still thinks r7 is unbounded, while to make a call with mem,
> len pair you need non-negative min value.
>
> Easiest way might be to just do args->size & sizeof(args->data), as
> the verifier log says. You might still keep the error above.
> Others may have better ideas/insights.

I just did s/const int size/const long size/
to fix the issues.

Also fixed commit in patch 3 that talks about max_ctx_offset
and did:
-       BTF_KFUNC_SET_MAX_CNT = 64,
+       BTF_KFUNC_SET_MAX_CNT = 256,

and applied.

On Wed, Sep 7, 2022 at 8:09 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Sep 7, 2022 at 10:46 AM Kumar Kartikeya Dwivedi
> <memxor@gmail.com> wrote:
> >
> > On Tue, 6 Sept 2022 at 17:13, Benjamin Tissoires
> > <benjamin.tissoires@redhat.com> wrote:
> > >
> > > We need to also export the kfunc set to the syscall program type,
> > > and then add a couple of eBPF programs that are testing those calls.
> > >
> > > The first one checks for valid access, and the second one is OK
> > > from a static analysis point of view but fails at run time because
> > > we are trying to access outside of the allocated memory.
> > >
> > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> > >
> > > ---
> >
> > CI is failing for test_progs-no_alu32:
> > https://github.com/kernel-patches/bpf/runs/8220916615?check_suite_focus=true
> >
> > >
> > > changes in v11:
> > > - use new way of declaring tests
> > >
> > > changes in v10:
> > > - use new definitions for tests in an array
> > > - add a new kfunc syscall_test_null_fail test
> > >
> > > no changes in v9
> > >
> > > no changes in v8
> > >
> > > changes in v7:
> > > - add 1 more case to ensure we can read the entire sizeof(ctx)
> > > - add a test case for when the context is NULL
> > >
> > > new in v6
> > > ---
> > >  net/bpf/test_run.c                            |   1 +
> > >  .../selftests/bpf/prog_tests/kfunc_call.c     | 143 +++++++++++++++++-
> > >  .../selftests/bpf/progs/kfunc_call_fail.c     |  39 +++++
> > >  .../selftests/bpf/progs/kfunc_call_test.c     |  38 +++++
> > >  4 files changed, 214 insertions(+), 7 deletions(-)
> > >  create mode 100644 tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > >
> > > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> > > index 25d8ecf105aa..f16baf977a21 100644
> > > --- a/net/bpf/test_run.c
> > > +++ b/net/bpf/test_run.c
> > > @@ -1634,6 +1634,7 @@ static int __init bpf_prog_test_run_init(void)
> > >
> > >         ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_prog_test_kfunc_set);
> > >         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_prog_test_kfunc_set);
> > > +       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_prog_test_kfunc_set);
> > >         return ret ?: register_btf_id_dtor_kfuncs(bpf_prog_test_dtor_kfunc,
> > >                                                   ARRAY_SIZE(bpf_prog_test_dtor_kfunc),
> > >                                                   THIS_MODULE);
> > > diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > > index 9dfbe5355a2d..d5881c3331a8 100644
> > > --- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > > +++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > > @@ -2,6 +2,7 @@
> > >  /* Copyright (c) 2021 Facebook */
> > >  #include <test_progs.h>
> > >  #include <network_helpers.h>
> > > +#include "kfunc_call_fail.skel.h"
> > >  #include "kfunc_call_test.skel.h"
> > >  #include "kfunc_call_test.lskel.h"
> > >  #include "kfunc_call_test_subprog.skel.h"
> > > @@ -10,37 +11,96 @@
> > >
> > >  #include "cap_helpers.h"
> > >
> > > +static size_t log_buf_sz = 1048576; /* 1 MB */
> > > +static char obj_log_buf[1048576];
> > > +
> > > +enum kfunc_test_type {
> > > +       tc_test = 0,
> > > +       syscall_test,
> > > +       syscall_null_ctx_test,
> > > +};
> > > +
> > >  struct kfunc_test_params {
> > >         const char *prog_name;
> > >         unsigned long lskel_prog_desc_offset;
> > >         int retval;
> > > +       enum kfunc_test_type test_type;
> > > +       const char *expected_err_msg;
> > >  };
> > >
> > > -#define TC_TEST(name, __retval) \
> > > +#define __BPF_TEST_SUCCESS(name, __retval, type) \
> > >         { \
> > >           .prog_name = #name, \
> > >           .lskel_prog_desc_offset = offsetof(struct kfunc_call_test_lskel, progs.name), \
> > >           .retval = __retval, \
> > > +         .test_type = type, \
> > > +         .expected_err_msg = NULL, \
> > > +       }
> > > +
> > > +#define __BPF_TEST_FAIL(name, __retval, type, error_msg) \
> > > +       { \
> > > +         .prog_name = #name, \
> > > +         .lskel_prog_desc_offset = 0 /* unused when test is failing */, \
> > > +         .retval = __retval, \
> > > +         .test_type = type, \
> > > +         .expected_err_msg = error_msg, \
> > >         }
> > >
