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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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