KVM: x86: Refactor picdev_write() to prevent Spectre-v1/L1TF attacks

[ Upstream commit 14e32321f3606e4b0970200b6e5e47ee6f1e6410 ]

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: 85f455f ("KVM: Add support for in-kernel PIC emulation")

Signed-off-by: Nick Finco <nifi@google.com>
Signed-off-by: Marios Pomonis <pomonis@google.com>
Reviewed-by: Andrew Honig <ahonig@google.com>
Cc: stable@vger.kernel.org
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: I48f503d0c0ad3f108d7b23f2edb86664f8b42429

Author: marpom

arch/x86/kvm/i8259.c

@@ -468,10 +468,14 @@ static int picdev_write(struct kvm_pic *s,
 	switch (addr) {
 	case 0x20:
 	case 0x21:
+		pic_lock(s);
+		pic_ioport_write(&s->pics[0], addr, data);
+		pic_unlock(s);
+		break;
 	case 0xa0:
 	case 0xa1:
 		pic_lock(s);
-		pic_ioport_write(&s->pics[addr >> 7], addr, data);
+		pic_ioport_write(&s->pics[1], addr, data);
 		pic_unlock(s);
 		break;
 	case 0x4d0: