Commit 83c133cf authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Thomas Gleixner

x86/nmi/64: Fix a paravirt stack-clobbering bug in the NMI code

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: 9b6e6a83 ("x86/nmi/64: Switch stacks on userspace NMI entry")
Reported-and-tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/974bc40edffdb5c2950a5c4977f821a446b76178.1442791737.git.luto@kernel.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent fc57a7c6
...@@ -1190,9 +1190,12 @@ ENTRY(nmi) ...@@ -1190,9 +1190,12 @@ ENTRY(nmi)
* we don't want to enable interrupts, because then we'll end * we don't want to enable interrupts, because then we'll end
* up in an awkward situation in which IRQs are on but NMIs * up in an awkward situation in which IRQs are on but NMIs
* are off. * 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 cld
movq %rsp, %rdx movq %rsp, %rdx
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
......
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