Re: [PATCH v4 10/10] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to feature-removal-schedule

[Andrew Lutomirski]

[Sorry, possible resend.]

On 5/31/11, 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.
>

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

How is this better than v2 of my series, stopping after the int cc fallback?

--Andy

> Thanks,
>
> 	Ingo
>
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