From 55fc280e951ab2b39f3dcb640edc1b1eebc6d173 Mon Sep 17 00:00:00 2001 From: "Rob Herring (Arm)" Date: Mon, 31 Aug 2026 14:43:51 -0500 Subject: Input: tsc2007 - read "ti,poll-period" as u32 The "ti,poll-period" property is documented as a normal uint32 cell. The driver used a u64 helper, which makes the helper type disagree with the schema even though the stored value is still small. Read "ti,poll-period" with the u32 helper matching the documented DT cell size. Assisted-by: Codex:gpt-5-5 Signed-off-by: Rob Herring (Arm) Link: https://patch.msgid.link/20260831194352.1185860-1-robh@kernel.org Signed-off-by: Dmitry Torokhov --- Documentation/userspace-api/spec_ctrl.rst | 124 ++++++++++++++++++++++++++++++ 1 file changed, 124 insertions(+) create mode 100644 Documentation/userspace-api/spec_ctrl.rst (limited to 'Documentation/userspace-api/spec_ctrl.rst') diff --git a/Documentation/userspace-api/spec_ctrl.rst b/Documentation/userspace-api/spec_ctrl.rst new file mode 100644 index 000000000..61fe020b2 --- /dev/null +++ b/Documentation/userspace-api/spec_ctrl.rst @@ -0,0 +1,124 @@ +=================== +Speculation Control +=================== + +Quite some CPUs have speculation-related misfeatures which are in +fact vulnerabilities causing data leaks in various forms even across +privilege domains. + +The kernel provides mitigation for such vulnerabilities in various +forms. Some of these mitigations are compile-time configurable and some +can be supplied on the kernel command line. + +There is also a class of mitigations which are very expensive, but they can +be restricted to a certain set of processes or tasks in controlled +environments. The mechanism to control these mitigations is via +:manpage:`prctl(2)`. + +There are two prctl options which are related to this: + + * PR_GET_SPECULATION_CTRL + + * PR_SET_SPECULATION_CTRL + +PR_GET_SPECULATION_CTRL +----------------------- + +PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature +which is selected with arg2 of prctl(2). The return value uses bits 0-3 with +the following meaning (with the caveat that PR_SPEC_L1D_FLUSH has less obvious +semantics, see documentation for that specific control below): + +==== ====================== ================================================== +Bit Define Description +==== ====================== ================================================== +0 PR_SPEC_PRCTL Mitigation can be controlled per task by + PR_SET_SPECULATION_CTRL. +1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is + disabled. +2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is + enabled. +3 PR_SPEC_FORCE_DISABLE Same as PR_SPEC_DISABLE, but cannot be undone. A + subsequent prctl(..., PR_SPEC_ENABLE) will fail. +4 PR_SPEC_DISABLE_NOEXEC Same as PR_SPEC_DISABLE, but the state will be + cleared on :manpage:`execve(2)`. +==== ====================== ================================================== + +If all bits are 0 the CPU is not affected by the speculation misfeature. + +If PR_SPEC_PRCTL is set, then the per-task control of the mitigation is +available. If not set, prctl(PR_SET_SPECULATION_CTRL) for the speculation +misfeature will fail. + +.. _set_spec_ctrl: + +PR_SET_SPECULATION_CTRL +----------------------- + +PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which +is selected by arg2 of :manpage:`prctl(2)` per task. arg3 is used to hand +in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE or +PR_SPEC_FORCE_DISABLE. + +Common error codes +------------------ +======= ================================================================= +Value Meaning +======= ================================================================= +EINVAL The prctl is not implemented by the architecture or unused + prctl(2) arguments are not 0. + +ENODEV arg2 is selecting a not supported speculation misfeature. +======= ================================================================= + +PR_SET_SPECULATION_CTRL error codes +----------------------------------- +======= ================================================================= +Value Meaning +======= ================================================================= +0 Success + +ERANGE arg3 is incorrect, i.e. it's neither PR_SPEC_ENABLE nor + PR_SPEC_DISABLE nor PR_SPEC_FORCE_DISABLE. + +ENXIO For PR_SPEC_STORE_BYPASS: control of the selected speculation misfeature + is not possible via prctl, because of the system's boot configuration. + +EPERM Speculation was disabled with PR_SPEC_FORCE_DISABLE and caller tried to + enable it again. + +EPERM For PR_SPEC_L1D_FLUSH and PR_SPEC_INDIRECT_BRANCH: control of the + mitigation is not possible because of the system's boot configuration. + +======= ================================================================= + +Speculation misfeature controls +------------------------------- +- PR_SPEC_STORE_BYPASS: Speculative Store Bypass + + Invocations: + * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, 0, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE_NOEXEC, 0, 0); + +- PR_SPEC_INDIR_BRANCH: Indirect Branch Speculation in User Processes + (Mitigate Spectre V2 style attacks against user processes) + + Invocations: + * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, 0, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_ENABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_DISABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0); + +- PR_SPEC_L1D_FLUSH: Flush L1D Cache on context switch out of the task + (works only when tasks run on non SMT cores) + +For this control, PR_SPEC_ENABLE means that the **mitigation** is enabled (L1D +is flushed), PR_SPEC_DISABLE means it is disabled. + + Invocations: + * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_L1D_FLUSH, 0, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_L1D_FLUSH, PR_SPEC_ENABLE, 0, 0); + * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_L1D_FLUSH, PR_SPEC_DISABLE, 0, 0); -- cgit v1.3.1