^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) ===================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) Speculation Control
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) ===================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) Quite some CPUs have speculation-related misfeatures which are in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) fact vulnerabilities causing data leaks in various forms even across
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) privilege domains.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) The kernel provides mitigation for such vulnerabilities in various
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) forms. Some of these mitigations are compile-time configurable and some
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) can be supplied on the kernel command line.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) There is also a class of mitigations which are very expensive, but they can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) be restricted to a certain set of processes or tasks in controlled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) environments. The mechanism to control these mitigations is via
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) :manpage:`prctl(2)`.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) There are two prctl options which are related to this:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) * PR_GET_SPECULATION_CTRL
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) * PR_SET_SPECULATION_CTRL
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) PR_GET_SPECULATION_CTRL
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) -----------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) PR_GET_SPECULATION_CTRL returns the state of the speculation misfeature
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) which is selected with arg2 of prctl(2). The return value uses bits 0-3 with
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) the following meaning:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) ==== ====================== ==================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) Bit Define Description
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) ==== ====================== ==================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) 0 PR_SPEC_PRCTL Mitigation can be controlled per task by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) PR_SET_SPECULATION_CTRL.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) 1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) disabled.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) 2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) enabled.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) 3 PR_SPEC_FORCE_DISABLE Same as PR_SPEC_DISABLE, but cannot be undone. A
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) subsequent prctl(..., PR_SPEC_ENABLE) will fail.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) 4 PR_SPEC_DISABLE_NOEXEC Same as PR_SPEC_DISABLE, but the state will be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) cleared on :manpage:`execve(2)`.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) ==== ====================== ==================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) If all bits are 0 the CPU is not affected by the speculation misfeature.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) If PR_SPEC_PRCTL is set, then the per-task control of the mitigation is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) available. If not set, prctl(PR_SET_SPECULATION_CTRL) for the speculation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) misfeature will fail.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) .. _set_spec_ctrl:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) PR_SET_SPECULATION_CTRL
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) -----------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) PR_SET_SPECULATION_CTRL allows to control the speculation misfeature, which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) is selected by arg2 of :manpage:`prctl(2)` per task. arg3 is used to hand
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) in the control value, i.e. either PR_SPEC_ENABLE or PR_SPEC_DISABLE or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) PR_SPEC_FORCE_DISABLE.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) Common error codes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) ------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) ======= =================================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) Value Meaning
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) ======= =================================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) EINVAL The prctl is not implemented by the architecture or unused
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) prctl(2) arguments are not 0.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) ENODEV arg2 is selecting a not supported speculation misfeature.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) ======= =================================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) PR_SET_SPECULATION_CTRL error codes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) -----------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) ======= =================================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) Value Meaning
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) ======= =================================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) 0 Success
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) ERANGE arg3 is incorrect, i.e. it's neither PR_SPEC_ENABLE nor
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) PR_SPEC_DISABLE nor PR_SPEC_FORCE_DISABLE.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) ENXIO Control of the selected speculation misfeature is not possible.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) See PR_GET_SPECULATION_CTRL.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) EPERM Speculation was disabled with PR_SPEC_FORCE_DISABLE and caller
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) tried to enable it again.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) ======= =================================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) Speculation misfeature controls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) -------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) - PR_SPEC_STORE_BYPASS: Speculative Store Bypass
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) Invocations:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, 0, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_FORCE_DISABLE, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE_NOEXEC, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) - PR_SPEC_INDIR_BRANCH: Indirect Branch Speculation in User Processes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) (Mitigate Spectre V2 style attacks against user processes)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) Invocations:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) * prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, 0, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_ENABLE, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_DISABLE, 0, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) * prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIRECT_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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