Merge tag 'perf-core-for-mingo-5.4-20190814' of...

The following CVE entries describe Spectre variants:

   =============   =======================  =================

   =============   =======================  ==========================

   CVE-2017-5753   Bounds check bypass      Spectre variant 1

   CVE-2017-5715   Branch target injection  Spectre variant 2

   =============   =======================  =================

   CVE-2019-1125   Spectre v1 swapgs        Spectre variant 1 (swapgs)

   =============   =======================  ==========================

Problem

-------

over the network, see :ref:`[12] <spec_ref12>`. However such attacks

are difficult, low bandwidth, fragile, and are considered low risk.

Note that, despite "Bounds Check Bypass" name, Spectre variant 1 is not

only about user-controlled array bounds checks.  It can affect any

conditional checks.  The kernel entry code interrupt, exception, and NMI

handlers all have conditional swapgs checks.  Those may be problematic

in the context of Spectre v1, as kernel code can speculatively run with

a user GS.

Spectre variant 2 (Branch Target Injection)

-------------------------------------------

1. A user process attacking the kernel

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Spectre variant 1

~~~~~~~~~~~~~~~~~

   The attacker passes a parameter to the kernel via a register or

   via a known address in memory during a syscall. Such parameter may

   be used later by the kernel as an index to an array or to derive

   potentially be influenced for Spectre attacks, new "nospec" accessor

   macros are used to prevent speculative loading of data.

   Spectre variant 2 attacker can :ref:`poison <poison_btb>` the branch

Spectre variant 1 (swapgs)

~~~~~~~~~~~~~~~~~~~~~~~~~~

   An attacker can train the branch predictor to speculatively skip the

   swapgs path for an interrupt or exception.  If they initialize

   the GS register to a user-space value, if the swapgs is speculatively

   skipped, subsequent GS-related percpu accesses in the speculation

   window will be done with the attacker-controlled GS value.  This

   could cause privileged memory to be accessed and leaked.

   For example:

   ::

     if (coming from user space)

         swapgs

     mov %gs:<percpu_offset>, %reg

     mov (%reg), %reg1

   When coming from user space, the CPU can speculatively skip the

   swapgs, and then do a speculative percpu load using the user GS

   value.  So the user can speculatively force a read of any kernel

   value.  If a gadget exists which uses the percpu value as an address

   in another load/store, then the contents of the kernel value may

   become visible via an L1 side channel attack.

   A similar attack exists when coming from kernel space.  The CPU can

   speculatively do the swapgs, causing the user GS to get used for the

   rest of the speculative window.

Spectre variant 2

~~~~~~~~~~~~~~~~~

   A spectre variant 2 attacker can :ref:`poison <poison_btb>` the branch

   target buffer (BTB) before issuing syscall to launch an attack.

   After entering the kernel, the kernel could use the poisoned branch

   target buffer on indirect jump and jump to gadget code in speculative

The possible values in this file are:

  =======================================  =================================

  'Mitigation: __user pointer sanitation'  Protection in kernel on a case by

                                           case base with explicit pointer

                                           sanitation.

  =======================================  =================================

  .. list-table::

     * - 'Not affected'

       - The processor is not vulnerable.

     * - 'Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers'

       - The swapgs protections are disabled; otherwise it has

         protection in the kernel on a case by case base with explicit

         pointer sanitation and usercopy LFENCE barriers.

     * - 'Mitigation: usercopy/swapgs barriers and __user pointer sanitization'

       - Protection in the kernel on a case by case base with explicit

         pointer sanitation, usercopy LFENCE barriers, and swapgs LFENCE

         barriers.

However, the protections are put in place on a case by case basis,

and there is no guarantee that all possible attack vectors for Spectre

1. Kernel mitigation

^^^^^^^^^^^^^^^^^^^^

Spectre variant 1

~~~~~~~~~~~~~~~~~

   For the Spectre variant 1, vulnerable kernel code (as determined

   by code audit or scanning tools) is annotated on a case by case

   basis to use nospec accessor macros for bounds clipping :ref:`[2]

   <spec_ref2>` to avoid any usable disclosure gadgets. However, it may

   not cover all attack vectors for Spectre variant 1.

