The latest oxenstored from Xapi-project fails to start up:
launch-xenstore[1201]: Starting /usr/sbin/oxenstored...
launch-xenstore[1222]: Fatal error: exception
Dynlink.Error (Dynlink.Cannot_open_dll "Dynlink.Error (Dynlink.Cannot_open_dll
\"Failure(\\\"/usr/libexec/xen//ocaml/xsd_glue/xenctrl_plugin/domain_getinfo_v1.cmxs:
undefined symbol: xc_domain_getinfo_single\\\")\")")
This is because domain_getinfo_v1.cmxs isn't dynamically linked correctly.
Fill in the correct variable, and remove the xen prefix from xenctrl.
Reported-by: Edwin Török <edwin.torok@citrix.com>
Suggested-by: Edwin Török <edwin.torok@citrix.com>
Fixes: a6576011a4 ("ocaml/libs: Implement a dynamically-loaded plugin for Xenctrl.domain_getinfo")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Release-Acked-By: Oleksii Kurochko <oleksii.kurochko@gmail.com>
(cherry picked from commit 343e01fd1d)
... which uses XENVER_extraversion2.
In order to do this sensibly, use manual hypercall buffer handling. Not only
does this avoid an extra bounce buffer (we need to strip the xen_varbuf_t
header anyway), it's also shorter and easlier to follow.
Update libxl and the ocaml stubs to match. No API/ABI change in either.
With this change made, `xl info` can now correctly access a >15 char
extraversion:
# xl info xen_version
4.18-unstable+REALLY LONG EXTRAVERSION
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
On Fedora 40, the build fails with:
In file included from domain_getinfo_stubs_v1.c:10:
domain_getinfo_stubs_v1.c: In function 'xsd_glue_failwith':
/usr/lib64/ocaml/caml/memory.h:275:29: error: unused variable 'caml__frame' [-Werror=unused-variable]
275 | struct caml__roots_block *caml__frame = *caml_local_roots_ptr
| ^~~~~~~~~~~
domain_getinfo_stubs_v1.c:48:9: note: in expansion of macro 'CAMLparam0'
48 | CAMLparam0();
| ^~~~~~~~~~
cc1: all warnings being treated as errors
The CAMLparam0 macro is defined in /usr/lib64/ocaml/caml/memory.h:255 as:
#define CAMLparam0() \
struct caml__roots_block** caml_local_roots_ptr = \
(DO_CHECK_CAML_STATE ? Caml_check_caml_state() : (void)0, \
&CAML_LOCAL_ROOTS); \
struct caml__roots_block *caml__frame = *caml_local_roots_ptr
We can't modify the macro. But, it turns out there's a CAMLnoreturn macro
with the sole purpose of masking this warning.
Fixes: a6576011a4 ("ocaml/libs: Implement a dynamically-loaded plugin for Xenctrl.domain_getinfo")
Signed-off-by: Javi Merino <javi.merino@cloud.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
xsd_glue_dev packaging is inconsistent with the rest of OCaml packages and
isn't actually necessary. The .a is needed alongside compiled bytecode files
during linking and was missed in the initial oxenstored plugin work.
Specify OCAMLCFLAGS along with OCAMLOPTFLAGS.
Signed-off-by: Andrii Sultanov <andrii.sultanov@cloud.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
This plugin intends to hide the unstable Xenctrl interface under a
stable one. In case of the change in the interface, a V2 of this plugin
would need to be produced, but V1 with the old interface would
need to be kept (with potential change in the implementation) in the
meantime.
To reduce the need for such changes in the future, this plugin only
provides the absolute minimum functionality that Oxenstored uses - only
three fields of the domaininfo struct are used and presented here.
Oxenstored currently uses the single-domain domain_getinfo function,
whereas domain_getinfolist is a potentially more efficient option. Both
of these are provided in the plugin to allow a transition from one to
the other without modifying the interface in the future. Both return
identical structures and rely on the same fields in xenctrl, thus if one
of them breaks, both will break, and a new version of the interface
would need to be issued.
Signed-off-by: Andrii Sultanov <andrii.sultanov@cloud.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
The root .gitignore is quite stale from recent (and less recent) removals, but
also fails to work for the forthcoming dynamic plugin work.
