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Mathieu Desnoyers pointed out a case that can cause issues with NMIs running on the debug stack: int3 -> interrupt -> NMI -> int3 Because the interrupt changes the stack, the NMI will not see that it preempted the debug stack. Looking deeper at this case, interrupts only happen when the int3 is from userspace or in an a location in the exception table (fixup). userspace -> int3 -> interurpt -> NMI -> int3 All other int3s that happen in the kernel should be processed without ever enabling interrupts, as the do_trap() call will panic the kernel if it is called to process any other location within the kernel. Adding a counter around the sections that enable interrupts while using the debug stack allows the NMI to also check that case. If the NMI sees that it either interrupted a task using the debug stack or the debug counter is non-zero, then it will have to change the IDT table to make the int3 not change stacks (which will corrupt the stack if it does). Note, I had to move the debug_usage functions out of processor.h and into debugreg.h because of the static inlined functions to inc and dec the debug_usage counter. __get_cpu_var() requires smp.h which includes processor.h, and would fail to build. Link: http://lkml.kernel.org/r/1323976535.23971.112.camel@gandalf.stny.rr.com Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: H. Peter Anvin <hpa@linux.intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Paul Turner <pjt@google.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> |
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