diff options
Diffstat (limited to 'Documentation/userspace-api/spec_ctrl.rst')
| -rw-r--r-- | Documentation/userspace-api/spec_ctrl.rst | 45 |
1 files changed, 31 insertions, 14 deletions
diff --git a/Documentation/userspace-api/spec_ctrl.rst b/Documentation/userspace-api/spec_ctrl.rst index c4dbe6f7cdae..ca89151fc0a8 100644 --- a/Documentation/userspace-api/spec_ctrl.rst +++ b/Documentation/userspace-api/spec_ctrl.rst @@ -26,20 +26,23 @@ 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: - -==== ===================== =================================================== -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. -==== ===================== =================================================== +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. @@ -47,6 +50,8 @@ 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 ----------------------- @@ -92,6 +97,7 @@ Speculation misfeature controls * 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) @@ -101,3 +107,14 @@ Speculation misfeature controls * 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); |