Strip all Ocaml content out of the root .gitignore, and provide a more local
.gitignore's with up-to-date patterns.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Enabling it using an HVM param is fragile, and complicates the logic when
deciding whether options that interact with altp2m can also be enabled.
Leave the HVM param value for consumption by the guest, but prevent it from
being set. Enabling is now done using and additional altp2m specific field in
xen_domctl_createdomain.
Note that albeit only currently implemented in x86, altp2m could be implemented
in other architectures, hence why the field is added to xen_domctl_createdomain
instead of xen_arch_domainconfig.
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com> # hypervisor
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com> # tools/libs/
Release-acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Add the missing `vmtrace_buf_kb` field to the OCaml bindings to match the
vm.cfg configuration, correcting an oversight from its initial introduction.
Signed-off-by: Petr Beneš <w1benny@gmail.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
`Tag_cons` is `0` and is meant to be used as the tag argument for
`caml_alloc`/`caml_alloc_small` when constructing a non-empty list.
The empty list is `Val_emptylist` instead, which is really just `Val_int(0)`.
Assigning `0` to a list value like this is equivalent to assigning the naked
pointer `NULL` to the field. Naked pointers are not valid in OCaml 5, however
even in OCaml <5.x any attempt to iterate on the list will lead to a segfault.
The list currently only has an opaque type, so no code would have reason to
iterate on it currently, but we shouldn't construct invalid OCaml values that
might lead to a crash when exploring the type.
`Val_emptylist` is available since OCaml 3.01 as a constant.
Fixes: e5ac68a011 ("x86/hvm: Revert per-domain APIC acceleration support")
Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
The original change doesn't compile on ARM:
xenctrl_stubs.c: In function 'stub_xc_physinfo':
xenctrl_stubs.c:821:16: error: unused variable 'arch_cap_flags_tag' [-Werror=unused-variable]
821 | int r, arch_cap_flags_tag;
| ^~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
but it was buggy too.
First, it tried storing an int in a pointer slot, causing heap corruption.
Next, it is not legitimate to exclude arm32 in the toolstack as it explicitly
can operate an arm64 toolstack and build arm64 domains. That in turn means
that you can't stash a C uint32_t in an OCaml int.
Rewrite the arch_capabilities handling from scratch. Break it out into a
separate function, and make the construction of arch_physinfo_cap_flags common
to prevent other indirection bugs.
Reintroduce arm_physinfo_caps with the fields broken out.
Fixes: 56a7aaa16b ("tools: add physinfo arch_capabilities handling for Arm")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
On Arm, the SVE vector length is encoded in arch_capabilities field
of struct xen_sysctl_physinfo, make use of this field in the tools
when building for arm.
Create header arm-arch-capabilities.h to handle the arch_capabilities
field of physinfo for Arm.
Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
xc_domain_getinfolist() internally relies on a sysctl that performs
a linear search for the domids. Many callers of xc_domain_getinfolist()
who require information about a precise domid are much better off calling
xc_domain_getinfo_single() instead, that will use the getdomaininfo domctl
instead and ensure the returned domid matches the requested one. The domtctl
will find the domid faster too, because that uses hashed lists.
Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Strings in Ocaml carry their own length. Absolutely nothing good can come
from having caml_string_length(data) be different to len.
Use the appropriate accessor, String_val(), but retain the workaround for the
Ocaml -safe-string constness bug in the same way as we've done elsewhere in
Xen.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
In order to better reflect the contents of the header and to make it
more appropriate to use it for different runtime environments like
programs, libraries, and firmware, rename the libs.h include file to
common-macros.h. Additionally add a comment pointing out the need to be
self-contained.
Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> # tools/python/xen/lowlevel/xc/xc.c
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Featuresets are supposed to be disappearing when the CPU policy infrastructure
is complete, but that has taken longer than expected, and isn't going to be
complete imminently either.
In the meantime, Xen does have proper default/max featuresets, and xen-cpuid
can even get them via the XEN_SYSCTL_cpu_policy_* interface, but only knows
now to render them nicely via the featureset interface.
