[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 <pomo...@google.com>

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 <n...@google.com>
Signed-off-by: Marios Pomonis <pomo...@google.com>
Reviewed-by: Andrew Honig <aho...@google.com>
Reviewed-by: Jim Mattson <jmatt...@google.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
[bwh: Backported to 3.16: pic_{,un}lock() are called outside the switch]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- 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: