From 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2023 18:24:12 -0800 Subject: Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ... --- .../admin-guide/hw-vuln/core-scheduling.rst | 226 +++++++++++++++++++++ 1 file changed, 226 insertions(+) create mode 100644 Documentation/admin-guide/hw-vuln/core-scheduling.rst (limited to 'Documentation/admin-guide/hw-vuln/core-scheduling.rst') diff --git a/Documentation/admin-guide/hw-vuln/core-scheduling.rst b/Documentation/admin-guide/hw-vuln/core-scheduling.rst new file mode 100644 index 000000000..cf1eeefdf --- /dev/null +++ b/Documentation/admin-guide/hw-vuln/core-scheduling.rst @@ -0,0 +1,226 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +Core Scheduling +=============== +Core scheduling support allows userspace to define groups of tasks that can +share a core. These groups can be specified either for security usecases (one +group of tasks don't trust another), or for performance usecases (some +workloads may benefit from running on the same core as they don't need the same +hardware resources of the shared core, or may prefer different cores if they +do share hardware resource needs). This document only describes the security +usecase. + +Security usecase +---------------- +A cross-HT attack involves the attacker and victim running on different Hyper +Threads of the same core. MDS and L1TF are examples of such attacks. The only +full mitigation of cross-HT attacks is to disable Hyper Threading (HT). Core +scheduling is a scheduler feature that can mitigate some (not all) cross-HT +attacks. It allows HT to be turned on safely by ensuring that only tasks in a +user-designated trusted group can share a core. This increase in core sharing +can also improve performance, however it is not guaranteed that performance +will always improve, though that is seen to be the case with a number of real +world workloads. In theory, core scheduling aims to perform at least as good as +when Hyper Threading is disabled. In practice, this is mostly the case though +not always: as synchronizing scheduling decisions across 2 or more CPUs in a +core involves additional overhead - especially when the system is lightly +loaded. When ``total_threads <= N_CPUS/2``, the extra overhead may cause core +scheduling to perform more poorly compared to SMT-disabled, where N_CPUS is the +total number of CPUs. Please measure the performance of your workloads always. + +Usage +----- +Core scheduling support is enabled via the ``CONFIG_SCHED_CORE`` config option. +Using this feature, userspace defines groups of tasks that can be co-scheduled +on the same core. The core scheduler uses this information to make sure that +tasks that are not in the same group never run simultaneously on a core, while +doing its best to satisfy the system's scheduling requirements. + +Core scheduling can be enabled via the ``PR_SCHED_CORE`` prctl interface. +This interface provides support for the creation of core scheduling groups, as +well as admission and removal of tasks from created groups:: + + #include + + int prctl(int option, unsigned long arg2, unsigned long arg3, + unsigned long arg4, unsigned long arg5); + +option: + ``PR_SCHED_CORE`` + +arg2: + Command for operation, must be one off: + + - ``PR_SCHED_CORE_GET`` -- get core_sched cookie of ``pid``. + - ``PR_SCHED_CORE_CREATE`` -- create a new unique cookie for ``pid``. + - ``PR_SCHED_CORE_SHARE_TO`` -- push core_sched cookie to ``pid``. + - ``PR_SCHED_CORE_SHARE_FROM`` -- pull core_sched cookie from ``pid``. + +arg3: + ``pid`` of the task for which the operation applies. + +arg4: + ``pid_type`` for which the operation applies. It is one of + ``PR_SCHED_CORE_SCOPE_``-prefixed macro constants. For example, if arg4 + is ``PR_SCHED_CORE_SCOPE_THREAD_GROUP``, then the operation of this command + will be performed for all tasks in the task group of ``pid``. + +arg5: + userspace pointer to an unsigned long for storing the cookie returned by + ``PR_SCHED_CORE_GET`` command. Should be 0 for all other commands. + +In order for a process to push a cookie to, or pull a cookie from a process, it +is required to have the ptrace access mode: `PTRACE_MODE_READ_REALCREDS` to the +process. + +Building hierarchies of tasks +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The simplest way to build hierarchies of threads/processes which share a +cookie and thus a core is to rely on the fact that the core-sched cookie is +inherited across forks/clones and execs, thus setting a cookie for the +'initial' script/executable/daemon will place every spawned child in the +same core-sched group. + +Cookie Transferral +~~~~~~~~~~~~~~~~~~ +Transferring a cookie between the current and other tasks is possible using +PR_SCHED_CORE_SHARE_FROM and PR_SCHED_CORE_SHARE_TO to inherit a cookie from a +specified task or a share a cookie with a task. In combination this allows a +simple helper program to pull a cookie from a task in an existing core +scheduling group and share it with already running tasks. + +Design/Implementation +--------------------- +Each task that is tagged is assigned a cookie internally in the kernel. As +mentioned in `Usage`_, tasks with the same cookie value are assumed to trust +each other and share a core. + +The basic idea is that, every schedule event tries to select tasks for all the +siblings of a core such that all the selected tasks running on a core are +trusted (same cookie) at any point in time. Kernel threads are assumed trusted. +The idle task is considered special, as it trusts everything and everything +trusts it. + +During a schedule() event on any sibling of a core, the highest priority task on +the sibling's core is picked and assigned to the sibling calling schedule(), if +the sibling has the task enqueued. For rest of the siblings in the core, +highest priority task with the same cookie is selected if there is one runnable +in their individual run queues. If a task with same cookie is not available, +the idle task is selected. Idle task is globally trusted. + +Once a task has been selected