Re: [PATCH v16 01/10] x86: add generic resource (e.g. MSR) access hypercall

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 25/09/14 11:19, Chao Peng wrote:
> Add a generic resource access hypercall for tool stack or other
> components, e.g., accessing MSR, port I/O, etc.
>
> Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  xen/arch/x86/platform_hypercall.c        |   90 ++++++++++++++++++++++++++++++
>  xen/arch/x86/x86_64/platform_hypercall.c |    4 ++
>  xen/include/public/platform.h            |   23 ++++++++
>  xen/include/xlat.lst                     |    2 +
>  4 files changed, 119 insertions(+)
>
> diff --git a/xen/arch/x86/platform_hypercall.c b/xen/arch/x86/platform_hypercall.c
> index 2162811..081d9f5 100644
> --- a/xen/arch/x86/platform_hypercall.c
> +++ b/xen/arch/x86/platform_hypercall.c
> @@ -61,6 +61,68 @@ long cpu_down_helper(void *data);
>  long core_parking_helper(void *data);
>  uint32_t get_cur_idle_nums(void);
>  
> +struct xen_resource_access {
> +    int32_t ret;
> +    uint32_t nr;
> +    XEN_GUEST_HANDLE(xenpf_resource_data_t) data;
> +};
> +
> +static bool_t allow_access_msr(unsigned int msr)
> +{
> +    return 0;
> +}
> +
> +static void resource_access(void *info)
> +{
> +    struct xen_resource_access *ra = info;
> +    xenpf_resource_data_t data;
> +    int ret = 0;
> +    unsigned int i;
> +
> +    for ( i = 0; i < ra->nr; i++ )
> +    {
> +        if ( copy_from_guest_offset(&data, ra->data, i, 1) )

You cannot use copy_{to,from}_guest() here.  You are almost certainly on
the wrong cpu, and running on the wrong set of pagetables.

At best, you will copy bogus data from the wrong process/domain, and
likely corrupt it when copying back.

> +        {
> +            ret = -EFAULT;
> +            break;
> +        }
> +
> +        if ( data.rsvd ) {
> +            ret = -EINVAL;
> +            break;
> +        }
> +
> +        switch ( data.cmd )
> +        {
> +        case XEN_RESOURCE_OP_MSR_READ:
> +        case XEN_RESOURCE_OP_MSR_WRITE:
> +            if ( data.idx >> 32 )
> +                ret = -EINVAL;
> +            else if ( !allow_access_msr(data.idx) )
> +                ret = -EACCES;
> +            else if ( data.cmd == XEN_RESOURCE_OP_MSR_READ )
> +                ret = rdmsr_safe(data.idx, data.val);
> +            else
> +                ret = wrmsr_safe(data.idx, data.val);
> +            break;
> +        default:
> +            ret = -EINVAL;
> +            break;
> +        }
> +
> +        if ( ret )
> +            break;
> +
> +        if ( copy_to_guest_offset(ra->data, i, &data, 1) )
> +        {
> +            ret = -EFAULT;
> +            break;
> +        }
> +    }
> +
> +    ra->ret = ret;
> +}
> +
>  ret_t do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
>  {
>      ret_t ret = 0;
> @@ -601,6 +663,34 @@ ret_t do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
>      }
>      break;
>  
> +    case XENPF_resource_op:
> +    {
> +        struct xen_resource_access ra;
> +        struct xenpf_resource_op *rsc_op = &op->u.resource_op;
> +        unsigned int cpu = smp_processor_id();
> +
> +        ra.nr = rsc_op->nr;
> +        ra.data = rsc_op->data;

You must do all copy_{from,to}_user() here, and strictly only pass Xen
pointers to resource_access().

This means you will need to xmalloc() yourself some space for the
xenpf_resource_data_t array.


On a different note, you need to enforce a maximum resource_op.nr of
something rather low to (16/32 perhaps?) to prevent a toolstack asking
for 0xffffffff non-preemptible operations.

