Re: [PATCH 2/3] x86/altp2m: Add a hvmop for setting the suppress #VE bit

[Tamas K Lengyel <tamas@tklengyel.com>]

On Thu, May 18, 2017 at 9:07 AM, Adrian Pop <apop@bitdefender.com> wrote:
> Introduce a new hvmop, HVMOP_altp2m_set_suppress_ve, which allows a
> domain to change the value of the #VE suppress bit for a page.
>
> Signed-off-by: Adrian Pop <apop@bitdefender.com>
> ---
>  xen/arch/x86/hvm/hvm.c          | 14 ++++++++++++
>  xen/arch/x86/mm/mem_access.c    | 48 +++++++++++++++++++++++++++++++++++++++++
>  xen/include/public/hvm/hvm_op.h | 15 +++++++++++++
>  xen/include/xen/mem_access.h    |  3 +++
>  4 files changed, 80 insertions(+)
>
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 2e76c2345b..eb01527c5b 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -4356,6 +4356,7 @@ static int do_altp2m_op(
>      case HVMOP_altp2m_destroy_p2m:
>      case HVMOP_altp2m_switch_p2m:
>      case HVMOP_altp2m_set_mem_access:
> +    case HVMOP_altp2m_set_suppress_ve:
>      case HVMOP_altp2m_change_gfn:
>          break;
>      default:
> @@ -4472,6 +4473,19 @@ static int do_altp2m_op(
>                                      a.u.set_mem_access.view);
>          break;
>
> +    case HVMOP_altp2m_set_suppress_ve:
> +        if ( a.u.set_suppress_ve.pad1 || a.u.set_suppress_ve.pad2 )
> +            rc = -EINVAL;
> +        else
> +        {
> +            gfn_t gfn = _gfn(a.u.set_mem_access.gfn);
> +            unsigned int altp2m_idx = a.u.set_mem_access.view;
> +            uint8_t suppress_ve = a.u.set_suppress_ve.suppress_ve;
> +
> +            rc = p2m_set_suppress_ve(d, gfn, suppress_ve, altp2m_idx);
> +        }
> +        break;
> +
>      case HVMOP_altp2m_change_gfn:
>          if ( a.u.change_gfn.pad1 || a.u.change_gfn.pad2 )
>              rc = -EINVAL;
> diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
> index d0b0767855..b9e611d3db 100644
> --- a/xen/arch/x86/mm/mem_access.c
> +++ b/xen/arch/x86/mm/mem_access.c
> @@ -466,6 +466,54 @@ int p2m_get_mem_access(struct domain *d, gfn_t gfn, xenmem_access_t *access)
>  }
>
>  /*
> + * Set/clear the #VE suppress bit for a page.  Only available on VMX.
> + */
> +int p2m_set_suppress_ve(struct domain *d, gfn_t gfn, uint8_t suppress_ve,
> +                        unsigned int altp2m_idx)
> +{
> +    struct p2m_domain *host_p2m = p2m_get_hostp2m(d);
> +    struct p2m_domain *ap2m = NULL;
> +    struct p2m_domain *p2m = NULL;
> +    mfn_t mfn;
> +    p2m_access_t a;
> +    p2m_type_t t;
> +    unsigned long gfn_l;
> +    int rc = 0;
> +
> +    if ( !cpu_has_vmx )
> +        return -EOPNOTSUPP;
> +
> +    if ( altp2m_idx > 0 )
> +    {
> +        if ( altp2m_idx >= MAX_ALTP2M ||
> +                d->arch.altp2m_eptp[altp2m_idx] == mfn_x(INVALID_MFN) )
> +            return -EINVAL;
> +
> +        p2m = ap2m = d->arch.altp2m_p2m[altp2m_idx];
> +    }
> +    else
> +    {
> +        p2m = host_p2m;
> +    }


IMHO there should be some further checks here to verify that the
domain has issued HVMOP_altp2m_vcpu_enable_notify before and that it
was allowed (ie. this hypercall should not be able to enable the
suppress_bit if there is no veinfo_gfn). That said, is there anything
that would prevent a malicious application issuing rouge altp2m HVMOPs
from messing with this if it is activated (which I guess stands for
the rest of the altp2m ops too)?