Differences between default and max are a frequent source of errors,
frequently too in secret leading up to an embargo, so extend the featureset
sysctl to allow xen-cpuid to render them all nicely.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
All caml_alloc_*() functions can throw exceptions, and longjump out of
context. If this happens, we leak the xch/xce handle.
Reorder the logic to allocate the the Ocaml object first.
Fixes: 8b3c06a3e5 ("tools/ocaml/xenctrl: OCaml 5 support, fix use-after-free")
Fixes: 22d5affdf0 ("tools/ocaml/evtchn: OCaml 5 support, fix potential resource leak")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
The modification to the _H() macro for Ocaml 5 support introduced a subtle
bug. From the manual:
https://ocaml.org/manual/intfc.html#ss:parallel-execution-long-running-c-code
"After caml_release_runtime_system() was called and until
caml_acquire_runtime_system() is called, the C code must not access any OCaml
data, nor call any function of the run-time system, nor call back into OCaml
code."
Previously, the value was a naked C pointer, so dereferencing it wasn't
"accessing any Ocaml data", but the fix to avoid naked C pointers added a
layer of indirection through an Ocaml Custom object, meaning that the common
pattern of using _H() in a blocking section is unsafe.
In order to fix:
* Drop the _H() macro and replace it with a static inline xch_of_val().
* Opencode the assignment into Data_custom_val() in the constructors.
* Rename "value xch" parameters to "value xch_val" so we can consistently
have "xc_interface *xch" on the stack, and obtain the pointer with the GC
lock still held.
* Drop the _D() macro while at it, because it's just pointless indirection.
Fixes: 8b3c06a3e5 ("tools/ocaml/xenctrl: OCaml 5 support, fix use-after-free")
Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
The intf->{addr,len} references in the xc_map_foreign_range() call are unsafe.
From the manual:
https://ocaml.org/manual/intfc.html#ss:parallel-execution-long-running-c-code
"After caml_release_runtime_system() was called and until
caml_acquire_runtime_system() is called, the C code must not access any OCaml
data, nor call any function of the run-time system, nor call back into OCaml
code."
More than what the manual says, the intf pointer is (potentially) invalidated
by caml_enter_blocking_section() if another thread happens to perform garbage
collection at just the right (wrong) moment.
Rewrite the logic. There's no need to stash data in the Ocaml object until
the success path at the very end.
Fixes: 8b7ce06a2d ("ocaml: Add XC bindings.")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
The patch adding this binding was plain broken, and unreviewed. It modified
the C stub to add a 4th parameter without an equivalent adjustment in the
Ocaml side of the bindings.
In 64bit builds, this causes us to dereference whatever dead value is in %rcx
when trying to interpret the rflags parameter.
This has gone unnoticed because Xapi doesn't use this binding (it has its
own), but unbreak the binding by passing RDM_RELAXED unconditionally for
now (matching the libxl default behaviour).
Fixes: 9b34056cb4 ("tools: extend xc_assign_device() to support rdm reservation policy")
Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
* Remove local integers when all we're returning is Val_int() of another
variable. The CAMLlocal*() can't be optimised automatically, as it's
registered with the GC.
* Rename "virq_type" to "virq" and "_port" to "port".
* In stub_eventchn_pending(), rename 'port' to 'rc', to be consistent with
all other stubs that return xenevtchn_port_or_error_t.
* In stub_eventchn_unmask(), check for rc == -1 to be consistent with all
other stubs.
No practical change.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
The modification to the _H() macro for Ocaml 5 support introduced a subtle
bug. From the manual:
https://ocaml.org/manual/intfc.html#ss:parallel-execution-long-running-c-code
"After caml_release_runtime_system() was called and until
caml_acquire_runtime_system() is called, the C code must not access any OCaml
data, nor call any function of the run-time system, nor call back into OCaml
code."
Previously, the value was a naked C pointer, so dereferencing it wasn't
"accessing any Ocaml data", but the fix to avoid naked C pointers added a
layer of indirection through an Ocaml Custom object, meaning that the common
pattern of using _H() in a blocking section is unsafe.
In order to fix:
* Drop the _H() macro and replace it with a static inline xce_of_val().
* Opencode the assignment into Data_custom_val() in the two constructors.
