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XSA-216 Issue Description: > The block interface response structure has some discontiguous fields. > Certain backends populate the structure fields of an otherwise > uninitialized instance of this structure on their stacks, leaking > data through the (internal or trailing) padding field. More: https://xenbits.xen.org/xsa/advisory-216.html XSA-217 Issue Description: > Domains controlling other domains are permitted to map pages owned by > the domain being controlled. If the controlling domain unmaps such a > page without flushing the TLB, and if soon after the domain being > controlled transfers this page to another PV domain (via > GNTTABOP_transfer or, indirectly, XENMEM_exchange), and that third > domain uses the page as a page table, the controlling domain will have > write access to a live page table until the applicable TLB entry is > flushed or evicted. Note that the domain being controlled is > necessarily HVM, while the controlling domain is PV. More: https://xenbits.xen.org/xsa/advisory-217.html XSA-218 Issue Description: > We have discovered two bugs in the code unmapping grant references. > > * When a grant had been mapped twice by a backend domain, and then > unmapped by two concurrent unmap calls, the frontend may be informed > that the page had no further mappings when the first call completed rather > than when the second call completed. > > * A race triggerable by an unprivileged guest could cause a grant > maptrack entry for grants to be "freed" twice. The ultimate effect of > this would be for maptrack entries for a single domain to be re-used. More: https://xenbits.xen.org/xsa/advisory-218.html XSA-219 Issue Description: > When using shadow paging, writes to guest pagetables must be trapped and > emulated, so the shadows can be suitably adjusted as well. > > When emulating the write, Xen maps the guests pagetable(s) to make the final > adjustment and leave the guest's view of its state consistent. > > However, when mapping the frame, Xen drops the page reference before > performing the write. This is a race window where the underlying frame can > change ownership. > > One possible attack scenario is for the frame to change ownership and to be > inserted into a PV guest's pagetables. At that point, the emulated write will > be an unaudited modification to the PV pagetables whose value is under guest > control. More: https://xenbits.xen.org/xsa/advisory-219.html XSA-220 Issue Description: > Memory Protection Extensions (MPX) and Protection Key (PKU) are features in > newer processors, whose state is intended to be per-thread and context > switched along with all other XSAVE state. > > Xen's vCPU context switch code would save and restore the state only > if the guest had set the relevant XSTATE enable bits. However, > surprisingly, the use of these features is not dependent (PKU) or may > not be dependent (MPX) on having the relevant XSTATE bits enabled. > > VMs which use MPX or PKU, and context switch the state manually rather > than via XSAVE, will have the state leak between vCPUs (possibly, > between vCPUs in different guests). This in turn corrupts state in > the destination vCPU, and hence may lead to weakened protections > > Experimentally, MPX appears not to make any interaction with BND* > state if BNDCFGS.EN is set but XCR0.BND{CSR,REGS} are clear. However, > the SDM is not clear in this case; therefore MPX is included in this > advisory as a precaution. More: https://xenbits.xen.org/xsa/advisory-220.html XSA-221 Issue Description: > When polling event channels, in general arbitrary port numbers can be > specified. Specifically, there is no requirement that a polled event > channel ports has ever been created. When the code was generalised > from an earlier implementation, introducing some intermediate > pointers, a check should have been made that these intermediate > pointers are non-NULL. However, that check was omitted. More: https://xenbits.xen.org/xsa/advisory-221.html XSA-222 Issue Description: > Certain actions require removing pages from a guest's P2M > (Physical-to-Machine) mapping. When large pages are in use to map > guest pages in the 2nd-stage page tables, such a removal operation may > incur a memory allocation (to replace a large mapping with individual > smaller ones). If this allocation fails, these errors are ignored by > the callers, which would then continue and (for example) free the > referenced page for reuse. This leaves the guest with a mapping to a > page it shouldn't have access to. > > The allocation involved comes from a separate pool of memory created > when the domain is created; under normal operating conditions it never > fails, but a malicious guest may be able to engineer situations where > this pool is exhausted. More: https://xenbits.xen.org/xsa/advisory-222.html XSA-224 Issue Description: > We have discovered a number of bugs in the code mapping and unmapping > grant references. > > * If a grant is mapped with both the GNTMAP_device_map and > GNTMAP_host_map flags, but unmapped only with host_map, the device_map > portion remains but the page reference counts are lowered as though it > had been removed. This bug can be leveraged cause a page's reference > counts and type counts to fall to zero while retaining writeable > mappings to the page. > > * Under some specific conditions, if a grant is mapped with both the > GNTMAP_device_map and GNTMAP_host_map flags, the operation may not > grab sufficient type counts. When the grant is then unmapped, the > type count will be erroneously reduced. This bug can be leveraged > cause a page's reference counts and type counts to fall to zero while > retaining writeable mappings to the page. > > * When a grant reference is given to an MMIO region (as opposed to a > normal guest page), if the grant is mapped with only the > GNTMAP_device_map flag set, a mapping is created at host_addr anyway. > This does *not* cause reference counts to change, but there will be no > record of this mapping, so it will not be considered when reporting > whether the grant is still in use. More: https://xenbits.xen.org/xsa/advisory-224.html |
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