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    Subject[PATCH 3.13 106/162] KVM: x86: Fix far-jump to non-canonical check
    Date
    3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Nadav Amit <namit@cs.technion.ac.il>

    commit 7e46dddd6f6cd5dbf3c7bd04a7e75d19475ac9f2 upstream.

    Commit d1442d85cc30 ("KVM: x86: Handle errors when RIP is set during far
    jumps") introduced a bug that caused the fix to be incomplete. Due to
    incorrect evaluation, far jump to segment with L bit cleared (i.e., 32-bit
    segment) and RIP with any of the high bits set (i.e, RIP[63:32] != 0) set may
    not trigger #GP. As we know, this imposes a security problem.

    In addition, the condition for two warnings was incorrect.

    Fixes: d1442d85cc30ea75f7d399474ca738e0bc96f715
    Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
    Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
    [Add #ifdef CONFIG_X86_64 to avoid complaints of undefined behavior. - Paolo]
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    [ kamal: backport to 3.13-stable: omitted WARN_ON fixes (not in 3.13) ]
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    arch/x86/kvm/emulate.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
    index a440bea..4ae37e7 100644
    --- a/arch/x86/kvm/emulate.c
    +++ b/arch/x86/kvm/emulate.c
    @@ -581,12 +581,14 @@ static inline int assign_eip_far(struct x86_emulate_ctxt *ctxt, ulong dst,
    case 4:
    ctxt->_eip = (u32)dst;
    break;
    +#ifdef CONFIG_X86_64
    case 8:
    if ((cs_l && is_noncanonical_address(dst)) ||
    - (!cs_l && (dst & ~(u32)-1)))
    + (!cs_l && (dst >> 32) != 0))
    return emulate_gp(ctxt, 0);
    ctxt->_eip = dst;
    break;
    +#endif
    default:
    WARN(1, "unsupported eip assignment size\n");
    }
    --
    1.9.1


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