* Rename "value xce" parameters to "value xce_val" so we can consistently
have "xenevtchn_handle *xce" on the stack, and obtain the pointer with the
GC lock still held.
Fixes: 22d5affdf0 ("tools/ocaml/evtchn: OCaml 5 support, fix potential resource leak")
Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
caml_alloc() takes units of Wsize (word size), not bytes. As a consequence,
we're allocating 4 or 8 times too much memory.
Ocaml has a helper, Wsize_bsize(), but it truncates cases which aren't an
exact multiple. Use a BUILD_BUG_ON() to cover the potential for truncation,
as there's no rounding-up form of the helper.
Fixes: 8b7ce06a2d ("ocaml: Add XC bindings.")
Fixes: d3e649277a ("ocaml: add mmap bindings implementation.")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
There is no such thing as an Ocaml function (C stub or otherwise) taking no
parameters. In the absence of any other parameters, unit is still passed.
This doesn't explode with any ABI we care about, but would malfunction for an
ABI environment such as stdcall.
Fixes: c3afd398ba ("ocaml: Add XS bindings.")
Fixes: 8b7ce06a2d ("ocaml: Add XC bindings.")
Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
This function is unusued (only Xs_ring.write_substring is used), and the
bytes/string conversion here is backwards: the C stub implements the bytes
version and then we use a Bytes.unsafe_of_string to convert a string into
bytes.
However the operation here really is read-only: we read from the string and
write it to the ring, so the C stub should implement the read-only string
version, and if needed we could use Bytes.unsafe_to_string to be able to send
'bytes'. However that is not necessary as the 'bytes' version is dropped above.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
This is not strictly necessary since it is essentially a no-op currently: a
cast to void * and value *, even in OCaml 5.0.
However it does make it clearer that what we have here is not a regular OCaml
value, but one allocated with Abstract_tag or Custom_tag, and follows the
example from the manual more closely:
https://v2.ocaml.org/manual/intfc.html#ss:c-outside-head
It also makes it clearer that these modules have been reviewed for
compat with OCaml 5.0.
We cannot use OCaml finalizers here, because we want exact control over when
to unmap these pages from remote domains.
No functional change.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Not to be confused which hvm_get_param, which also exists and has a
different, more error-prone interface.
This one always returns a 64-bit value, and that is retained in the
OCaml binding as well, returning 'int64' (and not int, or nativeint
which might have different sizes).
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
There is no API or ioctl to query event channel status, it is only
present in xenctrl.h
The C union is mapped to an OCaml variant exposing just the value from
the correct union tag. This causes the xc bindings to now depend on
evtchn to get a useful API for EVTCHNSTAT_virq.
The information provided here is similar to 'lsevtchn', but rather than
parsing its output it queries the underlying API directly.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
The binding for xc_interface_close() free the underlying handle while leaving
the Ocaml object still in scope and usable. This would make it easy to suffer
a use-after-free, if it weren't for the fact that the typical usage is as a
singleton that lives for the lifetime of the program.
Ocaml 5 no longer permits storing a naked C pointer in an Ocaml value.
Therefore, use a Custom block. This allows us to use the finaliser callback
to call xc_interface_close(), if the Ocaml object goes out of scope.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
For live update, oxenstored wants to clear CLOEXEC on the evtchn handle, so it
survives the execve() into the new oxenstored.
Have the new interface match how cloexec works in other Ocaml standard
libraries.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
There is no binding for xenevtchn_close(). In principle, this is a resource
leak, but the typical usage is as a singleton that lives for the lifetime of
the program.
Ocaml 5 no longer permits storing a naked C pointer in an Ocaml value.
Therefore, use a Custom block. This allows us to use the finaliser callback
to call xenevtchn_close(), if the Ocaml object goes out of scope.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
domain_getinfolist() is quadratic with the number of domains, because of the
behaviour of the underlying hypercall. Nevertheless, getting domain info in
blocks of 1024 is far more efficient than blocks of 2.
In a scalability testing scenario with ~1000 VMs, a combination of this and
the previous change takes xenopsd's wallclock time in domain_getinfolist()
down from 88% to 0.02%
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Tested-by: Pau Ruiz Safont <pau.safont@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
domain_getinfolist() is quadratic with the number of domains, because of the
behaviour of the underlying hypercall. xenopsd was further observed to be
wasting excessive quantites of time manipulating the list of already-obtained
domains.
