Commit Graph
35654 Commits
Author SHA1 Message Date
Andrew Cooper 68c76d71e0 x86/boot: Calculate the most appropriate BTI mitigation to use
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>

x86/spec_ctrl: Fix determination of when to use IBRS

The original version of this logic was:

    /*
     * On Intel hardware, we'd like to use retpoline in preference to
     * IBRS, but only if it is safe on this hardware.
     */
    else if ( boot_cpu_has(X86_FEATURE_IBRSB) )
    {
        if ( retpoline_safe() )
            thunk = THUNK_RETPOLINE;
        else
            ibrs = true;
    }

but it was changed by a request during review.  Sadly, the result is buggy as
it breaks the later fallback logic by allowing IBRS to appear as available
when in fact it isn't.

This in practice means that on repoline-unsafe hardware without IBRS, we
select THUNK_JUMP despite intending to select THUNK_RETPOLINE.

Reported-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 2713715305
master date: 2018-01-26 14:10:21 +0000
master commit: 30cbd0c83e
master date: 2018-02-06 18:32:58 +0000
2018-02-08 12:30:46 +01:00
Andrew Cooper bda328363f x86/entry: Avoid using alternatives in NMI/#MC paths
This patch is deliberately arranged to be easy to revert if/when alternatives
patching becomes NMI/#MC safe.

For safety, there must be a dispatch serialising instruction in (what is
logically) DO_SPEC_CTRL_ENTRY so that, in the case that Xen needs IBRS set in
context, an attacker can't speculate around the WRMSR and reach an indirect
branch within the speculation window.

Using conditionals opens this attack vector up, so the else clause gets an
LFENCE to force the pipeline to catch up before continuing.  This also covers
the safety of RSB conditional, as execution it is guaranteed to either hit the
WRMSR or LFENCE.

One downside of not using alternatives is that there unconditionally an LFENCE
in the IST path in cases where we are not using the features from IBRS-capable
microcode.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 3fffaf9c13
master date: 2018-01-26 14:10:21 +0000
2018-02-08 12:30:06 +01:00
Andrew Cooper a24b7553f9 x86/entry: Organise the clobbering of the RSB/RAS on entry to Xen
ret instructions are speculated directly to values recorded in the Return
Stack Buffer/Return Address Stack, as there is no uncertainty in well-formed
code.  Guests can take advantage of this in two ways:

  1) If they can find a path in Xen which executes more ret instructions than
     call instructions.  (At least one in the waitqueue infrastructure,
     probably others.)

  2) Use the fact that the RSB/RAS in hardware is actually a circular stack
     without a concept of empty.  (When it logically empties, stale values
     will start being used.)

To mitigate, overwrite the RSB on entry to Xen with gadgets which will capture
and contain rogue speculation.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: e6c0128e9a
master date: 2018-01-26 14:10:21 +0000
2018-02-08 12:29:28 +01:00
Andrew Cooper 13a30ba54c x86/entry: Organise the use of MSR_SPEC_CTRL at each entry/exit point
We need to be able to either set or clear IBRS in Xen context, as well as
restore appropriate guest values in guest context.  See the documentation in
asm-x86/spec_ctrl_asm.h for details.

With the contemporary microcode, writes to %cr3 are slower when SPEC_CTRL.IBRS
is set.  Therefore, the positioning of SPEC_CTRL_{ENTRY/EXIT}* is important.

Ideally, the IBRS_SET/IBRS_CLEAR hunks might be positioned either side of the
%cr3 change, but that is rather more complicated to arrange, and could still
result in a guest controlled value in SPEC_CTRL during the %cr3 change,
negating the saving if the guest chose to have IBRS set.

Therefore, we optimise for the pre-Skylake case (being far more common in the
field than Skylake and later, at the moment), where we have a Xen-preferred
value of IBRS clear when switching %cr3.

