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

Re: [Xen-devel] [PATCH] fix BUG in gnttab_unpopulate_status_frames()


  • To: Jan Beulich <JBeulich@xxxxxxxx>, Paul Durrant <paul.durrant@xxxxxxxxxx>
  • From: George Dunlap <george.dunlap@xxxxxxxxxx>
  • Date: Fri, 2 Aug 2019 16:28:21 +0100
  • Authentication-results: esa5.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none; spf=None smtp.pra=george.dunlap@xxxxxxxxxx; spf=Pass smtp.mailfrom=George.Dunlap@xxxxxxxxxx; spf=None smtp.helo=postmaster@xxxxxxxxxxxxxxx
  • Autocrypt: addr=george.dunlap@xxxxxxxxxx; prefer-encrypt=mutual; keydata= mQINBFPqG+MBEACwPYTQpHepyshcufo0dVmqxDo917iWPslB8lauFxVf4WZtGvQSsKStHJSj 92Qkxp4CH2DwudI8qpVbnWCXsZxodDWac9c3PordLwz5/XL41LevEoM3NWRm5TNgJ3ckPA+J K5OfSK04QtmwSHFP3G/SXDJpGs+oDJgASta2AOl9vPV+t3xG6xyfa2NMGn9wmEvvVMD44Z7R W3RhZPn/NEZ5gaJhIUMgTChGwwWDOX0YPY19vcy5fT4bTIxvoZsLOkLSGoZb/jHIzkAAznug Q7PPeZJ1kXpbW9EHHaUHiCD9C87dMyty0N3TmWfp0VvBCaw32yFtM9jUgB7UVneoZUMUKeHA fgIXhJ7I7JFmw3J0PjGLxCLHf2Q5JOD8jeEXpdxugqF7B/fWYYmyIgwKutiGZeoPhl9c/7RE Bf6f9Qv4AtQoJwtLw6+5pDXsTD5q/GwhPjt7ohF7aQZTMMHhZuS52/izKhDzIufl6uiqUBge 0lqG+/ViLKwCkxHDREuSUTtfjRc9/AoAt2V2HOfgKORSCjFC1eI0+8UMxlfdq2z1AAchinU0 eSkRpX2An3CPEjgGFmu2Je4a/R/Kd6nGU8AFaE8ta0oq5BSFDRYdcKchw4TSxetkG6iUtqOO ZFS7VAdF00eqFJNQpi6IUQryhnrOByw+zSobqlOPUO7XC5fjnwARAQABtCRHZW9yZ2UgVy4g RHVubGFwIDxkdW5sYXBnQHVtaWNoLmVkdT6JAlcEEwEKAEECGwMFCwkIBwMFFQoJCAsFFgID AQACHgECF4ACGQEWIQTXqBy2bTNXPzpOYFimNjwxBZC0bQUCXEowWQUJDCJ7dgAKCRCmNjwx BZC0beKvEACJ75YlJXd7TnNHgFyiCJkm/qPeoQ3sFGSDZuZh7SKcdt9+3V2bFEb0Mii1hQaz 3hRqZb8sYPHJrGP0ljK09k3wf8k3OuNxziLQBJyzvn7WNlE4wBEcy/Ejo9TVBdA4ph5D0YaZ nqdsPmxe/xlTFuSkgu4ep1v9dfVP1TQR0e+JIBa/Ss+cKC5intKm+8JxpOploAHuzaPu0L/X FapzsIXqgT9eIQeBEgO2hge6h9Jov3WeED/vh8kA7f8c6zQ/gs5E7VGALwsiLrhr0LZFcKcw kI3oCCrB/C/wyPZv789Ra8EXbeRSJmTjcnBwHRPjnjwQmetRDD1t+VyrkC6uujT5jmgOBzaj KCqZ8PcMAssOzdzQtKmjUQ2b3ICPs2X13xZ5M5/OVs1W3TG5gkvMh4YoHi4ilFnOk+v3/j7q 65FG6N0JLb94Ndi80HkIOQQ1XVGTyu6bUPaBg3rWK91Csp1682kD/dNVF3FKHrRLmSVtmEQR 5rK0+VGc/FmR6vd4haKGWIRuPxzg+pBR77avIZpU7C7+UXGuZ5CbHwIdY8LojJg2TuUdqaVj yxmEZLOA8rVHipCGrslRNthVbJrGN/pqtKjCClFZHIAYJQ9EGLHXLG9Pj76opfjHij3MpR3o pCGAh6KsCrfrsvjnpDwqSbngGyEVH030irSk4SwIqZ7FwLkBDQRUWmc6AQgAzpc8Ng5Opbrh iZrn69Xr3js28p+b4a+0BOvC48NfrNovZw4eFeKIzmI/t6EkJkSqBIxobWRpBkwGweENsqnd 0qigmsDw4N7J9Xx0h9ARDqiWxX4jr7u9xauI+CRJ1rBNO3VV30QdACwQ4LqhR/WA+IjdhyMH wj3EJGE61NdP/h0zfaLYAbvEg47/TPThFsm4m8Rd6bX7RkrrOgBbL/AOnYOMEivyfZZKX1vv iEemAvLfdk2lZt7Vm6X/fbKbV8tPUuZELzNedJvTTBS3/l1FVz9OUcLDeWhGEdlxqXH0sYWh E9+PXTAfz5JxKH+LMetwEM8DbuOoDIpmIGZKrZ+2fQARAQABiQNbBBgBCgAmAhsCFiEE16gc tm0zVz86TmBYpjY8MQWQtG0FAlxKMJ4FCQnQ/OQBKcBdIAQZAQoABgUCVFpnOgAKCRCyFcen