Messages in this thread | | | Date | Mon, 16 May 2011 23:53:04 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v4 0/6] Micro-optimize vclock_gettime |
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On Mon, 16 May 2011, Andi Kleen wrote: > Andrew Lutomirski <luto@mit.edu> writes: > > Longer term, it would be nice to mark the vsyscall page NX. That > > involves a few things: > > Why NX? What would make sense is to call the VDSO from it. > The problem is that the vDSO is randomized and there's no good memory > location to store the pointer to it. > > The real reason for all this dance is to have some less non randomized > code around. What I implemented back then was instead code to patch out > the SYSCALL in there if not needed to lower the attack surface (not sure > if that still works though, but that was the idea). For most cases > (TSC/HPET read) it's not needed. > > Checking: someone removed the code meanwhile.
For a damned good reason.
> > And we won't have a > > syscall instruction sitting at a predictable address. > > The easy way to fix this is to just re-add the patching.
If you can address _all_ reasons why it was removed then we might revisit that issue, but that's going to be an interesting patch.
Thanks,
tglx
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