Re: [PATCH 24/30] x86, kaiser: disable native VSYSCALL

[Andy Lutomirski]

On Thu, Nov 9, 2017 at 10:31 PM, Dave Hansen
<dave.hansen@xxxxxxxxxxxxxxx> wrote:
> On 11/09/2017 06:25 PM, Andy Lutomirski wrote:
>> Here are two proposals to address this without breaking vsyscalls.
>>
>> 1. Set NX on low mappings that are _PAGE_USER.  Don't set NX on high
>> mappings but, optionally, warn if you see _PAGE_USER on any address
>> that isn't the vsyscall page.
>>
>> 2. Ignore _PAGE_USER entirely and just mark the EFI mm as special so
>> KAISER doesn't muck with it.
>
> These are totally doable.  But, what's the big deal with breaking native
> vsyscall?  We can still do the emulation so nothing breaks: it is just slow.

I have nothing against disabling native.  I object to breaking the
weird binary tracing behavior in the emulation mode, especially if
it's tangled up with KAISER.  I got all kinds of flak in an earlier
version of the vsyscall emulation patches when I broke that use case.
KAISER may get very widely backported -- let's not make changes that
are already known to break things.