Messages in this thread | | | Date | Mon, 10 Oct 2011 13:19:12 +0200 | Subject | Re: [3.1 patch] x86: default to vsyscall=native | From | richard -rw- weinberger <> |
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On Fri, Oct 7, 2011 at 2:48 AM, Andrew Lutomirski <luto@mit.edu> wrote: > On Thu, Oct 6, 2011 at 11:34 AM, Linus Torvalds > <torvalds@linux-foundation.org> wrote: >> On Thu, Oct 6, 2011 at 11:16 AM, Andrew Lutomirski <luto@mit.edu> wrote: >>> >>> Fixing it will be annoying because the attached fancier version needs >>> to work, too. I could implement the whole mess in software, but it >>> might be nicer to arrange for uaccess errors to stash some information >>> somewhere (like in the thread_struct cr2 variable). >> >> That should be easy enough to do. Just add it to the >> "fixup_exception()" case in no_context(). > > This code is rather messy. We stash the cr2, err, and trap fields of > sigcontext in thread_struct and we *never* reset them until the next > segfault. So userspace sees stale garbage on every signal that isn't > a (genuine) segfault. I can imagine this breaking UML is remarkably > bizarre ways even without vsyscall emulation because UML actually > seems to rely on that stuff to determine the source of a signal. >
From UML's point of view the current situation is odd. UML will no longer run on top of a default 3.1 kernel.
Why is this odd? One of the major reasons why people are still using UML is because you can run it as non-privileged user on any x86 Linux host. An user which has root privileges can setup and use KVM which is much nicer than UML...
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