From eb3c79e64a70fb8f7473e30fa07e89c1ecc2c9bb Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Tue, 24 Nov 2009 15:20:15 +0200 Subject: [PATCH] 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: Avi Kivity --- arch/x86/include/asm/kvm_emulate.h | 2 +- arch/x86/kvm/emulate.c | 5 ++++- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h index b7ed2c423116..7c18e1230f54 100644 --- a/arch/x86/include/asm/kvm_emulate.h +++ b/arch/x86/include/asm/kvm_emulate.h @@ -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; diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index d226dff47d77..7e8faea4651e 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -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); -- 2.39.5