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Subject[26/45] KVM: x86 emulator: limit instructions to 15 bytes
2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
commit eb3c79e64a70fb8f7473e30fa07e89c1ecc2c9bb upstream

[ <cebbert@redhat.com>: backport to 2.6.27 ]

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>

---
arch/x86/kvm/x86_emulate.c | 5 ++++-
include/asm-x86/kvm_x86_emulate.h | 2 +-
2 files changed, 5 insertions(+), 2 deletions(-)
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -581,6 +581,9 @@ static int do_insn_fetch(struct x86_emul
{
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++);
@@ -839,7 +842,7 @@ x86_decode_insn(struct x86_emulate_ctxt
/* Shadow copy of register state. Committed on successful emulation. */

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

--- a/include/asm-x86/kvm_x86_emulate.h
+++ b/include/asm-x86/kvm_x86_emulate.h
@@ -128,7 +128,7 @@ 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;



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