To combat GPZ SP4 "Speculative Store Bypass", Intel have extended their
speculative sidechannel mitigations specification as follows:
* A feature bit to indicate that Speculative Store Bypass Disable is
supported.
* A new bit in MSR_SPEC_CTRL which, when set, disables memory disambiguation
in the pipeline.
* A new bit in MSR_ARCH_CAPABILITIES, which will be set in future hardware,
indicating that the hardware is not susceptible to Speculative Store Bypass
sidechannels.
For contemporary processors, this interface will be implemented via a
microcode update.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
AMD processors will execute loads and stores with the same base register in
program order, which is typically how a compiler emits code.
Therefore, by default no mitigating actions are taken, despite there being
corner cases which are vulnerable to the issue.
For performance testing, or for users with particularly sensitive workloads,
the `spec-ctrl=ssbd` command line option is available to force Xen to disable
Memory Disambiguation on applicable hardware.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
In hindsight, the options for `bti=` aren't as flexible or useful as expected
(including several options which don't appear to behave as intended).
Changing the behaviour of an existing option is problematic for compatibility,
so introduce a new `spec-ctrl=` in the hopes that we can do better.
One common way of deploying Xen is with a single PV dom0 and all domUs being
HVM domains. In such a setup, an administrator who has weighed up the risks
may wish to forgo protection against malicious PV domains, to reduce the
overall performance hit. To cater for this usecase, `spec-ctrl=no-pv` will
disable all speculative protection for PV domains, while leaving all
speculative protection for HVM domains intact.
For coding clarity as much as anything else, the suboptions are grouped by
logical area; those which affect the alternatives blocks, and those which
affect Xen's in-hypervisor settings. See the xen-command-line.markdown for
full details of the new options.
While changing the command line options, take the time to change how the data
is reported to the user. The three DEBUG printks are upgraded to unilateral,
as they are all relevant pieces of information, and the old "mitigations:"
line is split in the two logical areas described above.
Sample output from booting with `spec-ctrl=no-pv` looks like:
(XEN) Speculative mitigation facilities:
(XEN) Hardware features: IBRS/IBPB STIBP IBPB
(XEN) Compiled-in support: INDIRECT_THUNK
(XEN) Xen settings: BTI-Thunk RETPOLINE, SPEC_CTRL: IBRS-, Other: IBPB
(XEN) Support for VMs: PV: None, HVM: MSR_SPEC_CTRL RSB
(XEN) XPTI (64-bit PV only): Dom0 enabled, DomU enabled
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
credit2_cap_period_ms isn't mentioned in xen-command-line.markdown.
Add a description.
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Many of the architecture specific boot parameters are not qualified
as such. Correct that. Reorder PKU to be alphabetical.
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Avoid flushing the complete TLB when switching %cr3 for mitigation of
Meltdown by using the PCID feature if available.
We are using 4 PCID values for a 64 bit pv domain subject to XPTI and
2 values for the non-XPTI case:
- guest active and in kernel mode
- guest active and in user mode
- hypervisor active and guest in user mode (XPTI only)
- hypervisor active and guest in kernel mode (XPTI only)
We use PCID only if PCID _and_ INVPCID are supported. With PCID in use
we disable global pages in cr4. A command line parameter controls in
which cases PCID is being used.
As the non-XPTI case has shown not to perform better with PCID at least
on some machines the default is to use PCID only for domains subject to
XPTI.
With PCID enabled we always disable global pages. This avoids having to
either flush the complete TLB or do a cycle through all PCID values
when invalidating a single global page.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
If possible use the INVPCID instruction for flushing the TLB instead of
toggling cr4.pge for that purpose.
While at it remove the dependency on cr4.pge being required for mtrr
loading, as this will be required later anyway.
Add a command line option "invpcid" for controlling the use of
INVPCID (default to true).
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Instead of switching XPTI globally on or off add a per-domain flag for
that purpose. This allows to modify the xpti boot parameter to support
running dom0 without Meltdown mitigations. Using "xpti=no-dom0" as boot
parameter will achieve that.
Move the xpti boot parameter handling to xen/arch/x86/pv/domain.c as
it is pv-domain specific.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Some underscores are not escaped in xen-command-line.markdown.
Correct that.
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
Some of the boot parameters in docs/misc/xen-command-line.markdown are
not in the correct alphabetically order. Correct that.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
Xen does not properly support big.LITTLE platform. All vCPUs of a guest
will always have the MIDR of the boot CPU (see arch_domain_create).
