Messages in this thread | | | Date | Mon, 27 Feb 2012 13:29:47 -0800 | From | Greg KH <> | Subject | Re: [tip:x86/urgent] x86/nmi: Test saved %cs in NMI to determine nested NMI case |
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On Mon, Feb 20, 2012 at 11:51:41AM -0500, Steven Rostedt wrote: > On Mon, 2012-02-20 at 03:47 -0800, tip-bot for Steven Rostedt wrote: > > Commit-ID: 45d5a1683c04be28abdf5c04c27b1417e0374486 > > Gitweb: http://git.kernel.org/tip/45d5a1683c04be28abdf5c04c27b1417e0374486 > > Author: Steven Rostedt <rostedt@goodmis.org> > > AuthorDate: Sun, 19 Feb 2012 16:43:37 -0500 > > Committer: Ingo Molnar <mingo@elte.hu> > > CommitDate: Mon, 20 Feb 2012 09:09:57 +0100 > > > > x86/nmi: Test saved %cs in NMI to determine nested NMI case > > > > Currently, the NMI handler tests if it is nested by checking the > > special variable saved on the stack (set during NMI handling) > > and whether the saved stack is the NMI stack as well (to prevent > > the race when the variable is set to zero). > > > > But userspace may set their %rsp to any value as long as they do > > not derefence it, and it may make it point to the NMI stack, > > which will prevent NMIs from triggering while the userspace app > > is running. (I tested this, and it is indeed the case) > > > > Add another check to determine nested NMIs by looking at the > > saved %cs (code segment register) and making sure that it is the > > kernel code segment. > > > > Signed-off-by: Steven Rostedt <rostedt@goodmis.org> > > Cc: H. Peter Anvin <hpa@zytor.com> > > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> > > Cc: Linus Torvalds <torvalds@linux-foundation.org> > > Cc: <stable@kernel.org> > > Just so that we do not confuse Greg, the bug was introduced in the 3.3 > merge window. It does not exist in 3.2 or earlier.
Thanks for letting me know, I would have been confused :)
greg k-h
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