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