From: Marios Pomonis <pomonis@google.com>
Date: Wed, 11 Dec 2019 20:47:41 +0000 (-0800)
Subject: KVM: x86: Protect x86_decode_insn from Spectre-v1/L1TF attacks
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=113857794697b60391ffc4de71c50ac67233928c;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

KVM: x86: Protect x86_decode_insn from Spectre-v1/L1TF attacks

commit 3c9053a2cae7ba2ba73766a34cea41baa70f57f7 upstream.

This fixes a Spectre-v1/L1TF vulnerability in x86_decode_insn().
kvm_emulate_instruction() (an ancestor of x86_decode_insn()) is an exported
symbol, so KVM should treat it conservatively from a security perspective.

Fixes: 045a282ca415 ("KVM: emulator: implement fninit, fnstsw, fnstcw")

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index ff20ef3fd899..c456a9dbade8 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -21,6 +21,7 @@
  */
 
 #include <linux/kvm_host.h>
+#include <linux/nospec.h>
 #include "kvm_cache_regs.h"
 #include <asm/kvm_emulate.h>
 #include <linux/stringify.h>
@@ -5158,10 +5159,15 @@ done_prefixes:
 			}
 			break;
 		case Escape:
-			if (ctxt->modrm > 0xbf)
-				opcode = opcode.u.esc->high[ctxt->modrm - 0xc0];
-			else
+			if (ctxt->modrm > 0xbf) {
+				size_t size = ARRAY_SIZE(opcode.u.esc->high);
+				u32 index = array_index_nospec(
+					ctxt->modrm - 0xc0, size);
+
+				opcode = opcode.u.esc->high[index];
+			} else {
 				opcode = opcode.u.esc->op[(ctxt->modrm >> 3) & 7];
+			}
 			break;
 		case InstrDual:
 			if ((ctxt->modrm >> 6) == 3)