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3b78ce4a34
Merge speculative store buffer bypass fixes from Thomas Gleixner: - rework of the SPEC_CTRL MSR management to accomodate the new fancy SSBD (Speculative Store Bypass Disable) bit handling. - the CPU bug and sysfs infrastructure for the exciting new Speculative Store Bypass 'feature'. - support for disabling SSB via LS_CFG MSR on AMD CPUs including Hyperthread synchronization on ZEN. - PRCTL support for dynamic runtime control of SSB - SECCOMP integration to automatically disable SSB for sandboxed processes with a filter flag for opt-out. - KVM integration to allow guests fiddling with SSBD including the new software MSR VIRT_SPEC_CTRL to handle the LS_CFG based oddities on AMD. - BPF protection against SSB .. this is just the core and x86 side, other architecture support will come separately. * 'speck-v20' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (49 commits) bpf: Prevent memory disambiguation attack x86/bugs: Rename SSBD_NO to SSB_NO KVM: SVM: Implement VIRT_SPEC_CTRL support for SSBD x86/speculation, KVM: Implement support for VIRT_SPEC_CTRL/LS_CFG x86/bugs: Rework spec_ctrl base and mask logic x86/bugs: Remove x86_spec_ctrl_set() x86/bugs: Expose x86_spec_ctrl_base directly x86/bugs: Unify x86_spec_ctrl_{set_guest,restore_host} x86/speculation: Rework speculative_store_bypass_update() x86/speculation: Add virtualized speculative store bypass disable support x86/bugs, KVM: Extend speculation control for VIRT_SPEC_CTRL x86/speculation: Handle HT correctly on AMD x86/cpufeatures: Add FEATURE_ZEN x86/cpufeatures: Disentangle SSBD enumeration x86/cpufeatures: Disentangle MSR_SPEC_CTRL enumeration from IBRS x86/speculation: Use synthetic bits for IBRS/IBPB/STIBP KVM: SVM: Move spec control call after restore of GS x86/cpu: Make alternative_msr_write work for 32-bit code x86/bugs: Fix the parameters alignment and missing void x86/bugs: Make cpu_show_common() static ... |
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This directory attempts to document the ABI between the Linux kernel and userspace, and the relative stability of these interfaces. Due to the everchanging nature of Linux, and the differing maturity levels, these interfaces should be used by userspace programs in different ways. We have four different levels of ABI stability, as shown by the four different subdirectories in this location. Interfaces may change levels of stability according to the rules described below. The different levels of stability are: stable/ This directory documents the interfaces that the developer has defined to be stable. Userspace programs are free to use these interfaces with no restrictions, and backward compatibility for them will be guaranteed for at least 2 years. Most interfaces (like syscalls) are expected to never change and always be available. testing/ This directory documents interfaces that are felt to be stable, as the main development of this interface has been completed. The interface can be changed to add new features, but the current interface will not break by doing this, unless grave errors or security problems are found in them. Userspace programs can start to rely on these interfaces, but they must be aware of changes that can occur before these interfaces move to be marked stable. Programs that use these interfaces are strongly encouraged to add their name to the description of these interfaces, so that the kernel developers can easily notify them if any changes occur (see the description of the layout of the files below for details on how to do this.) obsolete/ This directory documents interfaces that are still remaining in the kernel, but are marked to be removed at some later point in time. The description of the interface will document the reason why it is obsolete and when it can be expected to be removed. removed/ This directory contains a list of the old interfaces that have been removed from the kernel. Every file in these directories will contain the following information: What: Short description of the interface Date: Date created KernelVersion: Kernel version this feature first showed up in. Contact: Primary contact for this interface (may be a mailing list) Description: Long description of the interface and how to use it. Users: All users of this interface who wish to be notified when it changes. This is very important for interfaces in the "testing" stage, so that kernel developers can work with userspace developers to ensure that things do not break in ways that are unacceptable. It is also important to get feedback for these interfaces to make sure they are working in a proper way and do not need to be changed further. How things move between levels: Interfaces in stable may move to obsolete, as long as the proper notification is given. Interfaces may be removed from obsolete and the kernel as long as the documented amount of time has gone by. Interfaces in the testing state can move to the stable state when the developers feel they are finished. They cannot be removed from the kernel tree without going through the obsolete state first. It's up to the developer to place their interfaces in the category they wish for it to start out in. Notable bits of non-ABI, which should not under any circumstances be considered stable: - Kconfig. Userspace should not rely on the presence or absence of any particular Kconfig symbol, in /proc/config.gz, in the copy of .config commonly installed to /boot, or in any invocation of the kernel build process. - Kernel-internal symbols. Do not rely on the presence, absence, location, or type of any kernel symbol, either in System.map files or the kernel binary itself. See Documentation/process/stable-api-nonsense.rst.