> +
> +    p2m_lock(host_p2m);
> +    if ( ap2m )
> +        p2m_lock(ap2m);
> +
> +    gfn_l = gfn_x(gfn);
> +    mfn = p2m->get_entry(p2m, gfn_l, &t, &a, 0, NULL, NULL);
> +    if ( !mfn_valid(mfn) )
> +        return -ESRCH;
> +    rc = p2m->set_entry(p2m, gfn_l, mfn, PAGE_ORDER_4K, t, a,
> +                        suppress_ve);
> +    if ( ap2m )
> +        p2m_unlock(ap2m);
> +    p2m_unlock(host_p2m);
> +
> +    return rc;
> +}
> +
> +/*
>   * Local variables:
>   * mode: C
>   * c-file-style: "BSD"
> diff --git a/xen/include/public/hvm/hvm_op.h b/xen/include/public/hvm/hvm_op.h
> index bc00ef0e65..9736092f58 100644
> --- a/xen/include/public/hvm/hvm_op.h
> +++ b/xen/include/public/hvm/hvm_op.h
> @@ -231,6 +231,18 @@ struct xen_hvm_altp2m_set_mem_access {
>  typedef struct xen_hvm_altp2m_set_mem_access xen_hvm_altp2m_set_mem_access_t;
>  DEFINE_XEN_GUEST_HANDLE(xen_hvm_altp2m_set_mem_access_t);
>
> +struct xen_hvm_altp2m_set_suppress_ve {
> +    /* view */
> +    uint16_t view;
> +    uint8_t suppress_ve;
> +    uint8_t pad1;
> +    uint32_t pad2;
> +    /* gfn */
> +    uint64_t gfn;
> +};
> +typedef struct xen_hvm_altp2m_set_suppress_ve xen_hvm_altp2m_set_suppress_ve_t;
> +DEFINE_XEN_GUEST_HANDLE(xen_hvm_altp2m_set_suppress_ve_t);
> +
>  struct xen_hvm_altp2m_change_gfn {
>      /* view */
>      uint16_t view;
> @@ -262,6 +274,8 @@ struct xen_hvm_altp2m_op {
>  #define HVMOP_altp2m_set_mem_access       7
>  /* Change a p2m entry to have a different gfn->mfn mapping */
>  #define HVMOP_altp2m_change_gfn           8
> +/* Set the "Suppress #VE" bit on a page */
> +#define HVMOP_altp2m_set_suppress_ve      9
>      domid_t domain;
>      uint16_t pad1;
>      uint32_t pad2;
> @@ -270,6 +284,7 @@ struct xen_hvm_altp2m_op {
>          struct xen_hvm_altp2m_vcpu_enable_notify enable_notify;
>          struct xen_hvm_altp2m_view               view;
>          struct xen_hvm_altp2m_set_mem_access     set_mem_access;
> +        struct xen_hvm_altp2m_set_suppress_ve    set_suppress_ve;
>          struct xen_hvm_altp2m_change_gfn         change_gfn;
>          uint8_t pad[64];
>      } u;
> diff --git a/xen/include/xen/mem_access.h b/xen/include/xen/mem_access.h
> index 5ab34c1553..b6e6a7650a 100644
> --- a/xen/include/xen/mem_access.h
> +++ b/xen/include/xen/mem_access.h
> @@ -78,6 +78,9 @@ long p2m_set_mem_access_multi(struct domain *d,
>   */
>  int p2m_get_mem_access(struct domain *d, gfn_t gfn, xenmem_access_t *access);
>
> +int p2m_set_suppress_ve(struct domain *d, gfn_t gfn, uint8_t suppress_ve,
> +                        unsigned int altp2m_idx);
> +
>  #ifdef CONFIG_HAS_MEM_ACCESS
>  int mem_access_memop(unsigned long cmd,
>                       XEN_GUEST_HANDLE_PARAM(xen_mem_access_op_t) arg);
> --
> 2.12.1
>
>
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