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
XSA-206 Issue Description:
> xenstored supports transactions, such that if writes which would
> invalidate assumptions of a transaction occur, the entire transaction
> fails. Typical response on a failed transaction is to simply retry
> the transaction until it succeeds.
>
> Unprivileged domains may issue writes to xenstore which conflict with
> transactions either of the toolstack or of backends such as the driver
> domain. Depending on the exact timing, repeated writes may cause
> transactions made by these entities to fail indefinitely.
More: https://xenbits.xen.org/xsa/advisory-206.html
XSA-211 Issue Description:
> When a graphics update command gets passed to the VGA emulator, there
> are 3 possible modes that can be used to update the display:
>
> * blank - Clears the display
> * text - Treats the display as showing text
> * graph - Treats the display as showing graphics
>
> After the display geometry gets changed (i.e., after the CIRRUS VGA
> emulation has resized the display), the VGA emulator will resize the
> console during the next update command. However, when a blank mode is
> also selected during an update, this resize doesn't happen. The resize
> will be properly handled during the next time a non-blank mode is
> selected during an update.
>
> However, other console components - such as the VNC emulation - will
> operate as though this resize had happened. When the display is
> resized to be larger than before, this can result in a heap overflow
> as console components will expect the display buffer to be larger than
> it is currently allocated.
More: https://xenbits.xen.org/xsa/advisory-211.html
XSA-212 Issue Description:
> The XSA-29 fix introduced an insufficient check on XENMEM_exchange
> input, allowing the caller to drive hypervisor memory accesses outside
> of the guest provided input/output arrays.
More: https://xenbits.xen.org/xsa/advisory-212.html
XSA-213 Issue Description:
> 64-bit PV guests typically use separate (root) page tables for their
> kernel and user modes. Hypercalls are accessible to guest kernel
> context only, which certain hypercall handlers make assumptions on.
> The IRET hypercall (replacing the identically name CPU instruction)
> is used by guest kernels to transfer control from kernel mode to user
> mode. If such an IRET hypercall is placed in the middle of a multicall
> batch, subsequent operations invoked by the same multicall batch may
> wrongly assume the guest to still be in kernel mode. If one or more of
> these subsequent operations involve operations on page tables, they may
> be using the wrong root page table, confusing internal accounting. As
> a result the guest may gain writable access to some of its page tables.
More: https://xenbits.xen.org/xsa/advisory-213.html
XSA-214 Issue Description:
> The GNTTABOP_transfer operation allows one guest to transfer a page to
> another guest. The internal processing of this, however, does not
> include zapping the previous type of the page being transferred. This
> makes it possible for a PV guest to transfer a page previously used as
> part of a segment descriptor table to another guest while retaining the
> "contains segment descriptors" property.
>
> If the destination guest is a PV one of different bitness, it may gain
> access to segment descriptors it is not normally allowed to have, like
> 64-bit code segments in a 32-bit PV guest.
>
> If the destination guest is a HVM one, that guest may freely alter the
> page contents and then hand the page back to the same or another PV
> guest.
>
> In either case, if the destination PV guest then inserts that page into
> one of its own descriptor tables, the page still having the designated
> type results in validation of its contents being skipped.
More: https://xenbits.xen.org/xsa/advisory-214.html
XSA-215 Issue Description:
> Under certain special conditions Xen reports an exception resulting
> from returning to guest mode not via ordinary exception entry points,
> but via a so call failsafe callback. This callback, unlike exception
> handlers, takes 4 extra arguments on the stack (the saved data
> selectors DS, ES, FS, and GS). Prior to placing exception or failsafe
> callback frames on the guest kernel stack, Xen checks the linear
> address range to not overlap with hypervisor space. The range spanned
> by that check was mistakenly not covering these extra 4 slots.
More: https://xenbits.xen.org/xsa/advisory-215.html
OVMF{,CODE,VARS}.fd are now available in a dedicated fd output, greatly
reducing the closure in the common case where only those files are used (a
few MBs versus several hundred MBs for the full OVMF).
Note: it's unclear why `dontPatchELF` is now necessary for the build to
pass (on my end, at any rate) but it doesn't make much sense to run this
fixup anyway,
Note: my reading of xen's INSTALL suggests that --with-system-ovmf should
point directly to the OVMF binary. As such, the previous invocation was
incorrect (it pointed to the root of the OVMF tree). In any case, I have
only built xen with `--with-system-ovmf`, I have not tested it.
Fixes https://github.com/NixOS/nixpkgs/issues/25854
Closes https://github.com/NixOS/nixpkgs/pull/25855
Also:
* provides a bunch of build options
* documents build options config in longDescription
* provides a bunch of predefined packages and documents them some more
* sources' hashes stay the same
XSA-197 Issue Description:
> The compiler can emit optimizations in qemu which can lead to double
> fetch vulnerabilities. Specifically data on the rings shared
> between qemu and the hypervisor (which the guest under control can
> obtain mappings of) can be fetched twice (during which time the
> guest can alter the contents) possibly leading to arbitrary code
> execution in qemu.
More: https://xenbits.xen.org/xsa/advisory-197.html
XSA-199 Issue Description:
> The code in qemu which implements ioport read/write looks up the
> specified ioport address in a dispatch table. The argument to the
> dispatch function is a uint32_t, and is used without a range check,
> even though the table has entries for only 2^16 ioports.
>
> When qemu is used as a standalone emulator, ioport accesses are
> generated only from cpu instructions emulated by qemu, and are
> therefore necessarily 16-bit, so there is no vulnerability.
>
> When qemu is used as a device model within Xen, io requests are
> generated by the hypervisor and read by qemu from a shared ring. The
> entries in this ring use a common structure, including a 64-bit
> address field, for various accesses, including ioport addresses.
>
> Xen will write only 16-bit address ioport accesses. However,
> depending on the Xen and qemu version, the ring may be writeable by
> the guest. If so, the guest can generate out-of-range ioport
> accesses, resulting in wild pointer accesses within qemu.
More: https://xenbits.xen.org/xsa/advisory-199.html
XSA-207 Issue Description:
> Certain internal state is set up, during domain construction, in
> preparation for possible pass-through device assignment. On ARM and
> AMD V-i hardware this setup includes memory allocation. On guest
> teardown, cleanup was erroneously only performed when the guest
> actually had a pass-through device assigned.
More: https://xenbits.xen.org/xsa/advisory-207.html
XSA-209 Issue Description:
> When doing bitblt copy backwards, qemu should negate the blit width.
> This avoids an oob access before the start of video memory.
More: https://xenbits.xen.org/xsa/advisory-208.html
XSA-208 Issue Description:
> In CIRRUS_BLTMODE_MEMSYSSRC mode the bitblit copy routine
> cirrus_bitblt_cputovideo fails to check wethehr the specified memory
> region is safe.
More: https://xenbits.xen.org/xsa/advisory-209.html