There is a semi-unrelated bugfix, where various asm_defn.h macros have a
hidden dependency on PAGE_SIZE, which results in an assembler error if used in
a .macro definition.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 5e79629011
master date: 2018-01-26 14:10:21 +0000
2018-02-08 12:28:35 +01:00
Andrew Cooper 0177bf5d25 x86/hvm: Permit guests direct access to MSR_{SPEC_CTRL,PRED_CMD}
For performance reasons, HVM guests should have direct access to these MSRs
when possible.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
master commit: 5a2fe17114
master date: 2018-01-26 14:10:21 +0000
2018-02-08 12:27:50 +01:00
Andrew Cooper 2fdee60ec1 x86/migrate: Move MSR_SPEC_CTRL on migrate
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 0cf2a4eb76
master date: 2018-01-26 14:10:21 +0000
2018-02-08 12:27:18 +01:00
Andrew Cooper 186c3c6e94 x86: Avoid corruption on migrate for vcpus using CPUID Faulting
Xen 4.8 and later virtualises CPUID Faulting support for guests.  However, the
value of MSR_MISC_FEATURES_ENABLES is omitted from the vcpu state, meaning
that the current cpuid faulting setting is lost on migrate/suspend/resume.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: b90f86be16
master date: 2017-12-01 18:09:48 +0000
2018-02-08 12:26:54 +01:00
Andrew Cooper e57d4d043b x86/msr: Emulation of MSR_{SPEC_CTRL,PRED_CMD} for guests
As per the spec currently available here:

https://software.intel.com/sites/default/files/managed/c5/63/336996-Speculative-Execution-Side-Channel-Mitigations.pdf

MSR_ARCH_CAPABILITIES will only come into existence on new hardware, but is
implemented as a straight #GP for now to avoid being leaky when new hardware
arrives.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: ea58a679a6
master date: 2018-01-26 14:10:21 +0000
2018-02-08 12:21:59 +01:00
Andrew Cooper 1dcfd39519 x86/cpuid: Handling of IBRS/IBPB, STIBP and IBRS for guests
Intel specifies IBRS/IBPB (combined, in a single bit) and STIBP as a separate
bit.  AMD specifies IBPB alone in a 3rd bit.

AMD's IBPB is a subset of Intel's combined IBRS/IBPB.  For performance
reasons, administrators might wish to express "IBPB only" even on Intel
hardware, so we allow the AMD bit to be used for this purpose.

The behaviour of STIBP is more complicated.

It is our current understanding that STIBP will be advertised on HT-capable
hardware irrespective of whether HT is enabled, but not advertised on
HT-incapable hardware.  However, for ease of virtualisation, STIBP's
functionality is ignored rather than reserved by microcode/hardware on
HT-incapable hardware.

For guest safety, we treat STIBP as special, always override the toolstack
choice, and always advertise STIBP if IBRS is available.  This removes the
corner case where STIBP is not advertised, but the guest is running on
HT-capable hardware where it does matter.

Finally as a bugfix, update the libxc CPUID logic to understand the e8b
feature leaf, which has the side effect of also offering CLZERO to guests on
applicable hardware.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: d297b56682
master date: 2018-01-26 14:10:21 +0000
2018-02-08 12:21:25 +01:00
Wei Liu f11cf29f27 x86: fix GET_STACK_END
AIUI the purpose of having the .if directive is to make GET_STACK_END
work with any general purpose registers. The code as-is would produce
the wrong result for r8. Fix it.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 8155476765
master date: 2018-01-25 11:34:17 +0000
2018-02-08 12:20:45 +01:00
Roger Pau Monné bd53bc8506 x86/acpi: process softirqs while printing CPU ACPI data
Or else the watchdog triggers on boxes with a huge number of CPUs

Reported-by: Simon Crowe <simon.crowe@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: a5579ee79e
master date: 2018-01-24 18:02:14 +0100
2018-02-08 12:20:19 +01:00
Andrew Cooper 764804938c x86/cmdline: Introduce a command line option to disable IBRS/IBPB, STIBP and IBPB
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>

xen/cmdline: Fix parse_boolean() for unadorned values

A command line such as "cpuid=no-ibrsb,no-stibp" tickles a bug in
parse_boolean() because the separating comma fails the NUL case.

Instead, check for slen == nlen which accounts for the boundary (if any)
passed via the 'e' parameter.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 7850b1c007
master date: 2018-01-16 17:45:50 +0000
master commit: ac37ec1dde
master date: 2018-01-31 10:47:12 +0000
2018-02-08 12:19:40 +01:00
Andrew Cooper 602633eb73 x86/feature: Definitions for Indirect Branch Controls
Contemporary processors are gaining Indirect Branch Controls via microcode
updates.  Intel are introducing one bit to indicate IBRS and IBPB support, and
a second bit for STIBP.  AMD are introducing IBPB only, so enumerate it with a
separate bit.

Furthermore, depending on compiler and microcode availability, we may want to
run Xen with IBRS set, or clear.

To use these facilities, we synthesise separate IBRS and IBPB bits for
internal use.  A lot of infrastructure is required before these features are
safe to offer to guests.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
master commit: 0d703a701c
master date: 2018-01-16 17:45:50 +0000
2018-02-08 12:18:57 +01:00
Andrew Cooper 6fef46d6fb x86: Introduce alternative indirect thunks
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>
master commit: 858cba0d4c
master date: 2018-01-16 17:45:50 +0000
2018-02-08 12:18:22 +01:00
Andrew Cooper 30b99299d6 x86/amd: Try to set lfence as being Dispatch Serialising
This property is required for the AMD's recommended mitigation for Branch
Target Injection, but Xen needs to cope with being unable to detect or modify
the MSR.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: fe3ee5530a
master date: 2018-01-16 17:45:50 +0000
2018-02-08 12:17:42 +01:00
Andrew Cooper 447dce891f x86/boot: Report details of speculative mitigations
Nothing very interesting at the moment, but the logic will grow as new
mitigations are added.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: 31d6c53adf
master date: 2018-01-16 17:45:50 +0000
2018-02-08 12:16:50 +01:00
Andrew Cooper 29df8a5c4d x86: Support indirect thunks from assembly code
Introduce INDIRECT_CALL and INDIRECT_JMP which either degrade to a normal
indirect branch, or dispatch to the __x86_indirect_thunk_* symbols.

Update all the manual indirect branches in to use the new thunks.  The
indirect branches in the early boot and kexec path are left intact as we can't
use the compiled-in thunks at those points.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 7c508612f7
master date: 2018-01-16 17:45:50 +0000
2018-02-08 12:15:37 +01:00
Andrew Cooper 6403b5048d x86: Support compiling with indirect branch thunks
Use -mindirect-branch=thunk-extern/-mindirect-branch-register when available.
To begin with, use the retpoline thunk.  Later work will add alternative
thunks which can be selected at boot time.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: 3659f0f4bc
master date: 2018-01-16 17:45:50 +0000
2018-02-08 12:14:35 +01:00
Andrew Cooper 628b6af24f common/wait: Clarifications to wait infrastructure
This logic is not as clear as it could be.  Add some comments to help.

Rearrange the asm block in __prepare_to_wait() to separate the GPR
saving/restoring from the internal logic.

While tweaking, add an unreachable() following the jmp in
check_wakeup_from_wait().

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 2d1c82261d
master date: 2018-01-05 19:57:08 +0000
2018-02-08 12:13:48 +01:00
Andrew Cooper 237a58b1d0 x86/entry: Erase guest GPR state on entry to Xen
This reduces the number of code gadgets which can be attacked with arbitrary
guest-controlled GPR values.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
master commit: 03bd8c3a70
master date: 2018-01-05 19:57:08 +0000
2018-02-08 12:13:15 +01:00
Andrew Cooper f0f7ce5e82 x86/hvm: Use SAVE_ALL to construct the cpu_user_regs frame after VMExit
No practical change.

One side effect in debug builds is that %rbp is inverted in the manner
expected by the stack unwinder to indicate a interrupt frame.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
master commit: 13682ca8c9
master date: 2018-01-05 19:57:08 +0000
2018-02-08 12:12:44 +01:00
Andrew Cooper d6e972508e x86/entry: Rearrange RESTORE_ALL to restore register in stack order
Results in a more predictable (i.e. linear) memory access pattern.

No functional change.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
master commit: f85d105e27
master date: 2018-01-05 19:57:08 +0000
2018-02-08 12:12:08 +01:00
Andrew Cooper 9aaa208886 x86: Introduce a common cpuid_policy_updated()
No practical change at the moment, but future changes will need to react
irrespective of guest type.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: b357546b43
master date: 2018-01-05 19:57:07 +0000
2018-02-08 12:11:22 +01:00
Andrew Cooper 40f9ae9d05 x86/hvm: Rename update_guest_vendor() callback to cpuid_policy_changed()
It will shortly be used for more than just changing the vendor.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 3bea00966e
master date: 2018-01-05 19:57:07 +0000
2018-02-08 12:10:40 +01:00
Andrew Cooper ade9554f87 x86/alt: Introduce ALTERNATIVE{,_2} macros
To help creating alternative frames in assembly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 4711428f5e
master date: 2018-01-05 19:57:07 +0000
2018-02-08 12:09:55 +01:00
Andrew Cooper a0ed0349ff x86/alt: Break out alternative-asm into a separate header file
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: 9d7b4351d3
master date: 2018-01-05 19:57:07 +0000
2018-02-08 12:08:50 +01:00
Julien Grall 4d01dbc713 xen/arm32: entry: Document the purpose of r11 in the traps handler
It took me a bit of time to understand why __DEFINE_TRAP_ENTRY is
storing the original stack pointer in r11. It is working in pair with
return_traps_entry where sp will be restored from r11.

