commit: 45d5a1683c04be28abdf5c04c27b1417e0374486 From: Steven Rostedt <[email protected]> Date: Sun, 19 Feb 2012 16:43:37 -0500 Subject: 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 <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/kernel/entry_64.S | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 3fe8239..debd851 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -1532,6 +1532,13 @@ ENTRY(nmi) pushq_cfi %rdx /* + * If %cs was not the kernel segment, then the NMI triggered in user + * space, which means it is definitely not nested. + */ + cmp $__KERNEL_CS, 16(%rsp) + jne first_nmi + + /* * Check the special variable on the stack to see if NMIs are * executing. */ -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
