[PATCH 3.19.y-ckt 006/107] x86/nmi/64: Remove asm code that saves cr2

From: Kamal Mostafa
Date: Wed Aug 05 2015 - 18:26:15 EST


3.19.8-ckt5 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@xxxxxxxxxx>

commit 0e181bb58143cb4a2e8f01c281b0816cd0e4798e upstream.

Now that do_nmi saves cr2, we don't need to save it in asm.

This is a prerequisity for the fix for CVE-2015-3290.

Reviewed-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Acked-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
[bwh: Backported to 4.0: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Acked-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
Acked-by: Andy Whitcroft <apw@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
---
arch/x86/kernel/entry_64.S | 18 ------------------
1 file changed, 18 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 315f8e9..edffe680 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1651,29 +1651,11 @@ end_repeat_nmi:
call save_paranoid
DEFAULT_FRAME 0

- /*
- * Save off the CR2 register. If we take a page fault in the NMI then
- * it could corrupt the CR2 value. If the NMI preempts a page fault
- * handler before it was able to read the CR2 register, and then the
- * NMI itself takes a page fault, the page fault that was preempted
- * will read the information from the NMI page fault and not the
- * origin fault. Save it off and restore it if it changes.
- * Use the r12 callee-saved register.
- */
- movq %cr2, %r12
-
/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
movq %rsp,%rdi
movq $-1,%rsi
call do_nmi

- /* Did the NMI take a page fault? Restore cr2 if it did */
- movq %cr2, %rcx
- cmpq %rcx, %r12
- je 1f
- movq %r12, %cr2
-1:
-
testl %ebx,%ebx /* swapgs needed? */
jnz nmi_restore
nmi_swapgs:
--
1.9.1

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