This is fine because per the AAPCS r11 must be preserved by the
subroutine. So in return_from_trap, r11 will still contain the original
stack pointer.

Add some documentation in the code to point the 2 sides to each other.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit dd855aa430)
2018-02-07 08:39:30 -08:00
Julien Grall 22379b6adc xen/arm32: Invalidate icache on guest exist for Cortex-A15
In order to avoid aliasing attacks against the branch predictor on
Cortex A-15, let's invalidate the BTB on guest exit, which can only be
done by invalidating the icache (with ACTLR[0] being set).

We use the same hack as for A12/A17 to perform the vector decoding.

This is based on Linux patch from the kpti branch in [1].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 665c4b6aa7)
2018-02-07 08:39:25 -08:00
Julien Grall 6e13ad777d xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12
In order to avoid aliasing attackes agains the branch predictor, let's
invalidate the BTB on guest exist. This is made complicated by the fact
that we cannot take a branch invalidating the BTB.

This is based on the fourth version posted by Marc Zyngier on Linux-arm
mailing list (see [1]).

This is part of XSA-254.

[1] https://www.spinics.net/lists/arm-kernel/msg632062.html

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 05e0690d03)
2018-02-07 08:39:20 -08:00
Julien Grall 0d32237d5f xen/arm32: Add skeleton to harden branch predictor aliasing attacks
Aliasing attacked against CPU branch predictors can allow an attacker to
redirect speculative control flow on some CPUs and potentially divulge
information from one context to another.

This patch adds initiatial skeleton code behind a new Kconfig option
to enable implementation-specific mitigations against these attacks
for CPUs that are affected.

Most of mitigations will have to be applied when entering to the
hypervisor from the guest context.

Because the attack is against branch predictor, it is not possible to
safely use branch instruction before the mitigation is applied.
Therefore this has to be done in the vector entry before jump to the
helper handling a given exception.

However, on arm32, each vector contain a single instruction. This means
that the hardened vector tables may rely on the state of registers that
does not hold when in the hypervisor (e.g SP is 8 bytes aligned).
Therefore hypervisor code running with guest vectors table should be
minimized and always have IRQs and SErrors masked to reduce the risk to
use them.

This patch provides an infrastructure to switch vector tables before
entering to the guest and when leaving it.

Note that alternative could have been used, but older Xen (4.8 or
earlier) doesn't have support. So avoid using alternative to ease
backporting.

This is part of XSA-254.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 9bd4463b5c)
2018-02-07 08:39:14 -08:00
Julien Grall 4ba59bdc26 xen/arm32: entry: Add missing trap_reset entry
At the moment, the reset vector is defined as .word 0 (e.g andeq r0, r0,
r0).

This is rather unintuitive and will result to execute the trap
undefined. Instead introduce trap helpers for reset and will generate an
error message in the unlikely case that reset will be called.

This is part of XSA-254.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 00268cc912)

Conflicts:
	xen/arch/arm/arm32/traps.c
2018-02-07 08:38:57 -08:00
Julien Grall 2997c5e628 xen/arm32: Add missing MIDR values for Cortex-A17 and A12
Cortex-A17 and A12 MIDR will be used in a follow-up patch for hardening
the branch predictor.

This is part of XSA-254.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 340367bca5)
2018-02-07 08:37:40 -08:00
Julien Grall 751c8791d0 xen/arm32: entry: Consolidate DEFINE_TRAP_ENTRY_* macros
The only difference between all the DEFINE_TRAP_ENTRY_* macros  are the
interrupts (Asynchronous Abort, IRQ, FIQ) unmasked.

Rather than duplicating the code, introduce __DEFINE_TRAP_ENTRY macro
that will take the list of interrupts to unmask.

This is part of XSA-254.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 3bd8fd751e)
2018-02-07 08:37:35 -08:00
Julien Grall a2567d6b54 xen/arm: cpuerrata: Remove percpu.h include
The include percpu.h was added by mistake in cpuerrata.h (see commit
4c4fddc166 "xen/arm64: Add skeleton to harden the branch aliasing
attacks"). So remove it.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit a5e7ce9560)
2018-01-24 13:23:07 -08:00
Julien Grall 9f79e8d846 xen/arm64: Implement branch predictor hardening for affected Cortex-A CPUs
Cortex-A57, A72, A73 and A75 are susceptible to branch predictor
aliasing and can theoritically be attacked by malicious code.

