projects / apple / xnu.git / blame
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| 5ba3f43e A |
1 | .\" Copyright (c) 2017, Apple Inc. All rights reserved. |
| 2 | .\" | |
| 3 | .Dd March 1, 2017 | |
| 4 | .Dt MONOTONIC 9 | |
| 5 | .Os Darwin | |
| 6 | .\" | |
| 7 | .Sh NAME | |
| 8 | .Nm monotonic | |
| 9 | .Nd performance counter access system | |
| 10 | .\" | |
| 11 | .Sh DESCRIPTION | |
| 12 | .Nm | |
| 13 | allows kernel and user space clients to configure and read hardware performance | |
| 14 | counters. The hardware counters can be virtualized to count per-thread and | |
| 15 | per-process. | |
| 16 | .Nm | |
| 17 | is split into three major layers: | |
| 18 | .Bl -dash | |
| 19 | .It | |
| 20 | The machine-dependent implementations manipulate hardware registers to configure | |
| 21 | and access the counters. This layer provides a machine-independent interface | |
| 22 | that can be used by the next layer. | |
| 23 | .It | |
| 24 | A set of hooks and kernel routines manage the counters and provide higher-level | |
| 25 | abstractions, like 64-bit counters and counting only events that occurred on a | |
| 26 | thread or in a process. | |
| 27 | .It | |
| 28 | A user space interface that is presented as device nodes under | |
| 29 | .Pa /dev/monotonic . | |
| 30 | See | |
| 31 | .Xr monotonic 4 . | |
| 32 | Mach thread and task ports are used for the per-thread and per-process counts, | |
| 33 | with special inspection routines. Some counter values are also reflected into | |
| 34 | .Fn getrusage , | |
| 35 | for use after a process has exited. See | |
| 36 | .Xr getrusage 2 . | |
| 37 | .El | |
| 38 | .Pp | |
| 39 | .\".Sh DIAGNOSTICS | |
| 40 | .\" | |
| 41 | .Sh SEE ALSO | |
| 42 | .Xr count 1 , | |
| 43 | .Xr mperf 1 , | |
| 44 | .Xr easyperf 1 , | |
| 45 | .Xr getrusage 2 , | |
| 46 | .Xr monotonic 4 , | |
| 47 | .Xr perf 1 | |
| 48 | .\" | |
| 49 | .Sh HISTORY | |
| 50 | .Nm | |
| 51 | replaces the kernel performance counter system, kpc. For the time being, | |
| 52 | .Nm | |
| 53 | backs portions of the existing kpc | |
| 54 | .Fn sysctl | |
| 55 | interface. Prior to kpc, the AppleProfileFamily kernel extensions provided | |
| 56 | performance counter interfaces. The kernel extensions themselves expanded upon | |
| 57 | functionality provided for PowerPC by CHUD. | |
| 58 | .\".Sh CAVEATS | |
| 59 | .\" | |
| 60 | .Sh SECURITY CONSIDERATIONS | |
| 61 | .Pp | |
| 62 | .Pp | |
| 63 | .Bl -dash | |
| 64 | .It | |
| 65 | Hardware performance counters are an ideal tool for side-channel attacks. By | |
| 66 | observing how the counters are affected by an otherwise opaque process, an | |
| 67 | attacker can obtain sensitive data or key material. | |
| 68 | .Pp | |
| 69 | For this reason, the hardware performance counters cannot be queried directly | |
| 70 | from user space. Instead, all processes, including those owned by root, can | |
| 71 | only query the thread and process counters if they have the corresponding Mach | |
| 72 | thread or task port. | |
| 73 | .It | |
| 74 | When used in sampling mode, hardware performance counters can induce interrupt | |
| 75 | storms that translate to denial-of-service attacks on a system. Even a careless | |
| 76 | user can stumble over this issue, since reasonable periods for some events are | |
| 77 | far too aggressive for others. | |
| 78 | .Pp | |
| 79 | If a hardware performance counter takes too many interrupts in a short amount of | |
| 80 | time, it will be disabled. | |
| 81 | .El |