Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 23 Aug 2011 18:07:40 +0100 | From | Al Viro <> | Subject | Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386) |
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On Tue, Aug 23, 2011 at 06:58:18PM +0200, Richard Weinberger wrote:
> What about this hack/solution? > While booting UML can check whether the host's vDSO contains > a SYSCALL instruction. > If so, UML will not make the host's vDSO available to it's > processes...
Note that this is *only* for 32bit side of things. 64bit one works fine...
I wouldn't search for SYSCALL in vdso, BTW - not when we have a good way to trigger that crap and recognize it.
At boot time, fork a child. Have it traced with PTRACE_SYSCALL. Let it put recognizable values in registers and call __kernel_vsyscall(). Then let the parent do one more PTRACE_SYSCALL, then PTRACE_POKEUSER and set ebp to 0x69696969. PTRACE_CONT the sucker and let it report what it sees in ecx. If it's what we'd put there - fine, it looks safe. If it's 0x69696969 - we have a problem, no vdso for us.
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