x4Qb7cXrCAC0qQeEWmLa9oEAPa+5U6wvG1t/mi22gZN6uzQXH1faIOoDehr7PPESE6tuR/vI CTTnaSrd4UDPNeqOqVF07YexWD1LDcQG6PnRqC5DIX1RGE3BaSaMl2pFJP8y+chews11yP8G DBbxaIsTcHZI1iVIC9XLhoeegWi84vYc8F4ziADVfowbmbvcVw11gE8tmALCwTeBeZVteXjh 0OELHwrc1/4j4yvENjIXRO+QLIgk43kB57Upr4tP2MEcs0odgPM+Q+oETOJ00xzLgkTnLPim C1FIW2bOZdTj+Uq6ezRS2LKsNmW+PRRvNyA5ojEbA/faxmAjMZtLdSSSeFK8y4SoCRCmNjwx BZC0bevWEACRu+GyQgrdGmorUptniIeO1jQlpTiP5WpVnk9Oe8SiLoXUhXXNj6EtzyLGpYmf kEAbki+S6WAKnzZd3shL58AuMyDxtFNNjNeKJOcl6FL7JPBIIgIp3wR401Ep+/s5pl3Nw8Ii 157f0T7o8CPb54w6S1WsMkU78WzTxIs/1lLblSMcvyz1Jq64g4OqiWI85JfkzPLlloVf1rzy ebIBLrrmjhCE2tL1RONpE/KRVb+Q+PIs5+YcZ+Q1e0vXWA7NhTWFbWx3+N6WW6gaGpbFbopo FkYRpj+2TA5cX5zW148/xU5/ATEb5vdUkFLUFVy5YNUSyeBHuaf6fGmBrDc47rQjAOt1rmyD 56MUBHpLUbvA6NkPezb7T6bQpupyzGRkMUmSwHiLyQNJQhVe+9NiJJvtEE3jol0JVJoQ9WVn FAzPNCgHQyvbsIF3gYkCYKI0w8EhEoH5FHYLoKS6Jg880IY5rXzoAEfPvLXegy6mhYl+mNVN QUBD4h9XtOvcdzR559lZuC0Ksy7Xqw3BMolmKsRO3gWKhXSna3zKl4UuheyZtubVWoNWP/bn vbyiYnLwuiKDfNAinEWERC8nPKlv3PkZw5d3t46F1Dx0TMf16NmP+azsRpnMZyzpY8BL2eur feSGAOB9qjZNyzbo5nEKHldKWCKE7Ye0EPEjECS1gjKDwbkBDQRUWrq9AQgA7aJ0i1pQSmUR 6ZXZD2YEDxia2ByR0uZoTS7N0NYv1OjU8v6p017u0Fco5+Qoju/fZ97ScHhp5xGVAk5kxZBF DT4ovJd0nIeSr3bbWwfNzGx1waztfdzXt6n3MBKr7AhioB1m+vuk31redUdnhbtvN7O40MC+ fgSk5/+jRGxY3IOVPooQKzUO7M51GoOg4wl9ia3H2EzOoGhN2vpTbT8qCcL92ZZZwkBRldoA Wn7c1hEKSTuT3f1VpSmhjnX0J4uvKZ1V2R7rooKJYFBcySC0wa8aTmAtAvLgfcpe+legOtgq DKzLuN45xzEjyjCiI521t8zxNMPJY9FiCPNv0sCkDwARAQABiQI8BBgBCgAmAhsMFiEE16gc tm0zVz86TmBYpjY8MQWQtG0FAlxKNJYFCQnQrVkACgkQpjY8MQWQtG2Xxg//RrRP+PFYuNXt 9C5hec/JoY24TkGPPd2tMC9usWZVImIk7VlHlAeqHeE0lWU0LRGIvOBITbS9izw6fOVQBvCA Fni56S12fKLusWgWhgu03toT9ZGxZ9W22yfw5uThSHQ4y09wRWAIYvhJsKnPGGC2KDxFvtz5 4pYYNe8Icy4bwsxcgbaSFaRh+mYtts6wE9VzyJvyfTqbe8VrvE+3InG5rrlNn51AO6M4Wv20 iFEgYanJXfhicl0WCQrHyTLfdB5p1w+072CL8uryHQVfD0FcDe+J/wl3bmYze+aD1SlPzFoI MaSIXKejC6oh6DAT4rvU8kMAbX90T834Mvbc3jplaWorNJEwjAH/r+v877AI9Vsmptis+rni JwUissjRbcdlkKBisoUZRPmxQeUifxUpqgulZcYwbEC/a49+WvbaYUriaDLHzg9xisijHwD2 yWV8igBeg+cmwnk0mPz8tIVvwi4lICAgXob7HZiaqKnwaDXs4LiS4vdG5s/ElnE3rIc87yru 24n3ypeDZ6f5LkdqL1UNp5/0Aqbr3EiN7/ina4YVyscy9754l944kyHnnMRLVykg0v+kakj0 h0RJ5LbfLAMM8M52KIA3y14g0Fb7kHLcOUMVcgfQ3PrN6chtC+5l6ouDIlSLR3toxH8Aam7E rIFfe2Dk+lD9A9BVd2rfoHA=
  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, TimDeegan <tim@xxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Fri, 02 Aug 2019 15:28:42 +0000
  • Ironport-sdr: CZYp74rKhBYBO7p6Qf0V405XxCBsdIqbc6+CsQMwYWptWnwXvrMjEsjZZj/t63UgVANbdDiArD jJdYdyLaiW+wWOXS6hkGBNyT/RlIMxt9Jjz0HFTVM6aMW3iULIqg44u+4DZu0auak95ZjemU4N yZ2m6cZk5NHcWTaQ4blPy4RRskRj5O26wB8F46MZS7e6AW1jeMh9Fy8WxLu3R1+Vt7hGdNyf76 y3grInUcY0rRP5UBFfVCtT4x2RE06xk4f+K4IqaktIuNeNnLx/gaQVxrcP7LYDBTGSKHJyv8NV d4s=