This patch implements a PSCI-based mitigation for these CPUs when
available. The call into firmware will invalidate the branch predictor
state, preventing any malicious entries from affection other victim
contexts.

Ported from Linux git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
branch kpti.

 Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
 Signed-off-by: Will Deacon <will.deacon@arm.com>

This is part of XSA-254.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit e730f8e41e)
2018-01-24 13:23:07 -08:00
Julien Grall fba48eff18 xen/arm64: Add skeleton to harden the branch predictor aliasing attacks
Aliasing attacked against CPU branch predictors can allow an attacker to
redirect speculative control flow on some CPUs and potentially divulge
information from one context to another.

This patch adds initial skeleton code behind a new Kconfig option to
enable implementation-specific mitigations against these attacks for
CPUs that are affected.

Most of the mitigations will have to be applied when entering to the
hypervisor from the guest context. For safety, it is applied at every
exception entry. So there are potential for optimizing when receiving
an exception at the same level.

Because the attack is against branch predictor, it is not possible to
safely use branch instruction before the mitigation is applied.
Therefore, this has to be done in the vector entry before jump to the
helper handling a given exception.

On Arm64, each vector can hold 32 instructions. This leave us 31
instructions for the mitigation. The last one is the branch instruction
to the helper.

Because a platform may have CPUs with different micro-architectures,
per-CPU vector table needs to be provided. Realistically, only a few
different mitigations will be necessary. So provide a small set of
vector tables. They will be re-used and patch with the mitigations
on-demand.

This is based on the work done in Linux (see [1]).

This is part of XSA-254.

[1] git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
branch ktpi

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 4c4fddc166)
2018-01-24 13:22:58 -08:00
Julien Grall 3790833ef1 xen/arm: cpuerrata: Add MIDR_ALL_VERSIONS
Introduce a new macro MIDR_ALL_VERSIONS to match all variant/revision of a
given CPU model.

This is part of XSA-254.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit ba73070af4)

Conflicts:
	xen/arch/arm/cpuerrata.c
2018-01-24 13:17:15 -08:00
Julien Grall 50450c1f33 xen/arm64: Add missing MIDR values for Cortex-A72, A73 and A75
Cortex-A72, A73 and A75 MIDR will be used to a follow-up for hardening
the branch predictor.

This is part of XSA-254.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 7975bff524)
2018-01-24 13:16:35 -08:00
Julien Grall 2ec7ccbffc xen/arm: Introduce enable callback to enable a capabilities on each online CPU
Once Xen knows what features/workarounds present on the platform, it
might be necessary to configure each online CPU.

Introduce a new callback "enable" that will be called on each online CPU to
configure the "capability".

The code is based on Linux v4.14 (where cpufeature.c comes from), the
explanation of why using stop_machine_run is kept as we have similar
problem in the future.

Lastly introduce enable_errata_workaround that will be called once CPUs
have booted and before the hardware domain is created.

This is part of XSA-254.

Signed-of-by: Julien Grall <julien.grall@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit 7500495155)

Conflicts:
	xen/include/asm-arm/cpufeature.h
2018-01-24 13:16:19 -08:00
Jan Beulich dc7d46580d x86: allow Meltdown band-aid to be disabled
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>
master commit: e871e80c38
master date: 2018-01-16 17:50:59 +0100
2018-01-17 17:08:25 +01:00
Jan Beulich 1e0974638d x86: Meltdown band-aid against malicious 64-bit PV guests
This is a very simplistic change limiting the amount of memory a running
64-bit PV guest has mapped (and hence available for attacking): Only the
mappings of stack, IDT, and TSS are being cloned from the direct map
into per-CPU page tables. Guest controlled parts of the page tables are
being copied into those per-CPU page tables upon entry into the guest.
Cross-vCPU synchronization of top level page table entry changes is
being effected by forcing other active vCPU-s of the guest into the
hypervisor.

The change to context_switch() isn't strictly necessary, but there's no
reason to keep switching page tables once a PV guest is being scheduled
out.

This isn't providing full isolation yet, but it should be covering all
pieces of information exposure of which would otherwise require an XSA.