> > > +#define TC_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, tc_test)
> > > +#define SYSCALL_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, syscall_test)
> > > +#define SYSCALL_NULL_CTX_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, syscall_null_ctx_test)
> > > +
> > > +#define SYSCALL_NULL_CTX_FAIL(name, retval, error_msg) \
> > > +       __BPF_TEST_FAIL(name, retval, syscall_null_ctx_test, error_msg)
> > > +
> > >  static struct kfunc_test_params kfunc_tests[] = {
> > > +       /* failure cases:
> > > +        * if retval is 0 -> the program will fail to load and the error message is an error
> > > +        * if retval is not 0 -> the program can be loaded but running it will gives the
> > > +        *                       provided return value. The error message is thus the one
> > > +        *                       from a successful load
> > > +        */
> > > +       SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_fail, -EINVAL, "processed 4 insns"),
> > > +       SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_null_fail, -EINVAL, "processed 4 insns"),
> > > +
> > > +       /* success cases */
> > >         TC_TEST(kfunc_call_test1, 12),
> > >         TC_TEST(kfunc_call_test2, 3),
> > >         TC_TEST(kfunc_call_test_ref_btf_id, 0),
> > > +       SYSCALL_TEST(kfunc_syscall_test, 0),
> > > +       SYSCALL_NULL_CTX_TEST(kfunc_syscall_test_null, 0),
> > > +};
> > > +
> > > +struct syscall_test_args {
> > > +       __u8 data[16];
> > > +       size_t size;
> > >  };
> > >
> > >  static void verify_success(struct kfunc_test_params *param)
> > >  {
> > >         struct kfunc_call_test_lskel *lskel = NULL;
> > > +       LIBBPF_OPTS(bpf_test_run_opts, topts);
> > >         struct bpf_prog_desc *lskel_prog;
> > >         struct kfunc_call_test *skel;
> > >         struct bpf_program *prog;
> > >         int prog_fd, err;
> > > -       LIBBPF_OPTS(bpf_test_run_opts, topts,
> > > -               .data_in = &pkt_v4,
> > > -               .data_size_in = sizeof(pkt_v4),
> > > -               .repeat = 1,
> > > -       );
> > > +       struct syscall_test_args args = {
> > > +               .size = 10,
> > > +       };
> > > +
> > > +       switch (param->test_type) {
> > > +       case syscall_test:
> > > +               topts.ctx_in = &args;
> > > +               topts.ctx_size_in = sizeof(args);
> > > +               /* fallthrough */
> > > +       case syscall_null_ctx_test:
> > > +               break;
> > > +       case tc_test:
> > > +               topts.data_in = &pkt_v4;
> > > +               topts.data_size_in = sizeof(pkt_v4);
> > > +               topts.repeat = 1;
> > > +               break;
> > > +       }
> > >
> > >         /* first test with normal libbpf */
> > >         skel = kfunc_call_test__open_and_load();
> > > @@ -79,6 +139,72 @@ static void verify_success(struct kfunc_test_params *param)
> > >                 kfunc_call_test_lskel__destroy(lskel);
> > >  }
> > >
> > > +static void verify_fail(struct kfunc_test_params *param)
> > > +{
> > > +       LIBBPF_OPTS(bpf_object_open_opts, opts);
> > > +       LIBBPF_OPTS(bpf_test_run_opts, topts);
> > > +       struct bpf_program *prog;
> > > +       struct kfunc_call_fail *skel;
> > > +       int prog_fd, err;
> > > +       struct syscall_test_args args = {
> > > +               .size = 10,
> > > +       };
> > > +
> > > +       opts.kernel_log_buf = obj_log_buf;
> > > +       opts.kernel_log_size = log_buf_sz;
> > > +       opts.kernel_log_level = 1;
> > > +
> > > +       switch (param->test_type) {
> > > +       case syscall_test:
> > > +               topts.ctx_in = &args;
> > > +               topts.ctx_size_in = sizeof(args);
> > > +               /* fallthrough */
> > > +       case syscall_null_ctx_test:
> > > +               break;
> > > +       case tc_test:
> > > +               topts.data_in = &pkt_v4;
> > > +               topts.data_size_in = sizeof(pkt_v4);
> > > +               break;
> > > +               topts.repeat = 1;
> > > +       }
> > > +
> > > +       skel = kfunc_call_fail__open_opts(&opts);
> > > +       if (!ASSERT_OK_PTR(skel, "kfunc_call_fail__open_opts"))
> > > +               goto cleanup;
> > > +
> > > +       prog = bpf_object__find_program_by_name(skel->obj, param->prog_name);
> > > +       if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
> > > +               goto cleanup;
> > > +
> > > +       bpf_program__set_autoload(prog, true);
> > > +
> > > +       err = kfunc_call_fail__load(skel);
> > > +       if (!param->retval) {
> > > +               /* the verifier is supposed to complain and refuses to load */
> > > +               if (!ASSERT_ERR(err, "unexpected load success"))
> > > +                       goto out_err;
> > > +
> > > +       } else {