   Copy-from-user code has an LFENCE barrier to prevent the access_ok()

   check from being mis-speculated.  The barrier is done by the

   barrier_nospec() macro.

   For the swapgs variant of Spectre variant 1, LFENCE barriers are

   added to interrupt, exception and NMI entry where needed.  These

   barriers are done by the FENCE_SWAPGS_KERNEL_ENTRY and

   FENCE_SWAPGS_USER_ENTRY macros.

Spectre variant 2

~~~~~~~~~~~~~~~~~

   For Spectre variant 2 mitigation, the compiler turns indirect calls or

   jumps in the kernel into equivalent return trampolines (retpolines)

   :ref:`[3] <spec_ref3>` :ref:`[9] <spec_ref9>` to go to the target

Spectre variant 2 mitigation can be disabled or force enabled at the

kernel command line.

	nospectre_v1

		[X86,PPC] Disable mitigations for Spectre Variant 1

		(bounds check bypass). With this option data leaks are

		possible in the system.

	nospectre_v2

		[X86] Disable all mitigations for the Spectre variant 2

				expose users to several CPU vulnerabilities.

				Equivalent to: nopti [X86,PPC]

					       kpti=0 [ARM64]

					       nospectre_v1 [PPC]

					       nospectre_v1 [X86,PPC]

					       nobp=0 [S390]

					       nospectre_v2 [X86,PPC,S390,ARM64]

					       spectre_v2_user=off [X86]

			nosmt=force: Force disable SMT, cannot be undone

				     via the sysfs control file.

	nospectre_v1	[PPC] Disable mitigations for Spectre Variant 1 (bounds

			check bypass). With this option data leaks are possible

			in the system.

	nospectre_v1	[X86,PPC] Disable mitigations for Spectre Variant 1

			(bounds check bypass). With this option data leaks are

			possible in the system.

	nospectre_v2	[X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for

			the Spectre variant 2 (indirect branch prediction)

===================

RISC-V CPU Bindings

===================

The device tree allows to describe the layout of CPUs in a system through

the "cpus" node, which in turn contains a number of subnodes (ie "cpu")

defining properties for every cpu.

Bindings for CPU nodes follow the Devicetree Specification, available from:

https://www.devicetree.org/specifications/

with updates for 32-bit and 64-bit RISC-V systems provided in this document.

===========

Terminology

===========

This document uses some terminology common to the RISC-V community that is not

widely used, the definitions of which are listed here:

* hart: A hardware execution context, which contains all the state mandated by

  the RISC-V ISA: a PC and some registers.  This terminology is designed to

  disambiguate software's view of execution contexts from any particular

  microarchitectural implementation strategy.  For example, my Intel laptop is

  described as having one socket with two cores, each of which has two hyper

  threads.  Therefore this system has four harts.

=====================================

cpus and cpu node bindings definition

=====================================

The RISC-V architecture, in accordance with the Devicetree Specification,

requires the cpus and cpu nodes to be present and contain the properties

described below.

- cpus node

        Description: Container of cpu nodes

        The node name must be "cpus".

        A cpus node must define the following properties:

        - #address-cells

                Usage: required

                Value type: <u32>

                Definition: must be set to 1

        - #size-cells

                Usage: required

                Value type: <u32>

                Definition: must be set to 0

- cpu node

        Description: Describes a hart context

        PROPERTIES

        - device_type

                Usage: required

                Value type: <string>

                Definition: must be "cpu"

        - reg

                Usage: required

                Value type: <u32>

                Definition: The hart ID of this CPU node

        - compatible:

                Usage: required

                Value type: <stringlist>

                Definition: must contain "riscv", may contain one of

                            "sifive,rocket0"

        - mmu-type:

                Usage: optional

                Value type: <string>

                Definition: Specifies the CPU's MMU type.  Possible values are

                            "riscv,sv32"

                            "riscv,sv39"

                            "riscv,sv48"

        - riscv,isa:

                Usage: required

                Value type: <string>

                Definition: Contains the RISC-V ISA string of this hart.  These