At best the guest may see unreliable performance (vCPU switching between
big and LITTLE), at worst the guest will become unreliable or insecure.
This is becoming more apparent with branch predictor hardening in Linux
because they target a specific kind of CPUs and may not work on other
CPUs.
For the time being, park any CPUs with a MDIR different from the boot
CPU. This will be revisited in the future once Xen gains understanding
of big.LITTLE.
[1] https://lists.xenproject.org/archives/html/xen-devel/2016-12/msg00826.html
Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Oleksandr Tyshchenkko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Jan Beulich <jbeulich@suse.com>
This patch was originally released as part of XSA-226. It retains the same
command line syntax (as various downstreams are mitigating XSA-226 using this
mechanism) but the defaults have been updated due to the revised XSA-226
patched, after which transitive grants are believed to functioning
properly.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
The current XPTI implementation isolates the directmap (and therefore a lot of
guest data), but a large quantity of CPU0's state (including its stack)
remains visible.
Furthermore, an attacker able to read .text is in a vastly superior position
to normal when it comes to fingerprinting Xen for known vulnerabilities, or
scanning for ROP/Spectre gadgets.
Collect together the entrypoints in .text.entry (currently 3x4k frames, but
can almost certainly be slimmed down), and create a common mapping which is
inserted into each per-cpu shadow. The stubs are also inserted into this
mapping by pointing at the in-use L2. This allows stubs allocated later (SMP
boot, or CPU hotplug) to work without further changes to the common mappings.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Support both a "disable everything" and a "disable all RSB overwriting"
sub-option.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Issuing an IBPB command flushes the Branch Target Buffer, so that any poison
left by one vcpu won't remain when beginning to execute the next.
The cost of IBPB is substantial, and skipped on transition to idle, as Xen's
idle code is robust already. All transitions into vcpu context are fully
serialising in practice (and under consideration for being retroactively
declared architecturally serialising), so a cunning attacker cannot use SP1 to
try and skip the flush.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
See the logic and comments in init_speculation_mitigations() for further
details.
There are two controls for RSB overwriting, because in principle there are
cases where it might be safe to forego rsb_native (Off the top of my head,
SMEP active, no 32bit PV guests at all, no use of vmevent/paging subsystems
for HVM guests, but I make no guarantees that this list of restrictions is
exhaustive).
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
shim_mem will now account for both the memory used by the hypervisor
loaded in memory and the free memory slack given to the shim for
runtime usage.
From experimental testing it seems like the total amount of MiB used
by the shim (giving it ~1MB of free memory for runtime) is:
memory/113 + 20
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Instead of gaining yet another top level boolean, introduce a more generic
cpuid= option. Also introduce a helper function to parse a generic boolean
value.
This is part of XSA-254.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Depending on hardware and microcode availability, we will want to replace
IND_THUNK_REPOLINE with other implementations.
For AMD hardware, choose IND_THUNK_LFENCE in preference to retpoline if lfence
is known to be (or was successfully made) dispatch serialising.
This is part of XSA-254.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
First of all we don't need it on AMD systems. Additionally allow its use
to be controlled by command line option. For best backportability, this
intentionally doesn't use alternative instruction patching to achieve
the intended effect - while we likely want it, this will be later
follow-up.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Allowing pagetables to point to other pagetables of the same level
(often called 'linear pagetables') has been included in Xen since its
inception; but recently it has been the source of a number of subtle
reference-counting bugs.
It is not used by Linux or MiniOS; but it is used by NetBSD and Novell
Netware. There are significant numbers of people who are never going
to use the feature, along with significant numbers who need the
feature.
Add a Kconfig option for the feature (default to 'y'). Also add a
command-line option to control whether PV linear pagetables are
allowed (default to 'true').
NB that we leave linear_pt_count in the page struct. It's in a union,
so its presence doesn't increase the size of the data struct.
Changing the layout of the other elements based on configuration
options is asking for trouble however; so we'll just leave it there
and ASSERT that it's zero.
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>
Make it possible for the user to specify, with the boot
time parameter rcu-idle-timer-period-ms, how frequently
a CPU that went idle with pending RCU callbacks should be
woken up to check if the grace period ended.
Typical values (i.e., some of the values used by Linux as
the tick frequency) are 10, 4 or 1 ms. Default valus (used
when this parameter is not specified) is 10ms. Maximum is
100ms.
Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Instead of using the same global resource limits of grant tables (max.
number of grant frames, max. number of maptrack frames) for all domains
make these limits per domain. Set those per-domain limits in
grant_table_set_limits(). The global settings are serving as an upper
boundary now which must not be exceeded by a per-domain value. The
default of max_grant_frames is set to the maximum default xl will use.
While updating the semantics of the boot parameters remove the
documentation of the no longer existing gnttab_max_nr_frames and
correct the default gnttab_max_maptrack_frames uses.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com> [non-ARM parts]
Acked-by: Julien Grall <julien.grall@arm.com>
Support modifying conswitch, console_timestamps, loglvl and
guest_loglvl at runtime.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Delete the user visible option and code for PV superpage support. The
mm code is modified as if the option is set to false (the default
value).
Return the address space occupied by spage_info back to the reserved
address space.
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
The patch introduces a new command line option 'cpu' that when used will create
runqueue per logical pCPU. This may be useful for small systems, and also for
development, performance evalution and comparison.
Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
kexec: Provide user friendly option for memory limit
grub2 requires that the '<' character be escaped which is
inconvienet for users, provide a more natural specifier.
Signed-off-by: Simon Crowe <Simon.Crowe@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
iommu_inclusive_mapping is enabled by default (and has been for a long time).
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Also "correct" -> "incorrect" in the text.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
The ARM GICv3 provides a new kind of interrupt called LPIs.
The pending bits and the configuration data (priority, enable bits) for
those LPIs are stored in tables in normal memory, which software has to
provide to the hardware.
Allocate the required memory, initialize it and hand it over to each
redistributor. The maximum number of LPIs to be used can be adjusted with
the command line option "max_lpi_bits", which defaults to 20 bits,
covering about one million LPIs.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Julien Grall <julien.grall@arm.com>
In cases where one is absolutely sure that there will be
less vCPUs than pCPUs, having to pay the cost, mostly in
terms of overhead, of an advanced scheduler may be not
desirable.
The simple scheduler implemented here could be a solution.
Here how it works:
- each vCPU is statically assigned to a pCPU;
- if there are pCPUs without any vCPU assigned, they
stay idle (as in, the run their idle vCPU);
- if there are vCPUs which are not assigned to any
pCPU (e.g., because there are more vCPUs than pCPUs)
they *don't* run, until they get assigned;
- if a vCPU assigned to a pCPU goes away, one of the
waiting to be assigned vCPU, if any, gets assigned
to the pCPU and can run there.
This scheduler, therefore, if used in configurations
where every vCPUs can be assigned to a pCPU, guarantees
low overhead, low latency, and consistent performance.
If used as default scheduler, at Xen boot, it is
recommended to limit the number of Dom0 vCPUs (e.g., with
'dom0_max_vcpus=x'). Otherwise, all the pCPUs will have
one Dom0's vCPU assigned, and there won't be room for
running efficiently (if at all) any guest.
Target use cases are embedded and HPC, but it may well
be interesting also in circumnstances.
Kconfig and documentation are update accordingly.
While there, also document the availability of sched=rtds
as boot parameter, which apparently had been forgotten.
Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
In order to distinguish guest-generated SErrors from hypervisor-generated
SErrors we have to place SError checking code in every EL1 <-> EL2 paths.
That will cause overhead on entries and exits due to dsb/isb.
However, not all platforms want to categorize SErrors. For example, a host
that is running with trusted guests. The administrator can confirm that
all guests that are running on the host will not trigger such SErrors. In
this use-case, we should provide some options to administrators to avoid
categorizing SErrors and then reduce the overhead of dsb/isb.
We provided the following 3 options to administrators to determine how
the hypervisors handle SErrors:
* `diverse`:
The hypervisor will distinguish guest SErrors from hypervisor SErrors.
The guest generated SErrors will be forwarded to guests, the hypervisor
generated SErrors will cause the whole system to crash.
It requires:
1. dsb/isb on all EL1 -> EL2 trap entries to categorize SErrors
correctly.
2. dsb/isb on EL2 -> EL1 return paths to prevent slipping hypervisor
SErrors to guests.
3. dsb/isb in context switch to isolate SErrors between 2 vCPUs.
