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[Xen-devel] [PATCH] xen/arm: Restrict access to most HVM_PARAM's

Andrew Cooper posted 1 patch 5 years, 11 months ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/xen tags/patchew/20200219193001.28822-1-andrew.cooper3@citrix.com
xen/arch/arm/hvm.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 59 insertions(+), 3 deletions(-)
[Xen-devel] [PATCH] xen/arm: Restrict access to most HVM_PARAM's
Posted by Andrew Cooper 5 years, 11 months ago 
ARM currently has no restrictions on toolstack and guest access to the entire
HVM_PARAM block.  As the monitor feature isn't under security support, this
doesn't need an XSA.

The CALLBACK_IRQ and {STORE,CONSOLE}_{PFN,EVTCHN} details are only exposed
read-only to the guest, while MONITOR_RING_PFN is restricted to only toolstack
access.  No other parameters are used.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien@xen.org>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>

This is only compile tested, and based on my reading of the source.  There
might be other PARAMS needing including.

v2:
 * Drop paging/sharing
 * Clarify comment about {STORE,CONSOLE}_EVTCHN
---
 xen/arch/arm/hvm.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 59 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/hvm.c b/xen/arch/arm/hvm.c
index 76b27c9168..8951b34086 100644
--- a/xen/arch/arm/hvm.c
+++ b/xen/arch/arm/hvm.c
@@ -31,6 +31,57 @@
 
 #include <asm/hypercall.h>
 
+static int hvm_allow_set_param(const struct domain *d, unsigned int param)
+{
+    switch ( param )
+    {
+        /*
+         * The following parameters are intended for toolstack usage only.
+         * They may not be set by the domain.
+         *
+         * The {STORE,CONSOLE}_EVTCHN values will need to become read/write to
+         * the guest (not just the toolstack) if a new ABI hasn't appeared by
+         * the time migration support is added.
+         */
+    case HVM_PARAM_CALLBACK_IRQ:
+    case HVM_PARAM_STORE_PFN:
+    case HVM_PARAM_STORE_EVTCHN:
+    case HVM_PARAM_CONSOLE_PFN:
+    case HVM_PARAM_CONSOLE_EVTCHN:
+    case HVM_PARAM_MONITOR_RING_PFN:
+        return d == current->domain ? -EPERM : 0;
+
+        /* Writeable only by Xen, hole, deprecated, or out-of-range. */
+    default:
+        return -EINVAL;
+    }
+}
+
+static int hvm_allow_get_param(const struct domain *d, unsigned int param)
+{
+    switch ( param )
+    {
+        /* The following parameters can be read by the guest and toolstack. */
+    case HVM_PARAM_CALLBACK_IRQ:
+    case HVM_PARAM_STORE_PFN:
+    case HVM_PARAM_STORE_EVTCHN:
+    case HVM_PARAM_CONSOLE_PFN:
+    case HVM_PARAM_CONSOLE_EVTCHN:
+        return 0;
+
+        /*
+         * The following parameters are intended for toolstack usage only.
+         * They may not be read by the domain.
+         */
+    case HVM_PARAM_MONITOR_RING_PFN:
+        return d == current->domain ? -EPERM : 0;
+
+        /* Hole, deprecated, or out-of-range. */
+    default:
+        return -EINVAL;
+    }
+}
+
 long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
     long rc = 0;
@@ -46,9 +97,6 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( copy_from_guest(&a, arg, 1) )
             return -EFAULT;
 
-        if ( a.index >= HVM_NR_PARAMS )
-            return -EINVAL;
-
         d = rcu_lock_domain_by_any_id(a.domid);
         if ( d == NULL )
             return -ESRCH;
@@ -59,10 +107,18 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
 
         if ( op == HVMOP_set_param )
         {
+            rc = hvm_allow_set_param(d, a.index);
+            if ( rc )
+                goto param_fail;
+
             d->arch.hvm.params[a.index] = a.value;
         }
         else
         {
+            rc = hvm_allow_get_param(d, a.index);
+            if ( rc )
+                goto param_fail;
+
             a.value = d->arch.hvm.params[a.index];
             rc = copy_to_guest(arg, &a, 1) ? -EFAULT : 0;
         }
-- 
2.11.0


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Re: [Xen-devel] [PATCH] xen/arm: Restrict access to most HVM_PARAM's
Posted by Julien Grall 5 years, 11 months ago 
Hi Andrew,