                            ISA strings are defined by the RISC-V ISA manual.

Example: SiFive Freedom U540G Development Kit

---------------------------------------------

This system contains two harts: a hart marked as disabled that's used for

low-level system tasks and should be ignored by Linux, and a second hart that

Linux is allowed to run on.

        cpus {

                #address-cells = <1>;

                #size-cells = <0>;

                timebase-frequency = <1000000>;

                cpu@0 {

                        clock-frequency = <1600000000>;

                        compatible = "sifive,rocket0", "riscv";

                        device_type = "cpu";

                        i-cache-block-size = <64>;

                        i-cache-sets = <128>;

                        i-cache-size = <16384>;

                        next-level-cache = <&L15 &L0>;

                        reg = <0>;

                        riscv,isa = "rv64imac";

                        status = "disabled";

                        L10: interrupt-controller {

                                #interrupt-cells = <1>;

                                compatible = "riscv,cpu-intc";

                                interrupt-controller;

                        };

                };

                cpu@1 {

                        clock-frequency = <1600000000>;

                        compatible = "sifive,rocket0", "riscv";

                        d-cache-block-size = <64>;

                        d-cache-sets = <64>;

                        d-cache-size = <32768>;

                        d-tlb-sets = <1>;

                        d-tlb-size = <32>;

                        device_type = "cpu";

                        i-cache-block-size = <64>;

                        i-cache-sets = <64>;

                        i-cache-size = <32768>;

                        i-tlb-sets = <1>;

                        i-tlb-size = <32>;

                        mmu-type = "riscv,sv39";

                        next-level-cache = <&L15 &L0>;

                        reg = <1>;

                        riscv,isa = "rv64imafdc";

                        status = "okay";

                        tlb-split;

                        L13: interrupt-controller {

                                #interrupt-cells = <1>;

                                compatible = "riscv,cpu-intc";

                                interrupt-controller;

                        };

                };

        };

Example: Spike ISA Simulator with 1 Hart

----------------------------------------

This device tree matches the Spike ISA golden model as run with `spike -p1`.

        cpus {

                cpu@0 {

                        device_type = "cpu";

                        reg = <0x00000000>;

                        status = "okay";

                        compatible = "riscv";

                        riscv,isa = "rv64imafdc";

                        mmu-type = "riscv,sv48";

                        clock-frequency = <0x3b9aca00>;

                        interrupt-controller {

                                #interrupt-cells = <0x00000001>;

                                interrupt-controller;

                                compatible = "riscv,cpu-intc";

                        }

                }

        }

  - Paul Walmsley <paul.walmsley@sifive.com>

  - Palmer Dabbelt <palmer@sifive.com>

description: |

  This document uses some terminology common to the RISC-V community

  that is not widely used, the definitions of which are listed here:

  hart: A hardware execution context, which contains all the state

  mandated by the RISC-V ISA: a PC and some registers.  This

  terminology is designed to disambiguate software's view of execution

  contexts from any particular microarchitectural implementation

  strategy.  For example, an Intel laptop containing one socket with

  two cores, each of which has two hyperthreads, could be described as

  having four harts.

properties:

  compatible:

    items:

      User-Level ISA document, available from

      https://riscv.org/specifications/

      While the isa strings in ISA specification are case

      insensitive, letters in the riscv,isa string must be all

      lowercase to simplify parsing.

  timebase-frequency:

    type: integer

    minimum: 1

  compatible:

    items:

      - enum:

          - sifive,freedom-unleashed-a00

          - sifive,hifive-unleashed-a00

      - const: sifive,fu540-c000

      - const: sifive,fu540

...