for all the siblings in the core, an IPI is sent to +siblings for whom a new task was selected. Siblings on receiving the IPI will +switch to the new task immediately. If an idle task is selected for a sibling, +then the sibling is considered to be in a `forced idle` state. I.e., it may +have tasks on its on runqueue to run, however it will still have to run idle. +More on this in the next section. + +Forced-idling of hyperthreads +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The scheduler tries its best to find tasks that trust each other such that all +tasks selected to be scheduled are of the highest priority in a core. However, +it is possible that some runqueues had tasks that were incompatible with the +highest priority ones in the core. Favoring security over fairness, one or more +siblings could be forced to select a lower priority task if the highest +priority task is not trusted with respect to the core wide highest priority +task. If a sibling does not have a trusted task to run, it will be forced idle +by the scheduler (idle thread is scheduled to run). + +When the highest priority task is selected to run, a reschedule-IPI is sent to +the sibling to force it into idle. This results in 4 cases which need to be +considered depending on whether a VM or a regular usermode process was running +on either HT:: + + HT1 (attack) HT2 (victim) + A idle -> user space user space -> idle + B idle -> user space guest -> idle + C idle -> guest user space -> idle + D idle -> guest guest -> idle + +Note that for better performance, we do not wait for the destination CPU +(victim) to enter idle mode. This is because the sending of the IPI would bring +the destination CPU immediately into kernel mode from user space, or VMEXIT +in the case of guests. At best, this would only leak some scheduler metadata +which may not be worth protecting. It is also possible that the IPI is received +too late on some architectures, but this has not been observed in the case of +x86. + +Trust model +~~~~~~~~~~~ +Core scheduling maintains trust relationships amongst groups of tasks by +assigning them a tag that is the same cookie value. +When a system with core scheduling boots, all tasks are considered to trust +each other. This is because the core scheduler does not have information about +trust relationships until userspace uses the above mentioned interfaces, to +communicate them. In other words, all tasks have a default cookie value of 0. +and are considered system-wide trusted. The forced-idling of siblings running +cookie-0 tasks is also avoided. + +Once userspace uses the above mentioned interfaces to group sets of tasks, tasks +within such groups are considered to trust each other, but do not trust those +outside. Tasks outside the group also don't trust tasks within. + +Limitations of core-scheduling +------------------------------ +Core scheduling tries to guarantee that only trusted tasks run concurrently on a +core. But there could be small window of time during which untrusted tasks run +concurrently or kernel could be running concurrently with a task not trusted by +kernel. + +IPI processing delays +~~~~~~~~~~~~~~~~~~~~~ +Core scheduling selects only trusted tasks to run together. IPI is used to notify +the siblings to switch to the new task. But there could be hardware delays in +receiving of the IPI on some arch (on x86, this has not been observed). This may +cause an attacker task to start running on a CPU before its siblings receive the +IPI. Even though cache is flushed on entry to user mode, victim tasks on siblings +may populate data in the cache and micro architectural buffers after the attacker +starts to run and this is a possibility for data leak. + +Open cross-HT issues that core scheduling does not solve +-------------------------------------------------------- +1. For MDS +~~~~~~~~~~ +Core scheduling cannot protect against MDS attacks between the siblings +running in user mode and the others running in kernel mode. Even though all +siblings run tasks which trust each other, when the kernel is executing +code on behalf of a task, it cannot trust the code running in the +sibling. Such attacks are possible for any combination of sibling CPU modes +(host or guest mode). + +2. For L1TF +~~~~~~~~~~~ +Core scheduling cannot protect against an L1TF guest attacker exploiting a +guest or host victim. This is because the guest attacker can craft invalid +PTEs which are not inverted due to a vulnerable guest kernel. The only +solution is to disable EPT (Extended Page Tables). + +For both MDS and L1TF, if the guest vCPU is configured to not trust each +other (by tagging separately), then the guest to guest attacks would go away. +Or it could be a system admin policy which considers guest to guest attacks as +a guest problem. + +Another approach to resolve these would be to make every untrusted task on the +system to not trust every other untrusted task. While this could reduce +parallelism of the untrusted tasks, it would still solve the above issues while +allowing system processes (trusted tasks) to share a core. + +3. Protecting the kernel (IRQ, syscall, VMEXIT) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Unfortunately, core scheduling does not protect kernel contexts running on +sibling hyperthreads from one another. Prototypes of mitigations have been posted +to LKML to solve this, but it is debatable whether such windows are practically +exploitable, and whether the performance overhead of the prototypes are worth +it (not to mention, the added code complexity). + +Other Use cases +--------------- +The main use case for Core scheduling is mitigating the cross-HT vulnerabilities +with SMT enabled. There are other use cases where this feature could be used: + +- Isolating tasks that needs a whole core: Examples include realtime tasks, tasks + that uses SIMD instructions etc. +- Gang scheduling: Requirements for a group of tasks that needs to be scheduled + together could also be realized using core scheduling. One example is vCPUs of + a VM. -- cgit v1.2.3