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

[Andrew Lutomirski]

On Tue, May 31, 2011 at 2:34 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>> +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"

Well, if this series goes in, then gettimeofday and getcpu are already
slower.  It's just time that would get even slower later on.

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

As opposed to?

uclibc and klibc don't appear to use vsyscalls or the vdso.

dietlibc is hardcoded to use the vsyscall.  Are there any
performance-critical programs using dietlibc?

I don't think that Bionic runs on any released x86-64 systems.

>
> 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.

What's the alternative?

--Andy
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