> > > +               /* the program is loaded but must dynamically fail */
> > > +               if (!ASSERT_OK(err, "unexpected load error"))
> > > +                       goto out_err;
> > > +
> > > +               prog_fd = bpf_program__fd(prog);
> > > +               err = bpf_prog_test_run_opts(prog_fd, &topts);
> > > +               if (!ASSERT_EQ(err, param->retval, param->prog_name))
> > > +                       goto out_err;
> > > +       }
> > > +
> > > +out_err:
> > > +       if (!ASSERT_OK_PTR(strstr(obj_log_buf, param->expected_err_msg), "expected_err_msg")) {
> > > +               fprintf(stderr, "Expected err_msg: %s\n", param->expected_err_msg);
> > > +               fprintf(stderr, "Verifier output: %s\n", obj_log_buf);
> > > +       }
> > > +
> > > +cleanup:
> > > +       kfunc_call_fail__destroy(skel);
> > > +}
> > > +
> > >  static void test_main(void)
> > >  {
> > >         int i;
> > > @@ -87,7 +213,10 @@ static void test_main(void)
> > >                 if (!test__start_subtest(kfunc_tests[i].prog_name))
> > >                         continue;
> > >
> > > -               verify_success(&kfunc_tests[i]);
> > > +               if (!kfunc_tests[i].expected_err_msg)
> > > +                       verify_success(&kfunc_tests[i]);
> > > +               else
> > > +                       verify_fail(&kfunc_tests[i]);
> > >         }
> > >  }
> > >
> > > diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_fail.c b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > > new file mode 100644
> > > index 000000000000..4168027f2ab1
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > > @@ -0,0 +1,39 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/* Copyright (c) 2021 Facebook */
> > > +#include <vmlinux.h>
> > > +#include <bpf/bpf_helpers.h>
> > > +
> > > +extern void bpf_kfunc_call_test_mem_len_pass1(void *mem, int len) __ksym;
> > > +
> > > +struct syscall_test_args {
> > > +       __u8 data[16];
> > > +       size_t size;
> > > +};
> > > +
> > > +SEC("?syscall")
> > > +int kfunc_syscall_test_fail(struct syscall_test_args *args)
> > > +{
> > > +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args) + 1);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +SEC("?syscall")
> > > +int kfunc_syscall_test_null_fail(struct syscall_test_args *args)
> > > +{
> > > +       /* Must be called with args as a NULL pointer
> > > +        * we do not check for it to have the verifier consider that
> > > +        * the pointer might not be null, and so we can load it.
> > > +        *
> > > +        * So the following can not be added:
> > > +        *
> > > +        * if (args)
> > > +        *      return -22;
> > > +        */
> > > +
> > > +       bpf_kfunc_call_test_mem_len_pass1(args, sizeof(*args));
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +char _license[] SEC("license") = "GPL";
> > > diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_test.c b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > > index 5aecbb9fdc68..94c05267e5e7 100644
> > > --- a/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > > +++ b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > > @@ -92,4 +92,42 @@ int kfunc_call_test_pass(struct __sk_buff *skb)
> > >         return 0;
> > >  }
> > >
> > > +struct syscall_test_args {
> > > +       __u8 data[16];
> > > +       size_t size;
> > > +};
> > > +
> > > +SEC("syscall")
> > > +int kfunc_syscall_test(struct syscall_test_args *args)
> > > +{
> > > +       const int size = args->size;
> > > +
> > > +       if (size > sizeof(args->data))
> > > +               return -7; /* -E2BIG */
> > > +
> >
> > Looks like it is due to this. Verifier is confused because:
> > r7 = args->data;
> > r1 = r7;
> >
> > then it does r1 <<= 32; r1 >>=32; clearing upper 32 bits, so both r1
> > and r7 lose the id association which propagates the bounds of r1
> > learnt from comparison of it with sizeof(args->data);
> >
> > > +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(args->data));
> > > +       bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args));
> >
> > Later llvm assigns r7 to r2 for this call's 2nd arg. At this point the
> > verifier still thinks r7 is unbounded, while to make a call with mem,
> > len pair you need non-negative min value.
> >
> > Easiest way might be to just do args->size & sizeof(args->data), as
> > the verifier log says. You might still keep the error above.
> > Others may have better ideas/insights.
>
> I just did s/const int size/const long size/
> to fix the issues.
>
> Also fixed commit in patch 3 that talks about max_ctx_offset
> and did:
> -       BTF_KFUNC_SET_MAX_CNT = 64,
> +       BTF_KFUNC_SET_MAX_CNT = 256,
>
> and applied.
>

Great!

Many thanks to both of you for your time and getting me there :)

Cheers,
Benjamin