[PATCH 3.16 77/99] KVM: x86: Refactor picdev_write() to prevent Spectre-v1/L1TF attacks

[Ben Hutchings]

3.16.84-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Marios Pomonis <pomonis@xxxxxxxxxx>

commit 14e32321f3606e4b0970200b6e5e47ee6f1e6410 upstream.

This fixes a Spectre-v1/L1TF vulnerability in picdev_write().
It replaces index computations based on the (attacked-controlled) port
number with constants through a minor refactoring.

Fixes: 85f455f7ddbe ("KVM: Add support for in-kernel PIC emulation")

Signed-off-by: Nick Finco <nifi@xxxxxxxxxx>
Signed-off-by: Marios Pomonis <pomonis@xxxxxxxxxx>
Reviewed-by: Andrew Honig <ahonig@xxxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
[bwh: Backported to 3.16: pic_{,un}lock() are called outside the switch]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/arch/x86/kvm/i8259.c
+++ b/arch/x86/kvm/i8259.c
@@ -486,9 +486,11 @@ static int picdev_write(struct kvm_pic *
 	switch (addr) {
 	case 0x20:
 	case 0x21:
+		pic_ioport_write(&s->pics[0], addr, data);
+		break;
 	case 0xa0:
 	case 0xa1:
-		pic_ioport_write(&s->pics[addr >> 7], addr, data);
+		pic_ioport_write(&s->pics[1], addr, data);
 		break;
 	case 0x4d0:
 	case 0x4d1: