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authorAndy Lutomirski <luto@kernel.org>2015-09-20 16:32:05 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-10-22 14:39:18 -0700
commit76bdbeab6899465e47817b70b16eae5f5b6d9f19 (patch)
tree27910d493358c614039e2cfcd1059eaa4ed527d3 /arch
parent9b53b9dcfe11b35a27992429fa2e78e8c99769b2 (diff)
x86/nmi/64: Fix a paravirt stack-clobbering bug in the NMI code
commit 83c133cf11fb0e68a51681447e372489f052d40e upstream. The NMI entry code that switches to the normal kernel stack needs to be very careful not to clobber any extra stack slots on the NMI stack. The code is fine under the assumption that SWAPGS is just a normal instruction, but that assumption isn't really true. Use SWAPGS_UNSAFE_STACK instead. This is part of a fix for some random crashes that Sasha saw. Fixes: 9b6e6a8334d5 ("x86/nmi/64: Switch stacks on userspace NMI entry") Reported-and-tested-by: Sasha Levin <sasha.levin@oracle.com> Signed-off-by: Andy Lutomirski <luto@kernel.org> Link: http://lkml.kernel.org/r/974bc40edffdb5c2950a5c4977f821a446b76178.1442791737.git.luto@kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/entry_64.S5
1 files changed, 4 insertions, 1 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e52470a82256..f2f2b97b7cc4 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1747,8 +1747,11 @@ ENTRY(nmi)
* we don't want to enable interrupts, because then we'll end
* up in an awkward situation in which IRQs are on but NMIs
* are off.
+ *
+ * We also must not push anything to the stack before switching
+ * stacks lest we corrupt the "NMI executing" variable.
*/
- SWAPGS
+ SWAPGS_UNSAFE_STACK
cld
movq %rsp, %rdx
movq PER_CPU_VAR(kernel_stack), %rsp