4.9-stable patches

[thirdparty/kernel/stable-queue.git] / releases / 2.6.27.46 / kvm-x86-emulator-limit-insns-to-15-bytes.patch

From: Avi Kivity <avi@redhat.com>
Date: Tue, 24 Nov 2009 13:20:15 +0000 (+0200)
Subject: KVM: x86 emulator: limit instructions to 15 bytes

commit eb3c79e64a70fb8f7473e30fa07e89c1ecc2c9bb upstream

[ <cebbert@redhat.com>: backport to 2.6.27 ]

While we are never normally passed an instruction that exceeds 15 bytes,
smp games can cause us to attempt to interpret one, which will cause
large latencies in non-preempt hosts.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 arch/x86/kvm/x86_emulate.c        |    5 ++++-
 include/asm-x86/kvm_x86_emulate.h |    2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -581,6 +581,9 @@ static int do_insn_fetch(struct x86_emul
 {
 	int rc = 0;
 
+	/* x86 instructions are limited to 15 bytes. */
+	if (eip + size - ctxt->decode.eip_orig > 15)
+		return X86EMUL_UNHANDLEABLE;
 	eip += ctxt->cs_base;
 	while (size--) {
 		rc = do_fetch_insn_byte(ctxt, ops, eip++, dest++);
@@ -839,7 +842,7 @@ x86_decode_insn(struct x86_emulate_ctxt
 	/* Shadow copy of register state. Committed on successful emulation. */
 
 	memset(c, 0, sizeof(struct decode_cache));
-	c->eip = ctxt->vcpu->arch.rip;
+	c->eip = c->eip_orig = ctxt->vcpu->arch.rip;
 	ctxt->cs_base = seg_base(ctxt, VCPU_SREG_CS);
 	memcpy(c->regs, ctxt->vcpu->arch.regs, sizeof c->regs);
 
--- a/include/asm-x86/kvm_x86_emulate.h
+++ b/include/asm-x86/kvm_x86_emulate.h
@@ -128,7 +128,7 @@ struct decode_cache {
 	u8 seg_override;
 	unsigned int d;
 	unsigned long regs[NR_VCPU_REGS];
-	unsigned long eip;
+	unsigned long eip, eip_orig;
 	/* modrm */
 	u8 modrm;
 	u8 modrm_mod;