Re: [RFC] selftests/x86: Add test_vsyscall

From: Andy Lutomirski
Date: Fri Jan 05 2018 - 15:10:10 EST



> On Jan 5, 2018, at 11:28 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
>
>> On Fri, Jan 05, 2018 at 11:22:21AM -0800, Andy Lutomirski wrote:
>> It's emulated! We catch the page fault and fake the whole thing :)
>
> Then I'm really confused. It says "ro" above, which means _PAGE_RW is
> not set so page is read-only.
>
> I must be missing something...
>

It's meant to be read-only, user-acccessible, NX as far as the CPU is concerned. When user code calls it, we get an instruction fetch fault, and the kernel fixes it up.

> --
> Regards/Gruss,
> Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.