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 8/2/19 3:44 PM, Jan Beulich wrote:
> On 30.07.2019 18:44, Paul Durrant wrote:
>> --- a/xen/common/grant_table.c
>> +++ b/xen/common/grant_table.c
>> @@ -1682,6 +1682,14 @@ gnttab_unpopulate_status_frames(struct domain *d, 
>> struct grant_table *gt)
>>           struct page_info *pg = virt_to_page(gt->status[i]);
>>           gfn_t gfn = gnttab_get_frame_gfn(gt, true, i);
>>   
>> +        if ( !get_page(pg, d) )
>> +        {
>> +            gprintk(XENLOG_ERR,
>> +                    "Could not get a reference to status frame %u\n", i);
>> +            domain_crash(d);
>> +            return -EINVAL;
>> +        }
>> +
>>           /*
>>            * For translated domains, recovering from failure after partial
>>            * changes were made is more complicated than it seems worth
>> @@ -1708,6 +1716,7 @@ gnttab_unpopulate_status_frames(struct domain *d, 
>> struct grant_table *gt)
>>   
>>           BUG_ON(page_get_owner(pg) != d);
>>           put_page_alloc_ref(pg);
>> +        put_page(pg);
>>   
>>           if ( pg->count_info & ~PGC_xen_heap )
>>           {
>>
> 
> I dislike this approach, and not chosing the alternative of excluding
> xenheap pages in the check in put_page_alloc_ref() (as I had recommended
> elsewhere) should at least be discussed in the description. It is the
> very nature of xenheap pages that they won't get freed, and hence don't
> need this extra ref to be held for clearing PGC_allocated.

Also, it looks like there are other places where the BUG_ON() may /
should be firing:  namely, vmx_free_vlapic_mapping() and
unshare_xenoprof_page_with_guest().  Teaching put_page_alloc_ref() that
dropping PGC_allocated when PGC_xen_heap is set is safe would fix all
three at once.

Possibly more importantly, suppose that the first time
gnttab_unpopulate_status_frames() comes around, gt->status[1] is still
mapped by the guest.  Then gt->status[0] will have its refcount reduced
to 0 (but not freed), but gt->status[1] will be restored to its previous
state.  If the guest unmaps gt->status[1] and
gnttab_unpopulate_status_frames() is called again, then the
get_page(gt->status[0]) will fail (since its refcount is 0), causing the
guest to be crashed instead.

Not terrible for such a wonkily-behaving guest; but I think I'd rather
go with the "special-case xenheap pages" option.

 -George


_______________________________________________
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®.