Messages in this thread | ![/](/images/icornerl.gif) | | From | Andrew Lutomirski <> | Date | Thu, 11 Aug 2011 09:27:20 -0400 | Subject | Re: [RFC v2] x86-64: Allow emulated vsyscalls from user addresses |
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On Thu, Aug 11, 2011 at 9:16 AM, Pavel Machek <pavel@ucw.cz> wrote: > Hi! > >> They trace control flow through the vsyscall page and recompile that >> code somewhere else. Then they expect it to work. DynamoRIO >> (http://dynamorio.org/) and Pin (http://www.pintool.org/) are >> affected. They crash when tracing programs that use vsyscalls. >> Valgrind is smart enough not to cause problems. It crashes on the >> getcpu vsyscall, but that has nothing to do with emulation. >> >> This patch makes each of the three vsyscall entries use a different >> vector so that they can work when relocated. It assumes that the >> code that relocates them is okay with the int instruction acting >> like ret. DynamoRIO at least appears to work. > > int acting as ret is seriously weird semantics. And no, invalid > syscall parameters will not cause segfault, just return of -EFAULT. So > ... can this be changed?
Can which be changed? int acting as ret already was (in a different patch, now in tip/x86/vdso), although I still think that user code should do its best to make no assumptions about the vsyscall page.
invalid syscall parameters do indeed return -EFAULT, but invalid *v*syscall parameters will segfault in 3.0 and before, since the vsyscall implementation is just user code and has no exception handling.
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