Hi,
On 2/8/2022 2:33 AM, Yonghong Song wrote:
>
>
> On 2/5/22 8:31 PM, Hou Tao wrote:
>> In add_kfunc_call(), bpf_kfunc_desc->imm with type s32 is used to
>> represent the offset of called kfunc from __bpf_call_base, so
>> add a test to ensure that the offset will not be overflowed.
>>
>> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
>> ---
>> .../selftests/bpf/prog_tests/ksyms_module.c | 42 +++++++++++++++++++
>> 1 file changed, 42 insertions(+)
>>
[...]
>> + /* Ensure kfunc call is supported */
>> + skel = test_ksyms_module__open_and_load();
>> + if (!ASSERT_OK_PTR(skel, "test_ksyms_module__open"))
>> + return;
>> +
>> + err = kallsyms_find("bpf_testmod_test_mod_kfunc", &kfunc_addr);
>> + if (!ASSERT_OK(err, "find kfunc addr"))
>> + goto cleanup;
>> +
>> + err = kallsyms_find("__bpf_call_base", &base_addr);
>> + if (!ASSERT_OK(err, "find base addr"))
>> + goto cleanup;
>> +
>> + used_offset = kfunc_addr - base_addr;
>> + actual_offset = kfunc_addr - base_addr;
>> + ASSERT_EQ((long long)used_offset, actual_offset, "kfunc offset
>> overflowed");
>
> I am a little bit confused about motivation here. Maybe I missed something. If
> we indeed have kfunc offset overflow,
> should kernel verifier just reject the program? Specially,
> we should make the above test_ksyms_module__open_and_load()
> fail?
In add_kfunc_call(), the calculation of imm doesn't consider the overflow
of s32. So test_ksyms_module__open_and_load() will succeed. I think the
better solution is to put the overflow check in add_kfunc_call(), so will
drop this patch and add the overflow check in add_kfunc_call() instead.
Regards,
Tao
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