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authorSteven Rostedt <rostedt@goodmis.org>2012-02-19 16:43:37 -0500
committerIngo Molnar <mingo@elte.hu>2012-02-20 09:09:57 +0100
commit45d5a1683c04be28abdf5c04c27b1417e0374486 (patch)
treec8ed3fc0a9ba31df6cf7ac92f39f935c55b55f18 /arch
parent32c3233885eb10ac9cb9410f2f8cd64b8df2b2a1 (diff)
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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> Link: http://lkml.kernel.org/r/1329687817.1561.27.camel@acer.local.home Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/entry_64.S7
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 3fe8239fd8fb..debd851de6ff 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.
*/