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

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Message-ID: <lsq.1589984009.631316172@decadent.org.uk>
Date:   Wed, 20 May 2020 15:14:45 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Andrew Honig" <ahonig@...gle.com>, "Nick Finco" <nifi@...gle.com>,
        "Marios Pomonis" <pomonis@...gle.com>,
        "Jim Mattson" <jmattson@...gle.com>
Subject: [PATCH 3.16 77/99] KVM: x86: Refactor picdev_write() to prevent
 Spectre-v1/L1TF attacks

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

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

From: Marios Pomonis <pomonis@...gle.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 <nifi@...gle.com>
Signed-off-by: Marios Pomonis <pomonis@...gle.com>
Reviewed-by: Andrew Honig <ahonig@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
[bwh: Backported to 3.16: pic_{,un}lock() are called outside the switch]
Signed-off-by: Ben Hutchings <ben@...adent.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: