Commit eb3c79e6 authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: x86 emulator: limit instructions to 15 bytes 



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.

Cc: stable@kernel.org
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent d7b0b5eb

arch/x86/include/asm/kvm_emulate.h

+1 −1
Original line number Diff line number Diff line
@@ -129,7 +129,7 @@ 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;

arch/x86/kvm/emulate.c

+4 −1
Original line number Diff line number Diff line
@@ -622,6 +622,9 @@ static int do_insn_fetch(struct x86_emulate_ctxt *ctxt, 
{

	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++);
@@ -880,7 +883,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops) 
	/* Shadow copy of register state. Committed on successful emulation. */



	memset(c, 0, sizeof(struct decode_cache));

	c->eip = kvm_rip_read(ctxt->vcpu);

	c->eip = c->eip_orig = kvm_rip_read(ctxt->vcpu);

	ctxt->cs_base = seg_base(ctxt, VCPU_SREG_CS);

	memcpy(c->regs, ctxt->vcpu->arch.regs, sizeof c->regs);