There is certainly much room for improvement, especially of performance,
here - first and foremost suppressing all the negative effects on AMD
systems. But in the interest of backportability (including to really old
hypervisors, which may not even have alternative patching) any such is
being left out here.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 5784de3e20
master date: 2018-01-16 17:49:03 +0100
2018-01-17 17:07:33 +01:00
Andrew Cooper 87ea781624 x86/mm: Always set _PAGE_ACCESSED on L4e updates
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: bd61fe94be
master date: 2018-01-15 13:53:16 +0000
2018-01-17 17:04:59 +01:00
Jan H. Schönherr 96990e27b0 x86: Don't use potentially incorrect CPUID values for topology information
Intel says for CPUID leaf 0Bh:

  "Software must not use EBX[15:0] to enumerate processor
   topology of the system. This value in this field
   (EBX[15:0]) is only intended for display/diagnostic
   purposes. The actual number of logical processors
   available to BIOS/OS/Applications may be different from
   the value of EBX[15:0], depending on software and platform
   hardware configurations."

And yet, we're using them to derive the number cores in a package
and the number of siblings in a core.

Derive the number of siblings and cores from EAX instead, which is
intended for that.

Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: d51baf310e
master date: 2018-01-08 10:48:24 +0000
2018-01-17 17:04:30 +01:00
Andrew Cooper 2213ffe1a2 x86/entry: Remove support for partial cpu_user_regs frames
Save all GPRs on entry to Xen.

The entry_int82() path is via a DPL1 gate, only usable by 32bit PV guests, so
can get away with only saving the 32bit registers.  All other entrypoints can
be reached from 32 or 64bit contexts.

This is part of XSA-254.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
master commit: f9eb74789a
master date: 2018-01-05 19:57:07 +0000
2018-01-17 17:03:51 +01:00
Roger Pau Monné c3774d13ee x86/upcall: inject a spurious event after setting upcall vector
In case the vCPU has pending events to inject. This fixes a bug that
happened if the guest mapped the vcpu info area using
VCPUOP_register_vcpu_info without having setup the event channel
upcall, and then setup the upcall vector.

In this scenario the guest would not receive any upcalls, because the
call to VCPUOP_register_vcpu_info would have marked the vCPU as having
pending events, but the vector could not be injected because it was
not yet setup.

This has not caused issues so far because all the consumers first
setup the vector callback and then map the vcpu info page, but there's
no limitation that prevents doing it in the inverse order.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 7b5b8ca7df
master date: 2018-01-04 14:29:16 +0100
2018-01-17 17:03:17 +01:00
Jan Beulich f559d506f3 x86/E820: don't overrun array
The bounds check needs to be done after the increment, not before, or
else it needs to use a one lower immediate. Also use word operations
rather than byte ones for both the increment and the compare (allowing
E820_BIOS_MAX to be more easily bumped, should the need ever arise).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 0036c9dbcd
master date: 2018-01-03 11:03:56 +0100
2018-01-17 17:02:43 +01:00
Jan Beulich f877aab480 x86/IRQ: conditionally preserve access permission on map error paths
Permissions that had been granted before should not be revoked when
handling unrelated errors.

Reported-by: HW42 <hw42@ipsumj.de>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 3443e68a77
master date: 2018-01-03 11:03:10 +0100
2018-01-17 17:01:26 +01:00
Oleksandr Tyshchenko 0c3d524100 xen/arm: vgic: Check for vgic handler to be initialized before dereferencing it
Since domain_vgic_free() can be called when the vgic_ops haven't been
initialised yet, always check that d->arch.vgic.handler is not a null.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit b1f1e492cd)
2018-01-11 12:22:32 -08:00
Oleksandr Tyshchenko 4d190d79b4 xen/arm: p2m: Check for p2m->domain to be initialized before releasing resources
Since p2m_teardown() can be called when p2m_init() haven't executed yet
we might deal with unitialized list "p2m->pages" which leads to crash.
To avoid this use back pointer to domain as end-of-initialization indicator.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
(cherry picked from commit abd91b2a2b)
2018-01-11 12:22:14 -08:00
Stefano Stabellini a4a4abf8e8 arm: configure interrupts to be in non-secure group1
Xen uses non-secure group1 interrupts, however it doesn't configure the
GICv3 accordingly. Xen needs to set GICD_IGROUPR for SPIs and
GICR_IGROUPR0 for local interrupt to "1" to specify that interrupts
belong to group1. This is particularly important if the system has
GICD_CTLR.DS set, also see commit
7c9b973061b03af62734f613f6abec46c0dd4a88 in Linux.

Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Julien Grall <julien.grall@linaro.org>
Released-acked-by: Julien Grall <julien.grall@linaro.org>
(cherry picked from commit 0c8055c2f4)
2018-01-11 12:21:37 -08:00