Re: [PATCH 3/5] x86/vsyscall: Add vsyscall emulation for #GP

[H. Peter Anvin]

On March 4, 2026 5:45:48 PM PST, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>On 3/4/26 16:10, Sohil Mehta wrote:
>> Vsyscall emulation has two modes of operation, specified by the
>> vsyscall={xonly, emulate} kernel command line option. The vsyscall page
>> is marked as execute-only in XONLY mode or read-execute in EMULATE mode.
>
>Is it really "marked as execute only"? We don't have a real execute-only
>paging permission on x86, the closest we've got is memory marked with a
>pkey that's got the AccessDisable bit set.
>
>I think it's _called_ execute-only because the kernel makes it behave
>like execute-only memory when it's handling the page fault. But I dobn't
>think it is super accurate to say it is "marked" as execute-only.
>
>The rest of it looks great to me, though.

It's not marked as anything; it is in fact not present.