mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git
synced 2026-05-02 18:17:50 -04:00
59af95e028
Starting with Panther Cove, the rdpmc user disable feature is supported. This feature allows the perf system to disable user space rdpmc reads at the counter level. Currently, when a global counter is active, any user with rdpmc rights can read it, even if perf access permissions forbid it (e.g., disallow reading ring 0 counters). The rdpmc user disable feature mitigates this security concern. Details: - A new RDPMC_USR_DISABLE bit (bit 37) in each EVNTSELx MSR indicates that the GP counter cannot be read by RDPMC in ring 3. - New RDPMC_USR_DISABLE bits in IA32_FIXED_CTR_CTRL MSR (bits 33, 37, 41, 45, etc.) for fixed counters 0, 1, 2, 3, etc. - When calling rdpmc instruction for counter x, the following pseudo code demonstrates how the counter value is obtained: If (!CPL0 && RDPMC_USR_DISABLE[x] == 1) ? 0 : counter_value; - RDPMC_USR_DISABLE is enumerated by CPUID.0x23.0.EBX[2]. This patch extends the current global user space rdpmc control logic via the sysfs interface (/sys/devices/cpu/rdpmc) as follows: - rdpmc = 0: Global user space rdpmc and counter-level user space rdpmc for all counters are both disabled. - rdpmc = 1: Global user space rdpmc is enabled during the mmap-enabled time window, and counter-level user space rdpmc is enabled only for non-system-wide events. This prevents counter data leaks as count data is cleared during context switches. - rdpmc = 2: Global user space rdpmc and counter-level user space rdpmc for all counters are enabled unconditionally. The new rdpmc settings only affect newly activated perf events; currently active perf events remain unaffected. This simplifies and cleans up the code. The default value of rdpmc remains unchanged at 1. For more details about rdpmc user disable, please refer to chapter 15 "RDPMC USER DISABLE" in ISE documentation. Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/20260114011750.350569-8-dapeng1.mi@linux.intel.com
This part of the documentation inside Documentation/ABI 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: (Optional) Kernel version this feature first showed up in. Note: git history often provides more accurate version info, so this field may be omitted. 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. Note: The fields should be use a simple notation, compatible with ReST markup. Also, the file **should not** have a top-level index, like:: === foo === 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.