Re: [PATCH v3 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule

[Andrew Lutomirski]

On Tuesday, May 31, 2011, Ingo Molnar <mingo@xxxxxxx> wrote:
>
> * Ingo Molnar <mingo@xxxxxxx> wrote:
>
>> [...] solution that filters the caller RIP at the generic syscall
>> entry point and checks RCX against the 'expected' SYSCALL
>> instruction address, which is the (per task) vdso-address +
>> constant-offset.
>
> Note that this solution would allow the vsyscall page to be
> 'filtered' to the 3 allowed system calls rather efficiently, via a
> second level check.
>
> This second check does not affect the fastpath, and it could be put
> behind a CONFIG_COMPAT_VSYSCALL deprecation define once glibc does
> not put vsyscall references anywhere - but we could even keep it
> around forever, as this way it's defanged permanently.

I'm confused.  Are you thinking about the 32-bit vDSO?  I think that
64-bit code puts syscall instructions all over the place.

--Andy

>
> Thanks,
>
>         Ingo
>
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