[musl] Re: [PATCH v2] x86: Implement arch_prctl(ARCH_VSYSCALL_CONTROL) to disable vsyscall

[Florian Weimer <fweimer@redhat.com>]

* Andrei Vagin:

>> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
>> index fd2ee9408e91..8eb3bcf2cedf 100644
>> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
>> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
>> @@ -174,6 +174,12 @@ bool emulate_vsyscall(unsigned long error_code,
>>
>>         tsk = current;
>>
>> +       if (tsk->mm->context.vsyscall_disabled) {
>> +               warn_bad_vsyscall(KERN_WARNING, regs,
>> +                                 "vsyscall after lockout (exploit attempt?)");
>
> I don't think that we need this warning message. If we disable
> vsyscall, its address range is not differ from other addresses around
> and has to be handled the same way. For example, gVisor or any other
> sandbox engines may want to emulate vsyscall, but the kernel log will
> be full of such messages.

But with vsyscall=none, such messages are already printed.  That's why I
added the warning for the lockout case as well.

>> diff --git a/tools/testing/selftests/x86/vsyscall_control.c b/tools/testing/selftests/x86/vsyscall_control.c
>> new file mode 100644
>> index 000000000000..ee966f936c89
>> --- /dev/null
>> +++ b/tools/testing/selftests/x86/vsyscall_control.c
>
> I would move the test in a separate patch...

I can do that if it simplifies matters.

Thanks,
Florian