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

[Andi Kleen]

> +What:	CONFIG_UNSAFE_VSYSCALLS (x86_64)
> +When:	When glibc 2.14 or newer is ubitquitous.  Perhaps mid-2012.
> +Why:	Having user-executable code at a fixed address is a security problem.
> +	Turning off CONFIG_UNSAFE_VSYSCALLS mostly removes the risk but will
> +	make the time() function slower on glibc versions 2.13 and below.

I disagree with this description (and the whole idea really)

First it's time+gettimeofday+vgetcu, not just time.

A more accurate description is 

"will make all x86-64 Linux programs written to the original pre
vDSO syscall ABI significantly slower"

And the assumption that all world is using glibc is still as bad
as it was on the first po.st

And it's still a bad idea. Especially since there's a much better
alternative anyways for the "security problem" which has none of 
these drawbacks.

-Andi
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