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KVM: x86 emulator: limit instructions to 15 bytes

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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>
This commit is contained in:
Avi Kivity 2009-11-24 15:20:15 +02:00
parent d7b0b5eb30
commit eb3c79e64a
2 changed files with 5 additions and 2 deletions
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2
arch/x86/include/asm/kvm_emulate.h
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@ -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;

5
arch/x86/kvm/emulate.c
View File

@ -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);