linux-kernel - [PATCH 3.16 78/99] KVM: x86: Protect ioapic_read

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Message-ID: <lsq.1589984009.341862027@decadent.org.uk>
Date:   Wed, 20 May 2020 15:14:46 +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>,
        "Jim Mattson" <jmattson@...gle.com>,
        "Marios Pomonis" <pomonis@...gle.com>,
        "Nick Finco" <nifi@...gle.com>, "Andrew Honig" <ahonig@...gle.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>
Subject: [PATCH 3.16 78/99] KVM: x86: Protect ioapic_read_indirect() from
 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 8c86405f606ca8508b8d9280680166ca26723695 upstream.

This fixes a Spectre-v1/L1TF vulnerability in ioapic_read_indirect().
This function contains index computations based on the
(attacker-controlled) IOREGSEL register.

Fixes: a2c118bfab8b ("KVM: Fix bounds checking in ioapic indirect register reads (CVE-2013-1798)")

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: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 virt/kvm/ioapic.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -36,6 +36,7 @@
 #include <linux/io.h>
 #include <linux/slab.h>
 #include <linux/export.h>
+#include <linux/nospec.h>
 #include <asm/processor.h>
 #include <asm/page.h>
 #include <asm/current.h>
@@ -73,13 +74,14 @@ static unsigned long ioapic_read_indirec
 	default:
 		{
 			u32 redir_index = (ioapic->ioregsel - 0x10) >> 1;
-			u64 redir_content;
+			u64 redir_content = ~0ULL;
 
-			if (redir_index < IOAPIC_NUM_PINS)
-				redir_content =
-					ioapic->redirtbl[redir_index].bits;
-			else
-				redir_content = ~0ULL;
+			if (redir_index < IOAPIC_NUM_PINS) {
+				u32 index = array_index_nospec(
+					redir_index, IOAPIC_NUM_PINS);
+
+				redir_content = ioapic->redirtbl[index].bits;
+			}
 
 			result = (ioapic->ioregsel & 0x1) ?
 			    (redir_content >> 32) & 0xffffffff :