Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit eb3c79e6 authored Nov 24, 2009 by Avi Kivity

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 <avi@redhat.com>

parent d7b0b5eb

arch/x86/include/asm/kvm_emulate.h

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -129,7 +129,7 @@ struct decode_cache {
	u8 seg_override;		u8 seg_override;
	unsigned int d;		unsigned int d;
	unsigned long regs[NR_VCPU_REGS];		unsigned long regs[NR_VCPU_REGS];
	unsigned long eip;		unsigned long eip, eip_orig;
	/* modrm */		/* modrm */
	u8 modrm;		u8 modrm;
	u8 modrm_mod;		u8 modrm_mod;

arch/x86/kvm/emulate.c

+4 −1

Original line number	Original line	Diff line number	Diff line
	@@ -622,6 +622,9 @@ static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,
	{		{
	int rc = 0;		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;		eip += ctxt->cs_base;
	while (size--) {		while (size--) {
	rc = do_fetch_insn_byte(ctxt, ops, eip++, dest++);		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. */		/* Shadow copy of register state. Committed on successful emulation. */

	memset(c, 0, sizeof(struct decode_cache));		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);		ctxt->cs_base = seg_base(ctxt, VCPU_SREG_CS);
	memcpy(c->regs, ctxt->vcpu->arch.regs, sizeof c->regs);		memcpy(c->regs, ctxt->vcpu->arch.regs, sizeof c->regs);