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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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.