* `forward`:
The hypervisor will not distinguish guest SErrors from hypervisor
SErrors. All SErrors will be forwarded to guests, except the SErrors
generated when the idle vCPU is running. The idle domain doesn't have
the ability to handle SErrors, so we have to crash the whole system when
we get SErros with the idle vCPU. This option will avoid most overhead
of the dsb/isb, except the dsb/isb in context switch which is used to
isolate the SErrors between 2 vCPUs.
* `panic`:
The hypervisor will not distinguish guest SErrors from hypervisor SErrors.
All SErrors will crash the whole system. This option will avoid all
overhead of the dsb/isb pairs.
Signed-off-by: Wei Chen <Wei.Chen@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Having an off by default option allowing guests to join
_any_ shared pool is not very secure.
Lets eliminate tmem_shared_auth bootup option (which
was disabled by default) and have the code force this by default.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Classic PV shadow paging Dom0 has been broken for years, and can't
possibly be configured after 4045953.
PVH shadow paging Dom0 should still be possible.
Change the code and documentation to clarify that.
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper@citrix.com>
The current threshold before the guest issues the hypercall is, and always
has been, hard-coded to 2047. It is not clear where this number came
from so, to at least allow for ease of experimentation, this patch makes
the threshold tunable via the Xen command line.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
The Hypervisor Top Level Functional Specification v5.0a states in section
2.5:
"The hypervisor version information is encoded in leaf 0x40000002. Two
version numbers are provided: the main version and the service version.
The main version includes a major and minor version number and a build
number. These correspond to Microsoft Windows release numbers."
It also goes on to advise clients (i.e. guest versions of Windows) to use
the following algorithm to determine compatibility with the hypervisor
enlightenments:
if <your-main-version> greater than <hypervisor-main-version>
{
your version is compatible
}
else if <your-main-version> equal to <hypervisor-main-version> and
<your-service-version> greater than or equal to <hypervisor-service-version>
{
your version is compatible
}
else
{
your version is NOT compatible
}
So, clearly putting Xen hypervisor version information in that leaf is
spurious, but we probably get away with it because Xen's major version
is lower than the major version of Windows in which Hyper-V first
appeared (Server 2008).
This patch changes the leaf to use the kernel major and minor
versions, and build number from Windows Server 2008 (64-bit) by default.
These default values can be overriden from the Xen command line using new
'viridian-version' parameter.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Introduce new Xen command line parameter called "vwfi", which stands for
virtual wfi. The default is "trap": Xen traps guest wfi and wfe
instructions. In the case of wfi, Xen calls vcpu_block on the guest
vcpu; in the case of guest wfe, Xen calls vcpu_yield on the guest vcpu.
The behavior can be changed by setting vwfi to "native", in that case
Xen doesn't trap neither wfi nor wfe, running them in guest context.
The result is strong reduction in irq latency (from 5000ns to 2000ns,
measured using https://github.com/edgarigl/tbm, the physical timer, and
1 pcpu dedicated to 1 vcpu). The downside is that the scheduler thinks
that the guest is busy when actually is sleeping, leading to suboptimal
scheduling decisions.
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>
As some users have suggested, elaborate the usage of RMRR specification
on the command line, and provide a usage example.
Also, always treat the specified page numbers as hexadecimal values.
Signed-off-by: Venu Busireddy <venu.busireddy@oracle.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
The default dom0_mem is 128M which is not sufficient to boot a Ubuntu
based Dom0. It is not clear what a better default value could be.
Instead, loudly warn the user when dom0_mem is unspecified and wait 3
secs. Then use 512M.
Update the docs to specify that dom0_mem is required on ARM. (The
current xen-command-line document does not actually reflect the current
behavior of dom0_mem on ARM correctly.)
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Split the Dom0 builder into two different functions, one for PV (and classic
PVH), and another one for PVHv2. Introduce a new command line parameter called
'dom0' that can be used to request the creation of a PVHv2 Dom0 by setting the
'hvm' sub-option. A panic has also been added if a user tries to use dom0=hvm
until all the code is in place, then the panic will be removed.
While there mark the dom0_shadow option that was used by PV Dom0 as deprecated,
it was lacking documentation and was not functional. Point users towards
dom0=shadow instead.
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Andrew Cooper
Juergen Gross
Wei Liu
Stefano Stabellini
Julien Grall
Jan Beulich
Roger Pau Monne
Sergey Dyasli
George Dunlap
Dario Faggioli
Praveen Kumar
Simon Crowe
Swapnil Paratey
Andre Przywara
Wei Chen
Konrad Rzeszutek Wilk
Paul Durrant
Venu Busireddy