diff options
authorAndy Lutomirski <luto@kernel.org>2015-09-20 16:32:05 -0700
committerSasha Levin <sasha.levin@oracle.com>2015-10-27 22:14:57 -0400
commita70046a8f849fb1a98c5aee0c3504ddf61461eab (patch)
parentc735802ffff335a033b1fba5efd26d778d7b43d6 (diff)
x86/nmi/64: Fix a paravirt stack-clobbering bug in the NMI code
[ Upstream commit 83c133cf11fb0e68a51681447e372489f052d40e ] 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> Cc: stable@vger.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: Sasha Levin <sasha.levin@oracle.com>
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 90b24fecaf43..a3255ca219ea 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1491,9 +1491,11 @@ 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.
movq %rsp, %rdx
movq PER_CPU_VAR(kernel_stack), %rsp