Implement a tail recursive `rev_concat` equivalent to `concat |> rev`, and use
it instead of calling `@` multiple times.
An incidental benefit is that the list of domains will now be in domid order,
instead of having pairs of 2 domains changing direction every time.
In a scalability testing scenario with ~1000 VMs, a combination of this and
the subsequent change takes xenopsd's wallclock time in domain_getinfolist()
down from 88% to 0.02%
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Tested-by: Pau Ruiz Safont <pau.safont@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
I was really hoping to avoid this, but its now too late in the 4.17 freeze and
we still don't have working fixes.
The in-Xen calculations for assistance capabilities are buggy. For the
avoidance of doubt, the original intention was to be able to control every
aspect of a APIC acceleration so we could comprehensively test Xen's support,
as it has proved to be buggy time and time again.
Even after a protracted discussion on what the new API ought to mean, attempts
to apply it to the existing logic have been unsuccessful, proving that the
API/ABI is too complicated for most people to reason about.
This reverts most of:
2ce11ce2496b2b9b3405
leaving in place the non-APIC specific changes (minimal as they are).
This takes us back to the behaviour of Xen 4.16 where APIC acceleration is
configured on a per system basis.
This work will be revisted in due course.
Fixes: 2ce11ce249 ("x86/HVM: allow per-domain usage of hardware virtualized APIC")
Fixes: 6b2b9b3405 ("x86: report Interrupt Controller Virtualization capabilities")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>
Integers in Ocaml have 63 or 31 bits of signed precision.
On 64-bit builds of Ocaml, this is fine because a C uint32_t always fits
within a 63-bit signed integer.
In 32-bit builds of Ocaml, this goes wrong. The C uint32_t is truncated
first (loses the top bit), then has a unsigned/signed mismatch.
A "negative" value (i.e. a packet on the ring of between 1G and 2G in size)
will trigger an exception later in Bytes.make in xb.ml, and because the packet
is not removed from the ring, the exception re-triggers on every subsequent
query, creating a livelock.
Fix both the source of the exception in Xb, and as defence in depth, mark the
domain as bad for any Invalid_argument exceptions to avoid the risk of
livelock.
This is XSA-420 / CVE-2022-42324.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Introduce a limit on the number of outstanding reply packets in the xenbus
queue. This limits the number of in-flight requests: when the output queue is
full we'll stop processing inputs until the output queue has room again.
To avoid a busy loop on the Unix socket we only add it to the watched input
file descriptor set if we'd be able to call `input` on it. Even though Dom0
is trusted and exempt from quotas a flood of events might cause a backlog
where events are produced faster than daemons in Dom0 can consume them, which
could lead to an unbounded queue size and OOM.
Therefore the xenbus queue limit must apply to all connections, Dom0 is not
exempt from it, although if everything works correctly it will eventually
catch up.
This prevents a malicious guest from sending more commands while it has
outstanding watch events or command replies in its input ring. However if it
can cause the generation of watch events by other means (e.g. by Dom0, or
another cooperative guest) and stop reading its own ring then watch events
would've queued up without limit.
The xenstore protocol doesn't have a back-pressure mechanism, and doesn't
allow dropping watch events. In fact, dropping watch events is known to break
some pieces of normal functionality. This leaves little choice to safely
implement the xenstore protocol without exposing the xenstore daemon to
out-of-memory attacks.
Implement the fix as pipes with bounded buffers:
* Use a bounded buffer for watch events
* The watch structure will have a bounded receiving pipe of watch events
* The source will have an "overflow" pipe of pending watch events it couldn't
deliver
Items are queued up on one end and are sent as far along the pipe as possible:
source domain -> watch -> xenbus of target -> xenstore ring/socket of target
If the pipe is "full" at any point then back-pressure is applied and we prevent
more items from being queued up. For the source domain this means that we'll
stop accepting new commands as long as its pipe buffer is not empty.
Before we try to enqueue an item we first check whether it is possible to send
it further down the pipe, by attempting to recursively flush the pipes. This
ensures that we retain the order of events as much as possible.