On 19/02/2020 19:30, Andrew Cooper wrote:
> ARM currently has no restrictions on toolstack and guest access to the entire
> HVM_PARAM block.  As the monitor feature isn't under security support, this
> doesn't need an XSA.
> 
> The CALLBACK_IRQ and {STORE,CONSOLE}_{PFN,EVTCHN} details are only exposed
> read-only to the guest, while MONITOR_RING_PFN is restricted to only toolstack
> access.  No other parameters are used.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Julien Grall <julien@xen.org>

Cheers,

> ---
> CC: Stefano Stabellini <sstabellini@kernel.org>
> CC: Julien Grall <julien@xen.org>
> CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
> 
> This is only compile tested, and based on my reading of the source.  There
> might be other PARAMS needing including.
> 
> v2:
>   * Drop paging/sharing
>   * Clarify comment about {STORE,CONSOLE}_EVTCHN
> ---
>   xen/arch/arm/hvm.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++---
>   1 file changed, 59 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/arch/arm/hvm.c b/xen/arch/arm/hvm.c
> index 76b27c9168..8951b34086 100644
> --- a/xen/arch/arm/hvm.c
> +++ b/xen/arch/arm/hvm.c
> @@ -31,6 +31,57 @@
>   
>   #include <asm/hypercall.h>
>   
> +static int hvm_allow_set_param(const struct domain *d, unsigned int param)
> +{
> +    switch ( param )
> +    {
> +        /*
> +         * The following parameters are intended for toolstack usage only.
> +         * They may not be set by the domain.
> +         *
> +         * The {STORE,CONSOLE}_EVTCHN values will need to become read/write to
> +         * the guest (not just the toolstack) if a new ABI hasn't appeared by
> +         * the time migration support is added.
> +         */
> +    case HVM_PARAM_CALLBACK_IRQ:
> +    case HVM_PARAM_STORE_PFN:
> +    case HVM_PARAM_STORE_EVTCHN:
> +    case HVM_PARAM_CONSOLE_PFN:
> +    case HVM_PARAM_CONSOLE_EVTCHN:
> +    case HVM_PARAM_MONITOR_RING_PFN:
> +        return d == current->domain ? -EPERM : 0;
> +
> +        /* Writeable only by Xen, hole, deprecated, or out-of-range. */
> +    default:
> +        return -EINVAL;
> +    }
> +}
> +
> +static int hvm_allow_get_param(const struct domain *d, unsigned int param)
> +{
> +    switch ( param )
> +    {
> +        /* The following parameters can be read by the guest and toolstack. */
> +    case HVM_PARAM_CALLBACK_IRQ:
> +    case HVM_PARAM_STORE_PFN:
> +    case HVM_PARAM_STORE_EVTCHN:
> +    case HVM_PARAM_CONSOLE_PFN:
> +    case HVM_PARAM_CONSOLE_EVTCHN:
> +        return 0;
> +
> +        /*
> +         * The following parameters are intended for toolstack usage only.
> +         * They may not be read by the domain.
> +         */
> +    case HVM_PARAM_MONITOR_RING_PFN:
> +        return d == current->domain ? -EPERM : 0;
> +
> +        /* Hole, deprecated, or out-of-range. */
> +    default:
> +        return -EINVAL;
> +    }
> +}
> +
>   long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
>   {
>       long rc = 0;
> @@ -46,9 +97,6 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
>           if ( copy_from_guest(&a, arg, 1) )
>               return -EFAULT;
>   
> -        if ( a.index >= HVM_NR_PARAMS )
> -            return -EINVAL;
> -
>           d = rcu_lock_domain_by_any_id(a.domid);
>           if ( d == NULL )
>               return -ESRCH;
> @@ -59,10 +107,18 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE_PARAM(void) arg)
>   
>           if ( op == HVMOP_set_param )
>           {
> +            rc = hvm_allow_set_param(d, a.index);
> +            if ( rc )
> +                goto param_fail;
> +
>               d->arch.hvm.params[a.index] = a.value;
>           }
>           else
>           {
> +            rc = hvm_allow_get_param(d, a.index);
> +            if ( rc )
> +                goto param_fail;
> +
>               a.value = d->arch.hvm.params[a.index];
>               rc = copy_to_guest(arg, &a, 1) ? -EFAULT : 0;
>           }
> 

-- 
Julien Grall

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