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authorAndy Lutomirski <luto@kernel.org>2015-09-20 16:32:05 -0700
committerJiri Slaby <jslaby@suse.cz>2015-10-07 09:24:43 +0200
commita6f39d84d08b0e9d7f7e8bcb3d845ed676dd4e52 (patch)
tree1ae3be0e7ded351c3b7e1204ca0d6d1a87d67db7 /arch
parentc0007620430f97d3b92bb00df807021721790425 (diff)
downloadlwn-a6f39d84d08b0e9d7f7e8bcb3d845ed676dd4e52.tar.gz
lwn-a6f39d84d08b0e9d7f7e8bcb3d845ed676dd4e52.zip
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: Jiri Slaby <jslaby@suse.cz>
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 7ed99df028ca..2bafcb32941e 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1727,9 +1727,12 @@ 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