Re: [RFC][PATCH] linux-2.6.2-rc2_vsyscall-gtod_B1.patch

[Jamie Lokier]

Ulrich Drepper wrote:
> You got to be kidding.  Some object fixed in the address space which can
> perform system calls.  Nothing is more welcome to somebody trying to
> exploit some bugs.

Two approaches to randomising the vdso address:

  1. Selecting a random address at boot time.  All tasks have the same
     vdso for that run of the kernel.  Advantages: no MSR write at
     each context switch; could patch libsyscall.so at boot time with
     address if we were fanatical about optimisation (i.e. other
     libcs, not Glibc :)  Disadvantages: the attacker may eventually
     learn the address.

  2. Select a random address for every new task.  Advantages: harder
     to guess from studying a machine for a long time.  Disadvantages:
     slower context switches; the gain from randomising each task is
     nothing if all the tasks are very long lived anyway.

-- Jamie
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