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

Jamie Lokier
2004-02-03T08:52:33Z

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