KVM: x86 emulator: limit instructions to 15 bytes

commit eb3c79e64a70fb8f7473e30fa07e89c1ecc2c9bb upstream.

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>

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index b7ed2c423116be32942ef23b63e5dc4f09492d9d..7c18e1230f5490f1f7a58bd103302ffcb8bf20b1 100644 (file)
--- 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 1be5cd640e93f2f71b92829fbba082b37bdabe62..e02dbb670d5b56b826cf9394b25300b2dc49c54e 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -613,6 +613,9 @@ 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++);
@@ -871,7 +874,7 @@ 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);