selftest/bpf: Test the read of vsyscall page under x86-64

Under x86-64, when using bpf_probe_read_kernel{_str}() or
bpf_probe_read{_str}() to read vsyscall page, the read may trigger oops,
so add one test case to ensure that the problem is fixed. Beside those
four bpf helpers mentioned above, testing the read of vsyscall page by
using bpf_probe_read_user{_str} and bpf_copy_from_user{_task}() as well.

The test case passes the address of vsyscall page to these six helpers
and checks whether the returned values are expected:

1) For bpf_probe_read_kernel{_str}()/bpf_probe_read{_str}(), the
   expected return value is -ERANGE as shown below:

bpf_probe_read_kernel_common
  copy_from_kernel_nofault
    // false, return -ERANGE
    copy_from_kernel_nofault_allowed

2) For bpf_probe_read_user{_str}(), the expected return value is -EFAULT
   as show below:

bpf_probe_read_user_common
  copy_from_user_nofault
    // false, return -EFAULT
    __access_ok

3) For bpf_copy_from_user(), the expected return value is -EFAULT:

// return -EFAULT
bpf_copy_from_user
  copy_from_user
    _copy_from_user
      // return false
      access_ok

4) For bpf_copy_from_user_task(), the expected return value is -EFAULT:

// return -EFAULT
bpf_copy_from_user_task
  access_process_vm
    // return 0
    vma_lookup()
    // return 0
    expand_stack()

The occurrence of oops depends on the availability of CPU SMAP [1]
feature and there are three possible configurations of vsyscall page in
the boot cmd-line: vsyscall={xonly|none|emulate}, so there are a total
of six possible combinations. Under all these combinations, the test
case runs successfully.

[1]: https://en.wikipedia.org/wiki/Supervisor_Mode_Access_Prevention



Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20240202103935.3154011-4-houtao@huaweicloud.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>