[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH 5/5] xen/ARM: Restrict access to most HVM_PARAM's


  • To: Julien Grall <julien.grall@xxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 6 Sep 2018 11:40:02 +0100
  • Autocrypt: addr=andrew.cooper3@xxxxxxxxxx; prefer-encrypt=mutual; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA==
  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Thu, 06 Sep 2018 10:40:10 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 06/09/18 11:36, Julien Grall wrote:
> Hi Paul,
>
> On 06/09/18 10:29, Paul Durrant wrote:
>>> -----Original Message-----
>>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
>>> Sent: 05 September 2018 19:12
>>> To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
>>> Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Jan Beulich
>>> <JBeulich@xxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Roger Pau Monne
>>> <roger.pau@xxxxxxxxxx>; Paul Durrant <Paul.Durrant@xxxxxxxxxx>; Stefano
>>> Stabellini <sstabellini@xxxxxxxxxx>; Julien Grall
>>> <julien.grall@xxxxxxx>
>>> Subject: [PATCH 5/5] xen/ARM: Restrict access to most HVM_PARAM's
>>>
>>> ARM currently has no restrictions on toolstack and guest access to
>>> the entire
>>> HVM_PARAM block.  As the paging/monitor/sharing features aren't under
>>> security
>>> support, this doesn't need an XSA.
>>>
>>> The CALLBACK_IRQ and {STORE,CONSOLE}_{PFN,EVTCHN} details exposed
>>> read-only to
>>> the guest, while the *_RING_PFN details are restricted to only
>>> toolstack
>>> access.  No other parameters are used.
>>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> ---
>>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>> CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
>>> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>> CC: Julien Grall <julien.grall@xxxxxxx>
>>>
>>> This is only compile tested, and based on my reading of the source. 
>>> There
>>> might be other PARAMS needing including.
>>> ---
>>>   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 76b27c9..3581ba2 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.
>>> +         */
>>> +    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:
>>
>> Probably should remove the EVTCHN params from this list after fixing
>> patch #3.
>>
>>> +    case HVM_PARAM_PAGING_RING_PFN:
>>> +    case HVM_PARAM_MONITOR_RING_PFN:
>>> +    case HVM_PARAM_SHARING_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_PAGING_RING_PFN:
>>> +    case HVM_PARAM_MONITOR_RING_PFN:
>>> +    case HVM_PARAM_SHARING_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;
>>> -
>>
>> ASSERT here.
>
> I don't think this would be correct. This is an input from the guest,
> so if you do fuzzing you will end up to get an hypervisor crash rather
> than returning an error.
>
> A potential place for an ASSERT would be just before accessing
> hvm.params. But then, technically the index should have been sanitized
> by hvm_allow_{get,set}_param.

Yeah - across all of these ASSERT() requests - using an assert for a
boundary check doesn't do anything in the case where it matters most,
and in this case, Julien is correct that it is a fully guest-controlled
number at this point.

~Andrew

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.