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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>
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