~Andrew

> +
> +        if ( rsc_op->cpu == cpu )
> +            resource_access(&ra);
> +        else if ( cpu_online(rsc_op->cpu) )
> +            on_selected_cpus(cpumask_of(rsc_op->cpu),
> +                         resource_access, &ra, 1);
> +        else
> +        {
> +            ret = -ENODEV;
> +            break;
> +        }
> +
> +        if ( ra.ret )
> +        {
> +            ret = ra.ret;
> +            break;
> +        }
> +    }
> +    break;
> +
>      default:
>          ret = -ENOSYS;
>          break;
> diff --git a/xen/arch/x86/x86_64/platform_hypercall.c b/xen/arch/x86/x86_64/platform_hypercall.c
> index b6f380e..4db6622 100644
> --- a/xen/arch/x86/x86_64/platform_hypercall.c
> +++ b/xen/arch/x86/x86_64/platform_hypercall.c
> @@ -32,6 +32,10 @@ CHECK_pf_pcpu_version;
>  CHECK_pf_enter_acpi_sleep;
>  #undef xen_pf_enter_acpi_sleep
>  
> +#define xen_pf_resource_data xenpf_resource_data
> +CHECK_pf_resource_data;
> +#undef xen_pf_resource_data
> +
>  #define COMPAT
>  #define _XEN_GUEST_HANDLE(t) XEN_GUEST_HANDLE(t)
>  #define _XEN_GUEST_HANDLE_PARAM(t) XEN_GUEST_HANDLE_PARAM(t)
> diff --git a/xen/include/public/platform.h b/xen/include/public/platform.h
> index 053b9fa..e4d9091 100644
> --- a/xen/include/public/platform.h
> +++ b/xen/include/public/platform.h
> @@ -527,6 +527,28 @@ struct xenpf_core_parking {
>  typedef struct xenpf_core_parking xenpf_core_parking_t;
>  DEFINE_XEN_GUEST_HANDLE(xenpf_core_parking_t);
>  
> +#define XENPF_resource_op   61
> +
> +#define XEN_RESOURCE_OP_MSR_READ  0
> +#define XEN_RESOURCE_OP_MSR_WRITE 1
> +
> +struct xenpf_resource_data {
> +    uint32_t cmd;       /* XEN_RESOURCE_OP_* */
> +    uint32_t rsvd;
> +    uint64_t idx;
> +    uint64_t val;
> +};
> +typedef struct xenpf_resource_data xenpf_resource_data_t;
> +DEFINE_XEN_GUEST_HANDLE(xenpf_resource_data_t);
> +
> +struct xenpf_resource_op {
> +    uint32_t nr;    /* number of data entry */
> +    uint32_t cpu;   /* which cpu to run */
> +    XEN_GUEST_HANDLE(xenpf_resource_data_t) data;
> +};
> +typedef struct xenpf_resource_op xenpf_resource_op_t;
> +DEFINE_XEN_GUEST_HANDLE(xenpf_resource_op_t);
> +
>  /*
>   * ` enum neg_errnoval
>   * ` HYPERVISOR_platform_op(const struct xen_platform_op*);
> @@ -553,6 +575,7 @@ struct xen_platform_op {
>          struct xenpf_cpu_hotadd        cpu_add;
>          struct xenpf_mem_hotadd        mem_add;
>          struct xenpf_core_parking      core_parking;
> +        struct xenpf_resource_op       resource_op;
>          uint8_t                        pad[128];
>      } u;
>  };
> diff --git a/xen/include/xlat.lst b/xen/include/xlat.lst
> index 9a35dd7..100fcf5 100644
> --- a/xen/include/xlat.lst
> +++ b/xen/include/xlat.lst
> @@ -88,6 +88,8 @@
>  ?	xenpf_enter_acpi_sleep		platform.h
>  ?	xenpf_pcpuinfo			platform.h
>  ?	xenpf_pcpu_version		platform.h
> +?	xenpf_resource_op		platform.h
> +?	xenpf_resource_data		platform.h
>  !	sched_poll			sched.h
>  ?	sched_remote_shutdown		sched.h
>  ?	sched_shutdown			sched.h