linux/arch/x86/include/asm/xen
David Vrabel 0160676bba xen/p2m: check MFN is in range before using the m2p table
On hosts with more than 168 GB of memory, a 32-bit guest may attempt
to grant map an MFN that is error cannot lookup in its mapping of the
m2p table.  There is an m2p lookup as part of m2p_add_override() and
m2p_remove_override().  The lookup falls off the end of the mapped
portion of the m2p and (because the mapping is at the highest virtual
address) wraps around and the lookup causes a fault on what appears to
be a user space address.

do_page_fault() (thinking it's a fault to a userspace address), tries
to lock mm->mmap_sem.  If the gntdev device is used for the grant map,
m2p_add_override() is called from from gnttab_mmap() with mm->mmap_sem
already locked.  do_page_fault() then deadlocks.

The deadlock would most commonly occur when a 64-bit guest is started
and xenconsoled attempts to grant map its console ring.

Introduce mfn_to_pfn_no_overrides() which checks the MFN is within the
mapped portion of the m2p table before accessing the table and use
this in m2p_add_override(), m2p_remove_override(), and mfn_to_pfn()
(which already had the correct range check).

All faults caused by accessing the non-existant parts of the m2p are
thus within the kernel address space and exception_fixup() is called
without trying to lock mm->mmap_sem.

This means that for MFNs that are outside the mapped range of the m2p
then mfn_to_pfn() will always look in the m2p overrides.  This is
correct because it must be a foreign MFN (and the PFN in the m2p in
this case is only relevant for the other domain).

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@citrix.com>
Cc: Jan Beulich <JBeulich@suse.com>
--
v3: check for auto_translated_physmap in mfn_to_pfn_no_overrides()
v2: in mfn_to_pfn() look in m2p_overrides if the MFN is out of
    range as it's probably foreign.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
2013-09-25 09:00:03 -04:00
..
events.h xen: Support 64-bit PV guest receiving NMIs 2013-08-09 10:55:47 -04:00
hypercall.h xen-pciback: notify hypervisor about devices intended to be assigned to guests 2013-03-22 10:20:55 -04:00
hypervisor.h x86: remove obsolete comment from asm/xen/hypervisor.h 2012-10-30 09:27:32 -04:00
interface_32.h xen: implement XENMEM_machphys_mapping 2010-11-12 15:00:06 -08:00
interface_64.h xen: implement XENMEM_machphys_mapping 2010-11-12 15:00:06 -08:00
interface.h xen: arm: implement remap interfaces needed for privcmd mappings. 2012-11-29 14:00:19 +00:00
page.h xen/p2m: check MFN is in range before using the m2p table 2013-09-25 09:00:03 -04:00
pci.h xen/pci: Squash pci_xen_initial_domain and xen_setup_pirqs together. 2011-07-11 13:19:30 -04:00
swiotlb-xen.h xen/swiotlb: Use the swiotlb_late_init_with_tbl to init Xen-SWIOTLB late when PV PCI is used. 2012-09-17 12:58:16 -04:00
trace_types.h xen/trace: add multicall tracing 2011-07-18 15:43:26 -07:00