We might break causality of watch events if the target domain's queue is full
and we need to start using the watch's queue. This is a breaking change in
the xenstore protocol, but only for domains which are not processing their
incoming ring as expected.
When a watch is deleted its entire pending queue is dropped (no code is needed
for that, because it is part of the 'watch' type).
There is a cache of watches that have pending events that we attempt to flush
at every cycle if possible.
Introduce 3 limits here:
* quota-maxwatchevents on watch event destination: when this is hit the
source will not be allowed to queue up more watch events.
* quota-maxoustanding which is the number of responses not read from the ring:
once exceeded, no more inputs are processed until all outstanding replies
are consumed by the client.
* overflow queue on the watch event source: all watches that cannot be stored
on destination are queued up here, a single command can trigger multiple
watches (e.g. due to recursion).
The overflow queue currently doesn't have an upper bound, it is difficult to
accurately calculate one as it depends on whether you are Dom0 and how many
watches each path has registered and how many watch events you can trigger
with a single command (e.g. a commit). However these events were already
using memory, this just moves them elsewhere, and as long as we correctly
block a domain it shouldn't result in unbounded memory usage.
Note that Dom0 is not excluded from these checks, it is important that Dom0 is
especially not excluded when it is the source, since there are many ways in
which a guest could trigger Dom0 to send it watch events.
This should protect against malicious frontends as long as the backend follows
the PV xenstore protocol and only exposes paths needed by the frontend, and
changes those paths at most once as a reaction to guest events, or protocol
state.
The queue limits are per watch, and per domain-pair, so even if one
communication channel would be "blocked", others would keep working, and the
domain itself won't get blocked as long as it doesn't overflow the queue of
watch events.
Similarly a malicious backend could cause the frontend to get blocked, but
this watch queue protects the frontend as well as long as it follows the PV
protocol. (Although note that protection against malicious backends is only a
best effort at the moment)
This is part of XSA-326 / CVE-2022-42318.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Ensures we cannot store more than [capacity] elements in a [Queue]. Replacing
all Queue with this module will then ensure at compile time that all Queues
are correctly bound checked.
Each element in the queue has a class with its own limits. This, in a
subsequent change, will ensure that command responses can proceed during a
flood of watch events.
No functional change.
This is part of XSA-326.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
The queue here would only ever hold at most one element. This will simplify
follow-up patches.
This is part of XSA-326.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Using a full path to the C libraries when preparing one of the ocaml
binding for those libraries make the binding unusable by external
project. The full path is somehow embedded and reused by the external
project when linking against the binding.
Instead, we will use the proper way to link a library, by using '-l'.
For in-tree build, we also need to provide the search directory via
'-L'.
(The search path -L are still be embedded, but at least that doesn't
prevent the ocaml binding from been used.)
Related-to: xen-project/xen#96
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>
The current bindings function, but the preexisting
type physinfo_arch_cap_flag =
| X86 of x86_physinfo_arch_cap_flag
is a special case in the Ocaml type system with an unusual indirection, and
will break when a second option, e.g. `| ARM of ...` is added.
Also, the position the list is logically wrong. Currently, the types express
a list of elements which might be an x86 flag or an arm flag (and can
intermix), whereas what we actually want is either a list of x86 flags, or a
list of ARM flags (that cannot intermix).
Rework the Ocaml types to avoid the ABI special case and move the list
primitive, and adjust the C bindings to match.
Fixes: 2ce11ce249 ("x86/HVM: allow per-domain usage of hardware virtualized APIC")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>
Reposition the defines to match the outer style and to make the logic
half-legible.
No functional change.
Fixes: 0570d7f276 ("x86/msr: introduce an option for compatible MSR behavior selection")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>
Hiding the type will make it easier to change the implementation
in the future without breaking code that relies on it.
No functional change.
Signed-off-by: Edwin Török <edvin.torok@citrix.com>
Acked-by: Christian Lindig <christian.lindig@citrix.com>
Andrew Cooper
Javi Merino
Andrii Sultanov
Petr Beneš
Roger Pau Monné
Edwin Török
Luca Fancellu
Alejandro Vallejo
Juergen Gross
Edwin Török
Anthony PERARD